EP1340832B1 - Thin products made of beta or quasi beta titanium alloys, manufacture by forging - Google Patents

Description

The subject of the present invention is thin products made of β or quasi-β titanium alloys, as well as the manufacture by forging of said thin products.

• des produits manufacturés, non axisymétriques, d'une épaisseur inférieure à 10 mm, en alliages de titane β ou quasi β, qui présentent une microstructure originale ;
• un procédé pour la fabrication desdits produits qui, de façon caractéristique, est basé sur une opération de forgeage.

It concerns more precisely:

• non-axisymmetric manufactured products with a thickness of less than 10 mm in titanium alloys β or almost β, which have an original microstructure;
• a process for the manufacture of said products which typically is based on a forging operation.

The design and development context of the presently claimed invention has been that of the manufacture of monoblock bladed disks (DAM) with linear friction welding blades. Said monobloc bladed discs, with reference to their mechanical properties and in particular their resistance to vibratory fatigue, are generally made of a titanium β or quasi-β alloy. They are obtained, to date, by machining, in a massive crude.

Contrary to the obtaining by forging of the blades of such disks in a titanium alloy β or almost β, there was a real prejudice. The forging of structures made of titanium alloys β or quasi β, that is to say of coarse-grained structures, to develop parts of small thicknesses (blades), could lead a priori only to such parts, to mechanical properties (including shock resistance, vibration fatigue resistance) disappointing.

Surprisingly, in the context of the present invention, blades (thin products) made of titanium alloys β or almost β that perform well (having good metallurgical health and good mechanical properties) have been obtained by forging (FIG. that is to say with economy of material, compared to the machining technique, conventionally implemented). Said blades also have longer lifetimes than blades obtained by machining; they can also be obtained with optimized geometries, to improve the aerodynamics, so the performance of the engine in which they are likely to intervene.

EP-A-0 852 164 discloses a method for producing titanium alloy turbine blades which comprises a forging step followed by localized forced cooling of the leading edges of the tip portions of said blades. For α + β and quasi β alloys, the forging is carried out at a temperature of 10 ° C. or more below the temperature of β-transus.

US-A-4,854,977 describes a large smithing process, particularly suitable for obtaining compressor disks for aircraft propulsion systems. The forging operation used comprises roughing forging and final forging, advantageously started in β and finished in α-β.

The invention has therefore been conceived and developed, in a non-obvious manner, in the context of the manufacture of monobloc bladed disks (DAM). However, it is not limited to this context; it is also expressed, naturally, in more or less neighboring contexts, such as that of the manufacture of monoblock bladed rings (ANAM), those of the repair of said monoblock bladed discs (DAM) and bladed monoblock rings (ANAM), and more generally that of the manufacture of thin titanium products β or almost β.

Controlling the forging, according to the invention, of billets made of titanium alloys β or quasi β, of small thicknesses, made it possible to obtain thin products, in said titanium alloys β or almost β, which are original because of their microstructure. heart.

Said products constitute the first object of the present invention.

The controlled forging process that leads to said products constitutes the second object.

According to its first object, the present invention therefore relates to manufactured products, not axisymmetric (the son are thus excluded), a thickness of less than 10 mm (these 10 mm specify the concepts of "thin", "thin products" , used in the present text), in titanium alloys substantially β, the core microstructure consists of whole grains having a slenderness ratio greater than 4 and an equivalent diameter of between 10 and 300 microns.

Titanium alloys β or almost β (which can also be described as close β) are familiar to the skilled person. They have a compact hexagonal structure. They are perfectly defined, especially in American Handbooks (US): ASMH (AMERICAN SOCIETY MATERIAL HANDBOOK) and MILH (MILITARY HANDBOOK). Their use is, to date, confined to the manufacture of massive forgings or thick layers.

Typically, the manufactured products of the invention, in said alloys, are thin products that carry the heredity of their manufacturing process, based on one or more forging operations. Their microstructure at heart is original. The grains of said core microstructure have been wrought.

They have a slenderness ratio greater than 4; said slenderness ratio being conventionally defined as the ratio of the largest dimension to the smallest dimension in the axial section plane.

They have an equivalent diameter of between 10 and 300 microns.

In place of the large truncated grains found in the structure of equivalent (thin) products obtained by machining, whole grains, crushed, lenticular are found in the heart of the products of the invention.

The manufactured products of the invention, by the characteristics stated above, are new products. These new products are likely to be obtained by forging. As explained above, there was a real prejudice to seek thin structures by forging thicker coarse-grained structures and, quite surprisingly, such thin structures have been found to have very interesting characteristics.

The manufactured products of the invention advantageously consist of turbine engine compressor blades.

