EP2977477B1 - Process for converting an alloy and process for producing a landing gear part - Google Patents

Process for converting an alloy and process for producing a landing gear part Download PDF

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EP2977477B1
EP2977477B1 EP15177409.8A EP15177409A EP2977477B1 EP 2977477 B1 EP2977477 B1 EP 2977477B1 EP 15177409 A EP15177409 A EP 15177409A EP 2977477 B1 EP2977477 B1 EP 2977477B1
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alloy
type
temperature
length
deformation
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German (de)
French (fr)
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EP2977477A1 (en
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Francis Soniak
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Safran Landing Systems SAS
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Safran Landing Systems SAS
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium

Definitions

  • the invention relates to a process for converting an alloy containing predominantly titanium.
  • Titanium alloys contain, as a percentage by weight of the alloy, a majority of titanium and in particular at least 60% of the mass of the alloy is formed of titanium.
  • Inspection of titanium alloy parts can be done using ultrasonic measurements.
  • patent document EP1136582A1 discloses a titanium alloy conversion process for modifying the characteristics of the titanium alloy to facilitate ultrasonic analysis.
  • the object of the invention is to obtain a process for converting an alloy comprising, in mass percentage of the alloy, predominantly titanium, this process intended to promote the improvement of the quality of parts produced using of the alloy converted according to the process of the invention.
  • the invention also relates to obtaining a method for producing an aircraft landing gear part.
  • the transus ⁇ temperature, T ⁇ is the temperature above which a transition is observed from at least some of the structures of the alloy which are in the ⁇ phase to structures of the alloy. in ⁇ phase.
  • the ⁇ -phase alloy portion has a compact hexagonal micro crystallographic structure.
  • the ⁇ -phase alloy portion has a centered cubic crystallographic microstructure.
  • the parts of a batch of parts produced from the titanium alloy converted according to the process of the invention have homogenized characteristics from the point of view of the micro structure, from the point of view of the distribution of grain sizes in ⁇ phases contained in the alloy and from the point of view of chemical composition (the chemical species are better distributed in the alloy converted according to the process of the invention than they were in the ingot before implementation of the different stages of the process of the invention).
  • the overall quality of the batch of parts is improved because the alloy constituting these parts has homogeneous characteristics between the parts of the batch.
  • the ingot which weighs several tons, typically an ingot weighs 3 to 7 tons and measures more than 2 meters in height, there is a stratification of the ingot such that the lower and central part of the ingot presents elongated crystals of length and average section much greater than the length and average section of the crystals located in the upper part of the ingot.
  • the first step of the first type A is carried out at a first temperature T1 higher than the transus temperature ⁇ which allows a transformation of at least part of the crystallographic alloy structures which are in phase ⁇ towards crystallographic structures in ⁇ phase.
  • the mechanical deformation / plastic deformation of the large grains of the alloy in the ⁇ phase leads to a breakage of these large grains in the ⁇ phase which are then recrystallized into small grains still in the ⁇ phase.
  • the first step of the second type A' which is carried out below the transus temperature ⁇ , in this case at a temperature T4, to preserve the nature of the ⁇ and ⁇ phases present in the material while applying to this same alloy, a plastic mechanical deformation which has the effect of creating/accumulating internal mechanical stresses in the alloy and around the grains in the ⁇ phase.
  • the temperature of the alloy is then raised above the transus temperature ⁇ until reaching a second temperature T2 which is strictly lower than the first temperature T1.
  • the mechanical stresses accumulated around the ⁇ phase grains during the first step of the second type A' again generate ruptures/dislocations of the ⁇ grains which have the largest sizes and which are subjected to the largest constraints. The effect of these dislocations is to promote the recrystallization of the largest ⁇ alloy grains.
  • This second step of the first type B is a recrystallization step, which makes it possible to prepare a first homogenization of the size of the ⁇ grains, by accumulation of dislocations in the largest grains, or the least well oriented with respect to the bulk of the microstructure.
  • the temperature of the alloy is lowered again so that it has a current temperature T4 lower than the transus temperature ⁇ , T ⁇ , and a plastic deformation is again applied to the alloy to once again create new mechanical stresses in the alloy and around the grains in the ⁇ phase.
  • step B' is carried out below the transus ⁇ temperature, the ⁇ and ⁇ phases of the grains present in the alloy are preserved and only mechanical stresses are generated around the most heterogeneous ⁇ grains with respect to the microstructure.
  • the temperature of the alloy is increased again so that it has a current temperature, called the third temperature T3, which is higher than the temperature of transus ⁇ , but strictly lower than the second temperature T2 which had been reached during the second stage of the first type B.
  • the mechanical stresses accumulated, around the ⁇ grains, during the second stage of the second type B' again generate ruptures/dislocations of the ⁇ grains which have the largest sizes and which are subject to the greatest stresses. The effect of these new dislocations is always to promote the recrystallization of the ⁇ grains which contain the most dislocations.
  • the alloy is thus homogenized again.
  • first, second and third stages of the first type are carried out by gradually lowering the temperature while remaining above the transus temperature ⁇ makes it possible to gradually create increasingly finer dislocations to promote the precipitation of the grains d the most heterogeneous ⁇ -phase alloy. All these steps of the conversion process according to the invention make it possible to homogenize the crystallographic structure of the alloy both in terms of the distribution of the ⁇ phase grains and the ⁇ phase grains in the alloy and in terms of the dimensions of the alloy. these respective grains.
  • the alloy thus converted has more homogeneous mechanical characteristics which makes it possible to homogenize the characteristics according to the envisaged directions of the metal parts obtained at from this alloy.
  • each plastic deformation implemented during a step of the second type A', B', C' is such that it tends to at least partially reverse the effect of deformation applied to the alloy during the step of the first type immediately preceding this step of the second type.
  • reversal of deformation effect is meant a reversal of at least one of the deformations undergone by the alloy.
  • each of the plastic deformations implemented during the stages of the first type are deformations by compression of the alloy following a direction of alloy compression common to all the stages of the first type, these plastic deformations implemented during the steps of the first type each have an effect of reducing the length Lx of the alloy.
  • the length Lx of the alloy is the largest dimension of the alloy or block of alloy subjected to deformation. Whether the alloy is in the form of an ingot or billet, this alloy length Lx always remains the largest measurable dimension on this alloy and this length Lx is therefore a common length of the alloy measured before subjecting the alloy to a new stage of deformation.
  • each of the plastic deformations implemented during the steps of the second type A', B', C' are deformations by compression of the alloy oriented so as to obtain at each step of the second type an increase in the length (Lx) of the alloy.
  • the plastic deformations implemented during operations of the second type are obtained by compressing the alloy in compression directions perpendicular to the alloy compression direction common to all stages of the first type.
  • figure 1 which illustrates the process according to the invention.
  • the purpose of the process according to the invention is to enable the conversion of a titanium alloy initially in the form of an ingot, this conversion process making it possible to homogenize the micro-structural characteristics of the alloy.
  • the invention essentially relates to the conversion process according to the invention, it also relates to a process for producing a part such as a rod, a bogie or an aircraft landing box, or any part of a size comparable to a undercarriage rod (length greater than 1 meter), made from an alloy converted in accordance with the alloy conversion process according to the invention.
  • This production process comprises, in addition to the alloy conversion process according to the invention, the aforementioned subsequent stages of forging, machining and aging to obtain a large, almost finished undercarriage part, such as a rod, a bogie, a landing box.
  • the first step of the conversion process according to the invention consists of producing an alloy comprising, as a mass percentage of the alloy, predominantly titanium.
  • This alloy is chosen to have a ⁇ T ⁇ transus temperature of between 800°C and 950°C and preferably 900°C.
  • this fifth alloy contains, in mass proportion, at least 84% Titanium and at least the following elements: - Aluminum 4.0 - 7.5% - Vanadium 3.5 - 5.5% - Molybdenum 4.5-7.5% - Chromium 1.8-3.6% - Iron 0.2-0.5% - Hafnium 0.1-1.1% - Oxygen 0.1-0.3% - Carbon 0.01-0.2%.
  • Each of these titanium alloys has its own transus temperature ⁇ T ⁇ .
  • the ⁇ transus temperature is the temperature from which a transition from ⁇ -phase alloy structures to ⁇ -phase alloy structures is observed.
  • the alloy thus produced is cast to manufacture an ingot 1 composed of said alloy.
  • the process comprises a third step of the second type C'.
  • T1 defined by (T ⁇ + 200°C) ⁇ T1 ⁇ (T ⁇ +300°C); T2 defined by T2 ⁇ T1 and (T ⁇ + 100°C) ⁇ T2 ⁇ (T ⁇ + 200°C); T3 defined by T3 ⁇ T2 ⁇ T1 and (T ⁇ + 50°C) ⁇ T3 ⁇ (T ⁇ + 150°C); T4 which is the fourth temperature used at each of the stages of the second type is defined by (T ⁇ -65°C) ⁇ T4 ⁇ (T ⁇ -35°C) or preferably by (T ⁇ -55°C) ⁇ T4 ⁇ ( T ⁇ -45°C).
  • each of the steps of the second type is implemented at the fourth temperature T4 between the transus temperature ⁇ (T ⁇ ) minus 50°C to plus or minus 15°C and preferably to plus or minus 5° C close.
  • T ⁇ 800°C
  • T1 1100°C
  • T2 1000°C
  • T3 900°C
  • T4 750°C.
  • These temperatures T1, T2, T3, T4 are checked if they are between +/-15°C of the indicated temperature and preferably between +/-5°C of this temperature.
  • the choice of the fourth temperature T4 makes it possible to keep the ⁇ and ⁇ phases present in the alloy without accumulating too much stress around the ⁇ grains.
  • the ingot 1 formed from the alloy has a current length Lx defining a main axis X-X of the alloy.
  • the direction of alloy compression is oriented parallel to this main alloy axis, and more particularly parallel to this length of the ingot.
  • the directions of compression of the alloy which are implemented during the steps of the second type A', B', C' are perpendicular to the length of the ingot, that is to say perpendicular to the main axis X-X.
  • the compressions implemented during the steps of the first type A, B, C are carried out by placing the ingot between elements of a press approaching each other in a direction parallel to the length of the ingot.
  • the compressions implemented during the steps of the second type A', B', C' are obtained by crushing the alloy between shaped or non-shaped tools placed opposite each other to cause a reduction in section of the alloy and thus a progressive elongation of the alloy.
  • the deformation carried out during the first step of the first type A comprises at least one upsetting operation R reducing the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured before implementation of this first step of the first type A.
  • the deformation carried out during the second step of the first type B also includes an upsetting operation R reducing the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured after implementation of the first step of the second type A' and before implementation work of the second stage of the first type B.
  • the deformation carried out during the third stage of the first type C also includes an upsetting R reducing the length Lx of the alloy by 15 to 20% of the length Lx of the alloy measured after implementation of the second stage of the second type B' and before implementation of the third step of the first type C.
  • the upsetting R is an operation of compression of the alloy along its length Lx, that is to say along the axis X-X of the alloy.
  • the deformation E1 carried out during the first step of the second type A' is carried out to increase the length Lx of the alloy from 20 to 30% of the length Lx of the alloy measured after implementation of the first step of the first type A and before this increase in length Lx implementation of the first step of the second type A'.
  • the deformation E4 carried out during the second step of the second type B' is adapted to increase the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured after implementation of the second step of the first type B and before the increase in length Lx carried out during this second step of the second type B'.
  • this third step C' makes it possible to give the alloy a shape and dimensions suitable for its subsequent forging to obtain 'a forged part.
  • This third step of the second type C' can be adapted to increase the length Lx of the alloy by at least 30% of the length Lx of the alloy Lx measured after implementation of the third step of the first type C and before implementation of this increase in length Lx carried out in the third step of the second type C'.
  • a cutting step X is carried out along a transverse plane of the alloy so as to obtain two elongated bar-shaped parts called billets 1', 1''.
  • these parts/billets 1', 1" are of identical shapes to each other.
  • the shape of a billet intended to form a large part of an aircraft undercarriage is substantially straight cylindrical with a length of between 2 m and 3 m and with a diameter of between 0.4 and 0.5 m.
  • the alloy ingot before implementation of the first stage of the first type A, is of right cylindrical shape with a length of between 3m and 5m and a diameter of between 0.6m and 1.2m.
  • the volume of two billets 1', 1" is less than the volume of the ingot, which implies that part of the alloy was evacuated during the different stages of the alloy conversion process according to the invention.
  • the billet 1' resulting from the process is formed of a converted alloy whose microstructure is homogenized at least in terms of grain dimensions in ⁇ phase and distribution of these grains in the alloy compared to the microstructure observed before implementation of step A of the process.

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Description

L'invention concerne un procédé de conversion d'alliage contenant majoritairement du titane.The invention relates to a process for converting an alloy containing predominantly titanium.

ARRIERE PLAN DE L'INVENTIONBACKGROUND OF THE INVENTION

Plus particulièrement, l'invention concerne un procédé de conversion d'un alliage comportant, en pourcentage massique de l'alliage, majoritairement du titane, cet alliage présentant une température de transus β à partir de laquelle on observe une transition de structures de l'alliage en phase α vers des structures de l'alliage en phase β, le procédé comportant :

  • une étape de fabrication d'un lingot (1) composé dudit alliage ;
  • au moins des première, seconde et troisième étapes d'un premier type consistant à déformer plastiquement l'alliage issu dudit lingot alors qu'il est à une température courante strictement supérieure à la température de transus β; et
  • au moins des première et seconde étapes d'un second type consistant à déformer plastiquement l'alliage issu dudit lingot alors qu'il est à une température courante strictement inférieure à la température de transus β.
More particularly, the invention relates to a process for converting an alloy comprising, in mass percentage of the alloy, predominantly titanium, this alloy having a transus temperature β from which a transition of structures of the α-phase alloy towards structures of the β-phase alloy, the process comprising:
  • a step of manufacturing an ingot (1) composed of said alloy;
  • at least first, second and third steps of a first type consisting of plastically deforming the alloy from said ingot while it is at a current temperature strictly higher than the transus β temperature; And
  • at least first and second steps of a second type consisting of plastically deforming the alloy resulting from said ingot while it is at a current temperature strictly lower than the transus β temperature.

Les alliages titane contiennent, en pourcentage massique de l'alliage, majoritairement du titane et en particulier au moins 60% de la masse de l'alliage est formée de titane.Titanium alloys contain, as a percentage by weight of the alloy, a majority of titanium and in particular at least 60% of the mass of the alloy is formed of titanium.

Malgré les procédés de conversion d'alliage connus, comme le procédé de conversion du document brevet EP2623628A1 , on a constaté une hétérogénéité de résistance mécanique entre des pièces appartenant à un même lot de pièces obtenues à partir d'un même alliage.Despite known alloy conversion processes, such as the patent document conversion process EP2623628A1 , heterogeneity in mechanical resistance was noted between parts belonging to the same batch of parts obtained from the same alloy.

Pour des questions de qualité de production, il est souhaitable que des pièces similaires obtenues à partir d'un même alliage titane présentent une homogénéité de résistance mécanique.For reasons of production quality, it is desirable that similar parts obtained from the same titanium alloy have uniform mechanical strength.

L'inspection de pièces en alliage titane peut se faire à l'aide de mesures par ultrasons.Inspection of titanium alloy parts can be done using ultrasonic measurements.

Ainsi, le document brevet EP1136582A1 divulgue un procédé de conversion d'alliage titane permettant de modifier les caractéristiques de l'alliage titane pour faciliter l'analyse par ultrasons.Thus, the patent document EP1136582A1 discloses a titanium alloy conversion process for modifying the characteristics of the titanium alloy to facilitate ultrasonic analysis.

OBJET DE L'INVENTIONOBJECT OF THE INVENTION

L'invention a pour objet l'obtention d'un procédé de conversion d'un alliage comportant, en pourcentage massique de l'alliage, majoritairement du titane, ce procédé devant favoriser l'amélioration de la qualité de pièces produites à l'aide de l'alliage converti suivant le procédé de l'invention.The object of the invention is to obtain a process for converting an alloy comprising, in mass percentage of the alloy, predominantly titanium, this process intended to promote the improvement of the quality of parts produced using of the alloy converted according to the process of the invention.