The invention is however not limited to this context. The products in question may also consist of propellers, including submarines, fan blades or mixers (capable of intervening in environments justifying the constitution of said blades β or quasi β titanium alloys). This list can not be exhaustive.

According to a particularly preferred variant (in no way limiting), the manufactured products of the invention are Ti ₁₇ alloy. This alloy, familiar to the skilled person, is used to date to make massive parts, including compressor discs. It has high flow constraints and is also known to be difficult to forge.

• TA₅CD₄, selon la nomenclature métallurgique,
• TAl₅Cr₂Mo₄, selon la nomenclature chimique.

It is more precisely the alloy:

• TA ₅ CD ₄ , according to the metallurgical nomenclature,
• TAl ₅ Cr ₂ Mo ₄ , according to the chemical nomenclature.

Surprisingly, the inventors have, in the context of the invention presently claimed, forged thin pieces, said Ti alloy ₁₇ , with significant wrought rates; said forgings having high mechanical properties.

We now come to the second object of the present invention, namely the method of manufacturing new products, according to claim 5.

The product to be forged is conventionally enamelled.

Said product is advantageously obtained by transformation of an enamelled billet. It generally consists of a half-product, obtained by spinning or forging a starting material, with a larger equivalent diameter (with a greater thickness). It may especially be a bar (having, for example, a diameter of 25 mm), obtained by spinning a billet. In fact, titanium alloys β or close β exist mainly in the form of such billets (intended for the manufacture of compression discs by machining).

This enamelled product, generally enamelled half product, of a diameter (equivalent) less than 100 mm, is, according to the invention, converted by forging into a manufactured product with a thickness of less than 10 mm.

• une première chaude en sub ou super transus β, généralement à une température comprise entre 700 et 1000°C ;
• une dernière chaude en super transus β, généralement à une température supérieure à 880°C.

To obtain such a manufactured product, with optimized properties, it is recommended the implementation of forging under the conditions below. The forging operation comprises at least two hot:

• a first hot sub or super β transus, generally at a temperature between 700 and 1000 ° C;
• a last hot in β super transus, usually at a temperature above 880 ° C.

The temperatures in question are obviously dependent on the alloy of Ti β or Ti quasi β concerned.

The reduction rate at each hot is greater than or equal to (advantageously greater than) 2 and the forging speeds (or crushing speeds) are between 1 and 1.10 ^-5 s ^-1 .

The forging operation can be quite limited to the two hot, as specified above (the second of said two hot is imperatively a hot super-transus It may include an additional hot, sub or super transus β, before the Last (third) hot in super transus β It is not totally excluded that it includes more than three hot (the last of these hot being imperatively a hot super transus β) but the interest to multiply the number of hot is not obvious.

The forging operation therefore generally includes two or three hot, implemented under the conditions specified above.

In a conventional manner, the forged product is optionally re-enamelled between two successive hot.

According to an advantageous variant embodiment, the forging die is maintained at a temperature of between 100 and 700 ° C.

The forging operation is conventionally followed by quenching (usually immediately followed by such quenching). Such quenching can in particular be carried out under pulsed air, in calm air, in an oil bath or on a matrix. It is advantageously used under conditions that induce a cooling rate that is less than or equal to that induced by quenching in an oil bath.

The tempered product of the forged product is advantageously used at a temperature of between 620 and 750 ° C. for 3 to 5 hours. Its implementation conditions are optimized according to the characteristics sought for the finished product. It is ensured to perform said income under an inert atmosphere (especially vacuum or argon) if the enameling is cracked or flaking.

• le produit long émaillé est en alliage Ti₁₇ (TA₅CD₄ ou TiAl₅Cr₂MO₄);
• le forgeage comprend une première chaude à une température inférieure ou égale à 840 ± 10°C (en sub transus β) ou à une température supérieure ou égale à 940 ± 10°C (en super transus β) et une seconde chaude à une température de 940 ± 10°C (en super transus β);
• la trempe est mise en oeuvre sur matrice puis à l'air calme ;
• le revenu est mis en oeuvre à 630°C pendant 4 h.

According to a particularly advantageous variant, the process of the invention is carried out under the following conditions:

• the long enamelled product is Ti ₁₇ alloy (TA ₅ CD ₄ or TiAl ₅ Cr ₂ MO ₄ );
• the forging comprises a first hot at a temperature less than or equal to 840 ± 10 ° C (in sub transus β) or at a temperature greater than or equal to 940 ± 10 ° C (super transus β) and a hot second at a temperature 940 ± 10 ° C (in β super transus);
• quenching is carried out on a matrix and then with calm air;
• the income is operated at 630 ° C for 4 hours.

It leads to a product, as described in the first part of this text, which can include a dawn.