L'invention a également pour objet l'obtention d'un procédé de production d'une pièce d'atterrisseur d'aéronef.The invention also relates to obtaining a method for producing an aircraft landing gear part.

RESUME DE L'INVENTIONSUMMARY OF THE INVENTION

En vue de réaliser cet objet, il est proposé selon l'invention, un procédé de conversion d'un alliage conforme à l'objet de la revendication 1. Un procédé de production d'une pièce d'atterrisseur d'aéronef selon l'invention est défini dans la revendication 12. Les modes préférés sont définis dans les revendications 2-11.In order to achieve this object, it is proposed according to the invention, a method of converting an alloy conforming to the object of claim 1. A method of producing an aircraft undercarriage part according to invention is defined in claim 12. Preferred modes are defined in claims 2-11.

Pour la compréhension de l'invention, la température de transus β, Tβ, est la température au-dessus de laquelle on observe une transition de certaines au moins des structures de l'alliage qui sont en phase α vers des structures de l'alliage en phase β.To understand the invention, the transus β temperature, Tβ, is the temperature above which a transition is observed from at least some of the structures of the alloy which are in the α phase to structures of the alloy. in β phase.

La portion d'alliage en phase α présente une micro structure cristallographique hexagonale compacte.The α-phase alloy portion has a compact hexagonal micro crystallographic structure.

La portion d'alliage en phase β présente une micro structure cristallographique cubique centrée.The β-phase alloy portion has a centered cubic crystallographic microstructure.

Ainsi, lorsque l'on passe au-dessus de cette température de transus β, on constate que des portions de l'alliage qui se présentaient sous forme hexagonale compacte, se transforment en portions d'alliage cubique centrée. L'enchaînement d'étapes selon le procédé de l'invention combine traitements thermiques et déformations mécaniques plastiques de l'alliage accomplies de manière à homogénéiser la micro structure interne de l'alliage en homogénéisant progressivement la taille des cristaux / grains qui composent l'alliage.Thus, when we pass above this transus β temperature, we see that portions of the alloy which were in compact hexagonal form are transformed into portions of centered cubic alloy. The sequence of steps according to the process of the invention combines heat treatments and deformations plastic mechanics of the alloy accomplished in such a way as to homogenize the internal micro structure of the alloy by progressively homogenizing the size of the crystals/grains that make up the alloy.

Ainsi, les pièces d'un lot de pièces produit à partir de l'alliage titane converti suivant le procédé de l'invention présentent des caractéristiques homogénéisées du point de vu de la micro structure, du point de vue de la répartition des tailles des grains en phases β contenus dans l'alliage et du point de vu de composition chimique (les espèces chimiques sont mieux réparties dans l'alliage converti suivant le procédé de l'invention qu'elles ne l'étaient dans le lingot avant mise en oeuvre des différentes étapes du procédé de l'invention).Thus, the parts of a batch of parts produced from the titanium alloy converted according to the process of the invention have homogenized characteristics from the point of view of the micro structure, from the point of view of the distribution of grain sizes in β phases contained in the alloy and from the point of view of chemical composition (the chemical species are better distributed in the alloy converted according to the process of the invention than they were in the ingot before implementation of the different stages of the process of the invention).

Ainsi, la qualité globale du lot de pièces est améliorée car l'alliage constituant ces pièces présente des caractéristiques homogènes entre les pièces du lot.Thus, the overall quality of the batch of parts is improved because the alloy constituting these parts has homogeneous characteristics between the parts of the batch.

Lors de la formation du lingot, qui pèse plusieurs tonnes, typiquement un lingot pèse de 3 à 7 tonnes et mesure plus de 2 mètres de hauteur, on constate une stratification du lingot telle que la partie inférieure et centrale du lingot présente des cristaux allongés de longueur et section moyenne largement supérieure à la longueur et à la section moyenne des cristaux se trouvant en partie supérieure du lingot.During the formation of the ingot, which weighs several tons, typically an ingot weighs 3 to 7 tons and measures more than 2 meters in height, there is a stratification of the ingot such that the lower and central part of the ingot presents elongated crystals of length and average section much greater than the length and average section of the crystals located in the upper part of the ingot.

La première étape du premier type A est réalisée à une première température T1 supérieure à la température de transus β ce qui permet d'avoir une transformation d'une partie au moins des structures cristallographiques d'alliage qui sont en phase α vers des structures cristallographiques en phase β. La déformation mécanique / déformation plastique des gros grains de l'alliage en phase β entraine une cassure de ces gros grains en phase β qui sont alors recristallisés en petits grains toujours en phase β. On a ici un début d'homogénéisation de l'alliage du lingot en termes de nature de phases α et β présentes dans l'alliage et de taille de grains β.The first step of the first type A is carried out at a first temperature T1 higher than the transus temperature β which allows a transformation of at least part of the crystallographic alloy structures which are in phase α towards crystallographic structures in β phase. The mechanical deformation / plastic deformation of the large grains of the alloy in the β phase leads to a breakage of these large grains in the β phase which are then recrystallized into small grains still in the β phase. Here we have the beginning of homogenization of the alloy of the ingot in terms of the nature of the α and β phases present in the alloy and the size of the β grains.

La première étape du second type A' qui est réalisée en dessous de la température de transus β, en l'occurrence à une température T4, pour conserver la nature des phases α et β présentes dans le matériau tout en appliquant à ce même alliage, une déformation mécanique plastique qui a pour effet de créer / accumuler des contraintes mécaniques internes dans l'alliage et autour des grains en phase β.The first step of the second type A' which is carried out below the transus temperature β, in this case at a temperature T4, to preserve the nature of the α and β phases present in the material while applying to this same alloy, a plastic mechanical deformation which has the effect of creating/accumulating internal mechanical stresses in the alloy and around the grains in the β phase.

Lors de l'étape d'après qui est la seconde étape du premier type B, on remonte alors la température de l'alliage au-dessus de la température de transus β jusqu'à atteindre une seconde température T2 qui est strictement inférieure à la première température T1. Lors de cette étape B, les contraintes mécaniques accumulées autour des grains en phase β lors de la première étape du second type A', génèrent à nouveau des ruptures / dislocations des grains β qui ont les plus grandes tailles et qui sont soumis aux plus grandes contraintes. L'effet de ces dislocations est de favoriser la recristallisation des grains d'alliage β les plus gros. Cette seconde étape du premier type B est une étape de recristallisation, qui permet de préparer une première homogénéisation la taille des grains β, par accumulation de dislocations dans les grains les plus gros, ou les moins bien orientés par rapport à l'essentiel de la microstructure.During the next step which is the second step of the first type B, the temperature of the alloy is then raised above the transus temperature β until reaching a second temperature T2 which is strictly lower than the first temperature T1. During this step B, the mechanical stresses accumulated around the β phase grains during the first step of the second type A', again generate ruptures/dislocations of the β grains which have the largest sizes and which are subjected to the largest constraints. The effect of these dislocations is to promote the recrystallization of the largest β alloy grains. This second step of the first type B is a recrystallization step, which makes it possible to prepare a first homogenization of the size of the β grains, by accumulation of dislocations in the largest grains, or the least well oriented with respect to the bulk of the microstructure.

Lors de l'étape d'après, qui est la seconde étape du second type B', on abaisse à nouveau la température de l'alliage pour qu'il ait une température courante T4 inférieure à la température de transus β, Tβ, et on applique à nouveau une déformation plastique à l'alliage pour à nouveau créer de nouvelles contraintes mécaniques dans l'alliage et autour des grains en phase β.During the next step, which is the second step of the second type B', the temperature of the alloy is lowered again so that it has a current temperature T4 lower than the transus temperature β, Tβ, and a plastic deformation is again applied to the alloy to once again create new mechanical stresses in the alloy and around the grains in the β phase.

Comme cette étape B' est réalisée en dessous de la température de transus β, les phases α et β des grains en présence dans l'alliage sont conservées et seules des contraintes mécaniques sont générées autour des grains β les plus hétérogènes par rapport à la microstructure.As this step B' is carried out below the transus β temperature, the α and β phases of the grains present in the alloy are preserved and only mechanical stresses are generated around the most heterogeneous β grains with respect to the microstructure.

Lors de l'étape d'après, qui est la troisième étape du premier type C, on augmente à nouveau la température de l'alliage pour qu'il ait une température courante, dite troisième température T3, qui soit supérieure à la température de transus β, mais strictement inférieure à la seconde température T2 qui avait été atteinte lors de la seconde étape du premier type B. Lors de cette troisième étape du premier type C, les contraintes mécaniques accumulées, autour des grains β, lors de la seconde étape du second type B', génèrent à nouveau des ruptures / dislocations des grains β qui ont les plus grandes tailles et qui sont soumis aux plus grandes contraintes. L'effet de ces nouvelles dislocations est toujours de favoriser la recristallisation des grains β qui contiennent le plus de dislocations. L'alliage est ainsi à nouveau homogénéisé.During the next step, which is the third step of the first type C, the temperature of the alloy is increased again so that it has a current temperature, called the third temperature T3, which is higher than the temperature of transus β, but strictly lower than the second temperature T2 which had been reached during the second stage of the first type B. During this third stage of the first type C, the mechanical stresses accumulated, around the β grains, during the second stage of the second type B', again generate ruptures/dislocations of the β grains which have the largest sizes and which are subject to the greatest stresses. The effect of these new dislocations is always to promote the recrystallization of the β grains which contain the most dislocations. The alloy is thus homogenized again.

Le fait que les première, second et troisième étapes du premier type soient réalisées en abaissant progressivement la température tout en restant au-dessus de la température de transus β permet de créer progressivement des dislocations de plus en plus fines pour favoriser la précipitation des grains d'alliage en phase β les plus hétérogènes. Toutes ces étapes du procédé de conversion selon l'invention permettent d'homogénéiser la structure cristallographique de l'alliage tant au niveau de la répartition des grains de phases α et des grains de phase β dans l'alliage qu'au niveau des dimensions de ces grains respectifs.The fact that the first, second and third stages of the first type are carried out by gradually lowering the temperature while remaining above the transus temperature β makes it possible to gradually create increasingly finer dislocations to promote the precipitation of the grains d the most heterogeneous β-phase alloy. All these steps of the conversion process according to the invention make it possible to homogenize the crystallographic structure of the alloy both in terms of the distribution of the α phase grains and the β phase grains in the alloy and in terms of the dimensions of the alloy. these respective grains.

L'alliage ainsi converti présente des caractéristiques mécaniques plus homogènes ce qui permet d'homogénéiser les caractéristiques en fonction des directions envisagées des pièces métalliques obtenue à partir de cet alliage.The alloy thus converted has more homogeneous mechanical characteristics which makes it possible to homogenize the characteristics according to the envisaged directions of the metal parts obtained at from this alloy.

Dans un mode de réalisation préférentiel du procédé selon l'invention, on fait en sorte que :

  • la première température T1 soit supérieure à la température de transus β Tβ d'au moins 200°C et d'au plus 300°C ; que
  • la seconde température T2 soit supérieure à la température de transus β Tβ d'au moins 100°C et d'au plus 200°C ; et que
  • la troisième température T3 soit supérieure à la température de transus β Tβ d'au moins 50°C et d'au plus 150°C.
In a preferred embodiment of the method according to the invention, we ensure that:
  • the first temperature T1 is higher than the transus β temperature Tβ by at least 200°C and at most 300°C; that
  • the second temperature T2 is higher than the transus β temperature Tβ by at least 100°C and at most 200°C; and
  • the third temperature T3 is higher than the transus β temperature Tβ by at least 50°C and at most 150°C.

Le fait :

  • d'une part de limiter progressivement l'écart entre la température de transus β Tβ et les températures T1, T2, T3 successivement mises en oeuvre pour les première, seconde et troisième étapes du premier type A, B, C ; tout en s'assurant
  • d'autre part de ne pas dépasser une température limite Tlim au-dessus de la température de transus β Tβ;
    permet d'éviter le risque que des grains en phase β, voisins les uns des autres ne se recombinent en un seul gros grain en phase β, ce qui irait à l'encontre de l'effet recherché d'homogénéisation de l'alliage.
The fact :
  • on the one hand to progressively limit the difference between the transus temperature β Tβ and the temperatures T1, T2, T3 successively implemented for the first, second and third stages of the first type A, B, C; while ensuring
  • on the other hand not to exceed a limit temperature Tlim above the transus β temperature Tβ;
    makes it possible to avoid the risk that grains in the β phase, neighboring each other, recombine into a single large grain in the β phase, which would go against the desired effect of homogenization of the alloy.

Selon l'invention, on fait en sorte que chaque déformation plastique mise en oeuvre lors d'une étape du second type A', B', C' est telle qu'elle tend à inverser au moins partiellement l'effet de déformation appliquée à l'alliage lors de l'étape du premier type précédant immédiatement cette étape du second type.According to the invention, we ensure that each plastic deformation implemented during a step of the second type A', B', C' is such that it tends to at least partially reverse the effect of deformation applied to the alloy during the step of the first type immediately preceding this step of the second type.

Par inversion d'effet de déformation, on entend une inversion d'au moins une des déformations subies par l'alliage. Ainsi, si une première déformation a conduit à une diminution de la longueur de la billette composée de l'alliage, alors la déformation inversant l'effet de cette première déformation doit être réalisée de manière à obtenir une augmentation de la longueur de la billette.By reversal of deformation effect is meant a reversal of at least one of the deformations undergone by the alloy. Thus, if a first deformation led to a reduction in the length of the billet composed of the alloy, then the deformation reversing the effect of this First deformation must be carried out in such a way as to obtain an increase in the length of the billet.

En inversant, lors d'une étape du second type A', B', C', l'effet de la déformation appliquée lors de l'étape précédente du premier type A, B ou C, on augmente la capacité de déformation pouvant être mise en oeuvre lors d'une étape du premier type ultérieure. En effet, si l'on ne réalisait pas une déformation inversant au moins partiellement l'effet de la déformation réalisée lors d'une étape du premier type, on aurait alors une capacité de déformation de l'alliage beaucoup plus limitée lors de l'étape du premier type suivante. En effet, les déformations réalisées entre deux étapes successives du premier type A, B, C s'additionneraient jusqu'à atteindre une déformation telle qu'elle conduit à une rupture complète locale de l'alliage.By reversing, during a step of the second type A', B', C', the effect of the deformation applied during the previous step of the first type A, B or C, we increase the deformation capacity that can be implemented during a subsequent step of the first type. Indeed, if we did not carry out a deformation at least partially reversing the effect of the deformation carried out during a step of the first type, we would then have a much more limited deformation capacity of the alloy during the next step of the first type. Indeed, the deformations carried out between two successive stages of the first type A, B, C would add up until reaching a deformation such that it leads to a complete local rupture of the alloy.

En conséquence, l'inversion de l'effet de déformation permet de limiter les effets délétères associés aux multiples déformations réalisées durant les étapes du premier type.Consequently, the reversal of the deformation effect makes it possible to limit the deleterious effects associated with the multiple deformations carried out during the stages of the first type.

Selon l'invention, chacune des déformations plastiques mises en oeuvre lors des étapes du premier type sont des déformations par compression de l'alliage suivant une direction de compression d'alliage commune à toutes les étapes du premier type, ces déformations plastiques mises en oeuvre lors des étapes du premier type ont chacune un effet de réduction de la longueur Lx de l'alliage.According to the invention, each of the plastic deformations implemented during the stages of the first type are deformations by compression of the alloy following a direction of alloy compression common to all the stages of the first type, these plastic deformations implemented during the steps of the first type each have an effect of reducing the length Lx of the alloy.

La longueur Lx de l'alliage est la plus grande dimension de l'alliage ou du bloc d'alliage soumis à une déformation. Que l'alliage soit sous forme de lingot ou billette, cette longueur Lx d'alliage reste toujours la plus grande dimension mesurable sur cet alliage et cette longueur Lx est donc une longueur courante de l'alliage mesurée avant de faire subir à l'alliage une nouvelle étape de déformation.The length Lx of the alloy is the largest dimension of the alloy or block of alloy subjected to deformation. Whether the alloy is in the form of an ingot or billet, this alloy length Lx always remains the largest measurable dimension on this alloy and this length Lx is therefore a common length of the alloy measured before subjecting the alloy to a new stage of deformation.