The manufacture of such a blade is specified in the example below, given for purely illustrative purposes.

In Figures 1 and 2 attached, it shows, at different scales, the microstructure core - microstructure original - of such a blade.

In Figure 1 - section in the three directions: cross section along the plane A, longitudinal along the plane B and facial along the plane C; magnification: x 20 - the lenticular shape of the grains is clearly visible: strongly crushed in the transverse and longitudinal directions and having a large face in the facial section.

In Figure 2 - high magnification: x 5000 - the internal microstructure of the grains is shown. There is referenced 1 a hardened grain, 2 a recrystallized grain. The α needles are very thin and very entangled.

Example : Making a blade made of Ti ₁₇ by forging.

• filage d'une barre (φ < 100 mm) pour obtenir un lopin (φ : 27 mm) de 240 mm de long ;
• émaillage ;
• écrasement radial de la barre filée pour former la pale et le pied ;
• matrice de forgeage portée à 200°C ;
• vitesse de frappe (presse à vis) : 10^-4 s^-1 ;
• 1^ère chaude : le lopin émaillé, maintenu 45 min à 940°C (chaude en super transus β) est écrasé jusqu'à présenter une épaisseur de 13 à 8 mm.
• 2^ème chaude : conditions identiques à la 1^ère. Le nouvel écrasement génère une pièce dont l'épaisseur varie de 9 à 1 mm.
• refroidissement sur matrice puis par air calme sur table ;
• revenu direct après forge de 630°C/4 h.

The process used comprises the following successive stages:

• spinning a bar (φ <100 mm) to obtain a piece (φ: 27 mm) 240 mm long;
• enameling;
• radial crushing of the bar spun to form the blade and the foot;
• forging die heated to 200 ° C;
• typing speed (screw press): 10 ^-4 s ^-1 ;
• 1 hot ^era: the enamel piece, maintained 45 min at 940 ° C (hot super β transus) is crushed to have a thickness of 13-8 mm.
• ^2nd hot: conditions identical to the ^1st. The new crushing generates a piece whose thickness varies from 9 to 1 mm.
• cooling on a matrix then by calm air on a table;
• direct income after forging of 630 ° C / 4 h.

It generates a blade whose core microstructure is as shown in the accompanying figures.

Claims (11)

1. Non-axially symmetrical manufactured parts of quasi-β titanium alloy, characterized in that they show:

   - a thickness less than 10 mm, and

   - a core microstructure constituted by whole grains being lens-shaped and presenting a slenderness ratio greater than 4 and an equivalent diameter lying in the range 10 µm to 300 µm.
2. The manufactured parts according to claim 1, able to be obtained by forging.
3. The manufactured parts according to claim 1 or 2, consisting in blades for turbomachine compressors.
4. The manufactured parts according to any one of claims 1 to 3, made of Ti₁₇ alloy: TA₅CD₄ or TiAl₅Cr₂Mo₄.
5. A method of manufacturing a part according to any preceding claims, the method comprising successive steps of forging, quenching of the forged part and tempering of the said forged quenched part, characterized in that:

   - forging is carried out on a long enameled part of equivalent diameter less than 100 mm ; and

   - said forging comprises at least two heating operations, the first to a temperature that is below or above the β transition, and the last to a temperature that is above the β transition; the reduction ratio on each heating operation being greater than or equal to 2, and the forging speed lying in the range 1 s^-1 to 1×10^-5 s^-1.
6. The method according to claim 5, characterized in that said forging comprises three heating operations: first and second operations that are independently above or below the β transition, and a third operation that is above the β transition.
7. The method according to claim 5 or 6, characterized in that it includes re-enameling the part between two heating operations.
8. The method according to any one of claims 5 to 7, characterized in that the forging die is maintained at a temperature lying in the range 100°C to 700°C.
9. The method according to any one of claims 5 to 8, characterized in that said quenching is implemented under conditions which induce a cooling speed that is less than or equal to the speed induced by quenching in a bath of oil.
10. The method according to any one of claims 5 to 9, characterized in that said tempering is implemented at a temperature lying in the range 620°C to 750°C for a period lying in the range 3 h to 5 h.
11. The method according to any one of claims 5 to 10, characterized in that:

    - said long enameled part is made of Ti₁₇ alloy (TA₅CD₄ or TiAl₅Cr₂MO₄);

    - said forging comprises a first heating operation at a temperature less than or equal to 840°C ± 10°C or at a temperature greater than or equal to 940°C ± 10°C, and a second heating operation at a temperature of 940°C ± 10°C;

    - said quenching is implemented on die and then in still air; and

    - said tempering is implemented at 630°C for 4 h.

Images