Ainsi, lors des étapes du premier type, on tend à compacter l'alliage en en réduisant sa dimension courante Lx la plus importante la déformation. Ce type de déformation réalisée à température supérieure à Tβ est moins fragilisante qu'une déformation tendant à étirer l'alliage.Thus, during the stages of the first type, we tend to compact the alloy by reducing its current dimension Lx, the largest deformation. This type of deformation carried out at a temperature above Tβ is less weakening than a deformation tending to stretch the alloy.

Selon l'invention, chacune des déformations plastiques mise en oeuvre lors des étapes du second type A', B', C' sont des déformations par compression de l'alliage orientées de manière à obtenir à chaque étape du second type une augmentation de la longueur (Lx) de l'alliage.According to the invention, each of the plastic deformations implemented during the steps of the second type A', B', C' are deformations by compression of the alloy oriented so as to obtain at each step of the second type an increase in the length (Lx) of the alloy.

Typiquement, les déformations plastiques mises en oeuvre lors des opérations du deuxième type sont obtenues en comprimant l'alliage selon des directions de compression perpendiculaires à la direction de compression d'alliage commune à toutes les étapes du premier type.Typically, the plastic deformations implemented during operations of the second type are obtained by compressing the alloy in compression directions perpendicular to the alloy compression direction common to all stages of the first type.

BREVE DESCRIPTION DES DESSINSBRIEF DESCRIPTION OF THE DRAWINGS

D'autres caractéristiques et avantages de l'invention ressortiront clairement de la description qui en est faite ci-après, à titre indicatif et nullement limitatif, en référence aux dessins de la figure 1 qui illustre le procédé selon l'invention.Other characteristics and advantages of the invention will emerge clearly from the description given below, for information only and in no way limiting, with reference to the drawings of the invention. figure 1 which illustrates the process according to the invention.

DESCRIPTION DETAILLEE DE L'INVENTIONDETAILED DESCRIPTION OF THE INVENTION

Le procédé selon l'invention a pour but de permettre une conversion d'un alliage de titane se présentant au départ sous forme de lingot, ce procédé de conversion permettant d'homogénéiser les caractéristiques micro-structurelles de l'alliage.The purpose of the process according to the invention is to enable the conversion of a titanium alloy initially in the form of an ingot, this conversion process making it possible to homogenize the micro-structural characteristics of the alloy.

L'alliage converti suivant le procédé de conversion selon l'invention se présente sous la forme d'une ou plusieurs billettes. L'alliage ainsi obtenu se présente sous forme de billette et est alors successivement :

  • forgé pour générer des formes particulières nécessaires à la pièce finale qui est préférentiellement une grosse pièce d'atterrisseur comme une tige ou un bogie ; puis
  • usinée pour retirer une partie de l'alliage présent sur la pièce forgée ; puis éventuellement
  • mis en solution et trempé à l'eau ou l'air ;puis
  • vieilli thermiquement pour être durci, l'alliage ainsi vieilli étant un alliage quasi β contenant des nodules d'alliage en phase alpha primaire entre les grains β, ainsi qu'une précipitation de alpha secondaire à l'intérieur des grains β.
The alloy converted according to the conversion process according to the invention is in the form of one or more billets. The alloy thus obtained is in the form of a billet and is then successively:
  • forged to generate particular shapes necessary for the final part which is preferably a large undercarriage part such as a rod or a bogie; Then
  • machined to remove some of the alloy present on the forging; then possibly
  • put into solution and quenched with water or air; then
  • thermally aged to be hardened, the alloy thus aged being a quasi β alloy containing nodules of primary alpha phase alloy between the β grains, as well as a precipitation of secondary alpha inside the β grains.

Bien que l'invention concerne essentiellement le procédé de conversion selon l'invention, elle concerne également un procédé de production de pièce telle qu'une tige un bogie ou un caisson d'atterrisseur d'aéronef, ou toute pièce de taille comparable à une tige d'atterrisseur (longueur supérieure à 1 mètre), fabriquée à partir d'un alliage converti conformément au procédé de conversion d'alliage selon l'invention.Although the invention essentially relates to the conversion process according to the invention, it also relates to a process for producing a part such as a rod, a bogie or an aircraft landing box, or any part of a size comparable to a undercarriage rod (length greater than 1 meter), made from an alloy converted in accordance with the alloy conversion process according to the invention.

Ce procédé de production comporte, outre le procédé de conversion d'alliage selon l'invention, des étapes ultérieures précitées de forgeage, d'usinage et de vieillissement pour obtenir une grosse pièce d'atterrisseur quasi finie, comme une tige, un bogie, un caisson d'atterrisseur.This production process comprises, in addition to the alloy conversion process according to the invention, the aforementioned subsequent stages of forging, machining and aging to obtain a large, almost finished undercarriage part, such as a rod, a bogie, a landing box.

La présente description va maintenant présenter le procédé de conversion selon l'invention.The present description will now present the conversion method according to the invention.

La première étape du procédé de conversion selon l'invention consiste à produire un alliage comportant, en pourcentage massique de l'alliage, majoritairement du titane. Cet alliage est choisi pour présenter une température de transus β Tβ comprise entre 800°C et 950°C et préférentiellement de 900°C.The first step of the conversion process according to the invention consists of producing an alloy comprising, as a mass percentage of the alloy, predominantly titanium. This alloy is chosen to have a β Tβ transus temperature of between 800°C and 950°C and preferably 900°C.

Plus particulièrement, cet alliage est choisi dans le groupe d'alliages comprenant :
- un premier alliage (Ti 10-2-3) comportant, en proportion massique, les éléments suivants : Aluminium, Al 2.6 - 3.4 % Carbone, C <= 0.050 % Hydrogène H <= 0.015 % Fer, Fe 1.6 - 2.2 % Azote, N <= 0.050 % Oxygène, O <= 0.13 % Titane, Ti 83 - 86.8 % Vanadium, V 9.0 - 11 % ;
- un second alliage de type (Ti 5-5-5-3) comportant, en proportion massique, les éléments suivants : Fer Fe 0.5 - 1.5% Carbone C maximum 0.1% Silicium Si maximum 0.15% Chrome Cr 0.5 - 1.5% Molybdène Mo 4 - 5.5% Vanadium V 4 - 5.5% Azote N maximum 0.05% Titane Ti 79.4 - 86.3% Aluminium Al 4.4% - 5.7% Zirconium Zr maximum 0.3% Oxygène O maximum 0.18% Hydrogène H maximum 0.15% Impuretés 0.3%;
- un troisième alliage de type (Ti 5-5-5-3-1) comportant, en proportion massique, les éléments suivants : Fer Fe 0.5 - 1.5% Carbone C maximum 0.1% Silicium Si maximum 0.15% Chrome Cr 0.5 - 1.5% Molybdène Mo 4 - 5.5% Vanadium V 4 - 5.5% Azote N maximum 0.05% Titane Ti 79.4 - 86.3% Aluminium Al 4.4% - 5.7% Zirconium Zr 1% Oxygène O maximum 0.18% Hydrogène H maximum 0.15% Impuretés 0.3%;
- un quatrième alliage de type (Ti18) décrit dans le document brevet GB2470613A , et comportant, en proportion massique, les éléments suivants : Aluminium 5.3-5.7 % Vanadium V 4.8-5.2 % Fer Fe 0.7-0.9 % Molybdène Mo 4.6-5.3 % Chrome Cr 2.0-2.5 % Oxygène O 0.12-0.16 % le reste étant au moins du Titane et de impuretés ;
- un cinquième alliage comportant, en proportion massique, les éléments suivants : Titane au moins 84% Aluminium Al 4%-7.5% Oxygène au moins 0,1% Carbone C au moins 0,01% au moins un élément choisi parmi le vanadium, le molybdène, le chrome ou le fer, ce cinquième alliage comportant également du Hafnium et du Zirconium en addition dans une proportion massique d'au moins 0,1%.More particularly, this alloy is chosen from the group of alloys comprising:
- a first alloy (Ti 10-2-3) comprising, in mass proportion, the following elements: Aluminum, Al 2.6 - 3.4% Carbon, C <= 0.050% Hydrogen H <= 0.015% Iron, Fe 1.6 - 2.2% Nitrogen, N <= 0.050% Oxygen, O <= 0.13% Titanium, Ti 83 - 86.8% Vanadium, V 9.0 - 11%;
- a second type alloy (Ti 5-5-5-3) comprising, in mass proportion, the following elements: Iron Fe 0.5 - 1.5% Carbon C maximum 0.1% Silicon Si maximum 0.15% Chromium Cr 0.5 - 1.5% Molybdenum Mo 4 - 5.5% Vanadium V 4 - 5.5% Nitrogen N maximum 0.05% Titanium Ti 79.4 - 86.3% Aluminum Al 4.4% - 5.7% Zirconium Zr maximum 0.3% Oxygen O maximum 0.18% Hydrogen H maximum 0.15% Impurities 0.3%;
- a third type alloy (Ti 5-5-5-3-1) comprising, in mass proportion, the following elements: Iron Fe 0.5 - 1.5% Carbon C maximum 0.1% Silicon Si maximum 0.15% Chromium Cr 0.5 - 1.5% Molybdenum Mo 4 - 5.5% Vanadium V 4 - 5.5% Nitrogen N maximum 0.05% Titanium Ti 79.4 - 86.3% Aluminum Al 4.4% - 5.7% Zirconium Zr 1% Oxygen O maximum 0.18% Hydrogen H maximum 0.15% Impurities 0.3%;
- a fourth type alloy (Ti18) described in the patent document GB2470613A , and comprising, in mass proportion, the following elements: Aluminum 5.3-5.7% Vanadium V 4.8-5.2% Iron Fe 0.7-0.9% Molybdenum Mo 4.6-5.3% Chromium Cr 2.0-2.5% Oxygen O 0.12-0.16% the remainder being at least Titanium and impurities;
- a fifth alloy comprising, in mass proportion, the following elements: Titanium at least 84% Aluminum Al 4%-7.5% Oxygen at least 0.1% Carbon C at least 0.01% at least one element chosen from vanadium, molybdenum, chromium or iron, this fifth alloy also comprising Hafnium and Zirconium in addition in a mass proportion of at least 0.1%.

Le cinquième alliage est particulièrement adapté pour être converti à l'aide du procédé selon l'invention car il présente une température de transus β, Tβ, comprise entre 800°C et 950°C et plus particulièrement une température de transus β, Tβ=900°C.The fifth alloy is particularly suitable for being converted using the process according to the invention because it has a transus β temperature, Tβ, between 800°C and 950°C and more particularly a transus β temperature, Tβ= 900°C.

Plus particulièrement, ce cinquième alliage, comporte, en proportion massique, au moins 84% de Titane et au moins les éléments suivants : - Aluminium 4,0 - 7,5% - Vanadium 3,5 - 5,5% - Molybdène 4,5-7,5% - Chrome 1,8-3,6% - Fer 0,2-0,5% - Hafnium 0,1-1,1% - Oxygène 0,1-0,3% - Carbone 0,01-0,2%. More particularly, this fifth alloy, contains, in mass proportion, at least 84% Titanium and at least the following elements: - Aluminum 4.0 - 7.5% - Vanadium 3.5 - 5.5% - Molybdenum 4.5-7.5% - Chromium 1.8-3.6% - Iron 0.2-0.5% - Hafnium 0.1-1.1% - Oxygen 0.1-0.3% - Carbon 0.01-0.2%.

Chacun de ces alliages de titane présente une température de transus β Tβ qui lui est propre.Each of these titanium alloys has its own transus temperature β Tβ.

Typiquement, la température du cinquième alliage préférentiel est de Tβ= 900°C.Typically, the temperature of the fifth preferential alloy is Tβ=900°C.

Comme indiqué précédemment, la température de transus β est la température à partir de laquelle on observe une transition de structures de l'alliage en phase α vers des structures de l'alliage en phase β.As indicated previously, the β transus temperature is the temperature from which a transition from α-phase alloy structures to β-phase alloy structures is observed.

L'alliage ainsi produit est coulé pour fabriquer un lingot 1 composé dudit alliage.The alloy thus produced is cast to manufacture an ingot 1 composed of said alloy.

Comme on le voit sur la figure 1, le procédé de conversion selon l'invention comporte :

  • au moins des première, seconde et troisième étapes d'un premier type A, B, C consistant à déformer plastiquement l'alliage issu dudit lingot alors qu'il est à une température courante strictement supérieure à la température de transus β Tβ et inférieure à une température limite Tlim = TP+300°C; et
  • au moins des première et seconde étapes d'un second type A', B' consistant à déformer plastiquement l'alliage issu dudit lingot alors qu'il est à une température courante strictement inférieure à la température de transus β Tβ.
As seen on the figure 1 , the conversion method according to the invention comprises:
  • at least first, second and third steps of a first type A, B, C consisting of plastically deforming the alloy from said ingot while it is at a current temperature strictly greater than the transus temperature β Tβ and less than a limit temperature Tlim = TP+300°C; And
  • at least first and second steps of a second type A', B' consisting of plastically deforming the alloy from said ingot while it is at a current temperature strictly lower than the transus temperature β Tβ.

Dans le cas présent, le procédé comporte une troisième étape du second type C'.In the present case, the process comprises a third step of the second type C'.

Ces étapes des premier et second types A, A', B, B', C sont mises en oeuvre pour une même portion de l'alliage en suivant la séquence consistant en :

  • réalisation de la première étape du premier type A alors que l'alliage se trouve à une première température T1; puis
  • réalisation de la première étape du second type A' alors que l'alliage se trouve à une température T4, dite quatrième température; puis
  • réalisation de la seconde étape du premier type B alors que l'alliage se trouve à une seconde température T2 strictement inférieure à ladite première température T1; puis
  • réalisation de la seconde étape du second type B' alors que l'alliage est à T4; puis
  • réalisation de la troisième étape du premier type C alors que l'alliage se trouve à une troisième température T3 strictement inférieure à ladite seconde température T2 ; puis
  • réalisation de la troisième étape du second type C' alors que l'alliage est à T4.
These steps of the first and second types A, A', B, B', C are implemented for the same portion of the alloy following the sequence consisting of:
  • carrying out the first step of the first type A while the alloy is at a first temperature T1; Then
  • carrying out the first step of the second type A' while the alloy is at a temperature T4, called the fourth temperature; Then
  • carrying out the second step of the first type B while the alloy is at a second temperature T2 strictly lower than said first temperature T1; Then
  • carrying out the second step of the second type B' while the alloy is at T4; Then
  • carrying out the third step of the first type C while the alloy is at a third temperature T3 strictly lower than said second temperature T2; Then
  • completion of the third step of the second type C' while the alloy is at T4.

Typiquement, on a T1 défini par (Tβ + 200°C) <T1< (Tβ+300°C) ; T2 défini par T2<T1 et (Tβ + 100°C) <T2< (Tβ + 200°C) ; T3 défini par T3<T2<T1 et (Tβ + 50°C) <T3< (Tβ + 150°C) ; T4 qui est la quatrième température mise en oeuvre à chacune des étapes du second type est définie par (Tβ-65°C)<T4<(Tβ-35°C) ou préférentiellement par (Tβ-55°C)<T4<(Tβ-45°C). En d'autres termes chacune des étapes du second type est mise en oeuvre à la quatrième température T4 comprise entre la température de transus β (Tβ) moins 50°C à plus ou moins 15°C près et préférentiellement à plus ou moins 5°C près. Dans le cas de la figure 1, Tβ=800°C, T1=1100°C, T2=1000°C, T3=900°C, T4=750°C.Typically, we have T1 defined by (Tβ + 200°C) <T1<(Tβ+300°C); T2 defined by T2<T1 and (Tβ + 100°C) <T2< (Tβ + 200°C); T3 defined by T3<T2<T1 and (Tβ + 50°C) <T3< (Tβ + 150°C); T4 which is the fourth temperature used at each of the stages of the second type is defined by (Tβ-65°C)<T4<(Tβ-35°C) or preferably by (Tβ-55°C)<T4<( Tβ-45°C). In other words each of the steps of the second type is implemented at the fourth temperature T4 between the transus temperature β (Tβ) minus 50°C to plus or minus 15°C and preferably to plus or minus 5° C close. In the case of the figure 1 , Tβ=800°C, T1=1100°C, T2=1000°C, T3=900°C, T4=750°C.

Ces températures T1, T2, T3, T4 sont vérifiées si elles sont entre +/-15°C de la température indiquée et préférentiellement entre +/-5°C de cette température. Le choix de la quatrième température T4 permet de conserver les phases α et β en présence dans l'alliage sans trop accumuler de contraintes autour des grains β.These temperatures T1, T2, T3, T4 are checked if they are between +/-15°C of the indicated temperature and preferably between +/-5°C of this temperature. The choice of the fourth temperature T4 makes it possible to keep the α and β phases present in the alloy without accumulating too much stress around the β grains.

Bien que l'on ait décrit que les températures auxquelles sont mises en oeuvre les étapes du second type A', B', C' sont identiques, il est possible qu'elles diffèrent entre elles.Although it has been described that the temperatures at which the steps of the second type A', B', C' are carried out are identical, it is possible that they differ from each other.

Avant la première étape du premier type A, le lingot 1 formé de l'alliage présente une longueur courante Lx définissant un axe principal X-X de l'alliage.Before the first step of the first type A, the ingot 1 formed from the alloy has a current length Lx defining a main axis X-X of the alloy.

Dans toutes les étapes du premier type, A, B, C, la direction de compression d'alliage est orientée parallèlement à cet axe principal d'alliage, et plus particulièrement parallèlement à cette longueur du lingot.In all stages of the first type, A, B, C, the direction of alloy compression is oriented parallel to this main alloy axis, and more particularly parallel to this length of the ingot.

Les directions de compression de l'alliage qui sont mises en oeuvre lors des étapes du second type A', B', C' sont perpendiculaires à la longueur du lingot, c'est-à-dire perpendiculaires à l'axe principal X-X.The directions of compression of the alloy which are implemented during the steps of the second type A', B', C' are perpendicular to the length of the ingot, that is to say perpendicular to the main axis X-X.

Typiquement, les compressions mises en oeuvre lors des étapes du premier type A, B, C sont réalisées en plaçant le lingot entre des éléments d'une presse se rapprochant l'un de l'autre suivant une direction parallèle à la longueur du lingot.Typically, the compressions implemented during the steps of the first type A, B, C are carried out by placing the ingot between elements of a press approaching each other in a direction parallel to the length of the ingot.

Typiquement, les compressions mises en oeuvre lors des étapes du deuxième type A', B', C' sont obtenues par écrasement de l'alliage entre des outils de forme ou non placés en vis-à-vis pour entraîner une réduction de section de l'alliage et ainsi un allongement progressif de l'alliage. La déformation réalisée au cours de la première étape du premier type A comprend au moins une opération de refoulement R réduisant la longueur Lx de l'alliage de 20 à 30% de la longueur Lx d'alliage mesurée avant mise en oeuvre de cette première étape du premier type A.Typically, the compressions implemented during the steps of the second type A', B', C' are obtained by crushing the alloy between shaped or non-shaped tools placed opposite each other to cause a reduction in section of the alloy and thus a progressive elongation of the alloy. The deformation carried out during the first step of the first type A comprises at least one upsetting operation R reducing the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured before implementation of this first step of the first type A.

La déformation réalisée au cours de la seconde étape du premier type B comprend également une opération de refoulement R réduisant la longueur Lx de l'alliage de 20 à 30% de la longueur Lx d'alliage mesurée après mise en oeuvre de la première étape du second type A' et avant mise en oeuvre de la seconde étape du premier type B.The deformation carried out during the second step of the first type B also includes an upsetting operation R reducing the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured after implementation of the first step of the second type A' and before implementation work of the second stage of the first type B.

La déformation réalisée au cours de la troisième étape du premier type C comprend aussi un refoulement R réduisant la longueur Lx de l'alliage de 15 à 20% de la longueur Lx d'alliage mesurée après mise en oeuvre de la seconde étape du second type B' et avant mise en oeuvre de la troisième étape du premier type C.The deformation carried out during the third stage of the first type C also includes an upsetting R reducing the length Lx of the alloy by 15 to 20% of the length Lx of the alloy measured after implementation of the second stage of the second type B' and before implementation of the third step of the first type C.

Le refoulement R est une opération de compression de l'alliage selon sa longueur Lx, c'est-à-dire selon l'axe X-X de l'alliage.The upsetting R is an operation of compression of the alloy along its length Lx, that is to say along the axis X-X of the alloy.

La déformation E1 réalisée au cours de la première étape du second type A' est réalisée pour augmenter la longueur Lx de l'alliage de 20 à 30% de la longueur Lx d'alliage mesurée après mise en oeuvre de la première étape du premier type A et avant cette augmentation de longueur Lx mise en oeuvre de la première étape du second type A'.The deformation E1 carried out during the first step of the second type A' is carried out to increase the length Lx of the alloy from 20 to 30% of the length Lx of the alloy measured after implementation of the first step of the first type A and before this increase in length Lx implementation of the first step of the second type A'.

La déformation E4 réalisée au cours de la seconde étape du second type B' est adaptée à augmenter la longueur Lx de l'alliage de 20 à 30% de la longueur Lx d'alliage mesurée après mise en oeuvre de la seconde étape du premier type B et avant l'augmentation de longueur Lx réalisée lors de cette seconde étape du second type B'.The deformation E4 carried out during the second step of the second type B' is adapted to increase the length Lx of the alloy by 20 to 30% of the length Lx of the alloy measured after implementation of the second step of the first type B and before the increase in length Lx carried out during this second step of the second type B'.

Postérieurement à la troisième étape du premier type C, on met en oeuvre une troisième étape du second type C', cette troisième étape C' permet de donner à l'alliage une forme et des dimensions propres à son forgeage ultérieur pour l'obtention d'une pièce forgée.After the third step of the first type C, a third step of the second type C' is implemented, this third step C' makes it possible to give the alloy a shape and dimensions suitable for its subsequent forging to obtain 'a forged part.

Cette troisième étape du second type C' peut être adaptée à augmenter la longueur Lx de l'alliage d'au moins 30% de la longueur Lx d'alliage Lx mesurée après mise en oeuvre de la troisième étape du premier type C et avant mise en oeuvre de cette augmentation de longueur Lx réalisée à la troisième étape du second type C'.This third step of the second type C' can be adapted to increase the length Lx of the alloy by at least 30% of the length Lx of the alloy Lx measured after implementation of the third step of the first type C and before implementation of this increase in length Lx carried out in the third step of the second type C'.

On note que postérieurement à la seconde étape du premier type B et avant la troisième étape du second type C', de préférence entre les étapes B' et C, on met en oeuvre une étape de découpe X selon un plan transversal de l'alliage de manière à obtenir deux parties allongées en forme de barres nommées billettes 1', 1''.Note that after the second step of the first type B and before the third step of the second type C', preferably between steps B' and C, a cutting step X is carried out along a transverse plane of the alloy so as to obtain two elongated bar-shaped parts called billets 1', 1''.

Idéalement, ces parties/billettes 1', 1" sont de formes identiques entre elles. La forme d'une billette destinée à former une grosse pièce d'atterrisseur d'aéronef est sensiblement cylindrique droite de longueur comprise entre 2 m et 3 m et de diamètre compris entre 0.4 et 0.5 m.Ideally, these parts/billets 1', 1" are of identical shapes to each other. The shape of a billet intended to form a large part of an aircraft undercarriage is substantially straight cylindrical with a length of between 2 m and 3 m and with a diameter of between 0.4 and 0.5 m.

A l'origine, le lingot d'alliage, avant mise en oeuvre de la première étape du premier type A est de forme cylindrique droite de longueur comprise entre 3m et 5m et de diamètre compris entre 0.6 m et 1.2 m .Originally, the alloy ingot, before implementation of the first stage of the first type A, is of right cylindrical shape with a length of between 3m and 5m and a diameter of between 0.6m and 1.2m.

Le volume de deux billettes 1', 1" est inférieur au volume du lingot ce qui implique qu'une partie de l'alliage a été évacuée lors des différentes étapes du procédé de conversion d'alliage selon l'invention.The volume of two billets 1', 1" is less than the volume of the ingot, which implies that part of the alloy was evacuated during the different stages of the alloy conversion process according to the invention.

Dans le cas présent :

  • à l'étape A, on réalise une opération de refoulement R1 suivie d'une opération d'étirage E1 ;
  • à l'étape A', on réalise une opération de refoulement R2 suivie d'une opération d'étirage E2 ;
  • à l'étape B, on réalise une opération de refoulement R3 suivie d'une opération d'étirage E3 ;
  • à l'étape B', on réalise une opération de refoulement R4 suivie d'une opération d'étirage E4 ;
  • à l'étape C, on réalise une opération de refoulement R5 suivie d'une opération d'étirage E5 ;
  • à l'étape C', on réalise une opération de refoulement R6 suivie d'une opération d'étirage E6 qui conduit à la billette 1' finie et prête à être forgée.
In the present case :
  • in step A, a pressing operation R1 is carried out followed by a stretching operation E1;
  • in step A', a pressing operation R2 is carried out followed by a stretching operation E2;
  • in step B, a pressing operation R3 is carried out followed by a stretching operation E3;
  • in step B', a pressing operation R4 is carried out followed by a stretching operation E4;
  • in step C, an upsetting operation R5 is carried out followed by a stretching operation E5;
  • in step C', a pushing operation R6 is carried out followed by a stretching operation E6 which leads to the billet 1' finished and ready to be forged.

Ces étirements E1, E2, E3, E4, E5, E6 sont des allongements de la longueur courante d'alliage Lx obtenus par compression latérale de l'alliage et non par traction.These stretchings E1, E2, E3, E4, E5, E6 are extensions of the current alloy length Lx obtained by lateral compression of the alloy and not by traction.

La billette 1' issue du procédé est formée d'un alliage converti dont la microstructure est homogénéisée au moins en terme de dimensions de grains en phase β et de répartition de ces grains dans l'alliage par rapport à la microstructure observée avant mise en oeuvre de l'étape A du procédé.The billet 1' resulting from the process is formed of a converted alloy whose microstructure is homogenized at least in terms of grain dimensions in β phase and distribution of these grains in the alloy compared to the microstructure observed before implementation of step A of the process.

Bien que le procédé selon l'invention ait été présenté avec trois étapes du premier type et trois étapes du second type, on note qu'il peut aussi comporter un plus grand nombre d'étapes du premier type et un plus grand nombre d'étapes du second type.Although the process according to the invention has been presented with three steps of the first type and three steps of the second type, it should be noted that it can also include a larger number of steps of the first type and a larger number of steps of the second type.

Quel que soit le nombre d'étapes du second type mises en oeuvre on fait préférentiellement en sorte que l'on ait au moins une étape du second type mise en oeuvre entre deux étapes successives du premier type.Whatever the number of steps of the second type implemented, we preferably ensure that we have at least one step of the second type implemented between two successive steps of the first type.

Claims (12)

  1. A method of converting an alloy that comprises, in percentage by weight of alloy, a majority of titanium, the alloy presenting a β transus temperature beyond which a transition is observed from α phase alloy structures to β phase alloy structures, the method comprising:
    · a step of fabricating an ingot (1) made of said alloy;
    · at least first, second, and third steps of a first type (A, B, C) consisting in plastically deforming the alloy from said ingot while it is at a current temperature strictly higher than the β transus temperature (Tβ); and
    · at least first and second steps of a second type (A', B') consisting in plastically deforming the alloy from said ingot while it is at a current temperature strictly lower than the β transus temperature (Tβ) to maintain the α and β phases present in the alloy, wherein these steps of the first and second types (A, A', B, B', C) are applied in the following sequence consisting in :
    · performing the first step of the first type (A) while the alloy is at a first temperature (T1); followed by
    · performing the first step of the second type (A'); followed by
    · performing the second step of the first type (B) while the alloy is at a second temperature (T2) strictly lower than said first temperature (T1); followed by
    · performing the second step of the second type (B'); followed by
    · performing the third step of the first type (C) while the alloy is at a third temperature (T3) strictly lower than said second temperature (T2) characterized in that each plastic deformation performed during a step of the second type (A', B') is such as to tend to reverse at least in part the effect of the deformation applied to the alloy during the step of the first type preceding said step of the second type and wherein;
    - each of the plastic deformation operations performed during the steps of the first type are operations of deformation by compressing the alloy in an alloy compression direction that is common to all of the steps of the first type, each of these plastic deformation operations during the steps of the first type having an effect of shortening the length (Lx) of the alloy, the length (Lx) of the alloy being the greatest dimension of the alloy or of the block of alloy submitted to a deformation; and wherein
    - each of the plastic deformation operations performed during the steps of the second type are operations of deforming the alloy by compression oriented in such a manner as to obtain on each step of the second type an increase in the length (Lx) of the alloy.
  2. An alloy conversion method according to claim 1, wherein:
    · the first temperature (T1) is higher than the β transus temperature (Tβ) by at least 200°C and at most 300°C;
    · the second temperature (T2) is higher than the β transus temperature (Tβ) by at least 100°C and at most 200°C;
    · the third temperature (T3) is higher than the β transus temperature (Tβ) by at least 50°C and at most 150°C.
  3. An alloy conversion method according to anyone of claims 1 or 2, wherein the deformation (R1) performed during the first step of the first type (A) is adapted to shorten the length (Lx) of the alloy by 20% to 30% of the length (Lx) of the alloy measured before performing this first step of the first type (A).
  4. A conversion method according to claim 3, wherein the deformation (R3) performed during the second step of the first type (B) is adapted to shorten the length (Lx) of the alloy by 20% to 30% of the length (Lx) of the alloy measured after performing this first step of the second type (A') and before performing this second step of the first type (B).
  5. A conversion method according to at least one of claims 3 or 4, wherein the deformation (R5) performed during the third step of the first type (C) is adapted to shorten the length (Lx) of the alloy by 15% to 20% of the length (Lx) of the alloy measured after performing the second step of the second type (B') and before performing this third step of the first type (C).
  6. A conversion method according to at least one of claims 3 to 5, wherein the deformation (E2) performed during the first step of the second type (A') is adapted to increase the length (Lx) of the alloy by 20% to 30% of the length (Lx) of the alloy measured after performing the first step of the first type (A) and before increasing the length (Lx) during this first step of the second type (A').
  7. A conversion method according to claim 6, wherein the deformation (E4) performed during the second step of the second type (B') is adapted to increase the length (Lx) of the alloy by 20% to 30% of the length (Lx) of the alloy measured after performing the second step of the first type (B) and before increasing the length (Lx) during this second step of the second type (B').
  8. An alloy conversion method according to at least one of claims 1 to 7, wherein after the first step of the first type (C), a third step of the second type (C') is performed.
  9. An alloy conversion method according to claim 8, wherein after the second step of the first type (B) and before the third step of the second type (C'), a cutting step is performed on a transverse plane of the alloy so as to obtain two elongate portions in the form of bars referred to as billets.
  10. A conversion method according to any preceding claim, wherein each of the steps of the second type is performed at a fourth temperature (T4) lying between the β transus temperature (Tβ) minus 50°C to within plus or minus 15°C, and preferably to within plus or minus 5°C.
  11. A method according to any one of claims 1 to 10, wherein the alloy is selected to present a β transus temperature (Tβ) lying in the range 800°C to 950°C, and preferably of 900°C.
  12. A method of production of an aircraft landing gear part, consisting in :
    - obtaining a converted alloy by performing the method of converting an alloy according to any one of claims 1 to 11, the converted alloy thus obtained having the shape of a billet, this billet of converted alloy being successively;
    - forged to generate particular shapes which are necessary to the aircraft landing gear part;
    - machined to withdraw a portion of the alloy of the forged part; and
    the alloy of the machined part thus obtained being subjected to solution heat treatment and quenched in water or air and then thermally aged in order to be hardened, the alloy as aged in this way being a quasi-β alloy containing nodules of primary alpha phase alloy between the β grains, together with a precipitate of secondary alpha inside the β grains.
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