EP1340832A1 - Thin products made of beta or quasi beta titanium alloys, manufacture by forging - Google Patents

Abstract

Non-axisymetric manufactured products, with a thickness less than 10 mm are made of beta or quasi beta titanium alloys and have a core microstructure made up of whole grains with a leanness ratio greater than 4 and an equivalent diameter of between 10 and 300 microns. These products are made by forging and from titanium alloys of the Ti17 (TA5CD4 or TiAl5Cr2MO4) type. An Independent claim is also included for the fabrication of these products by forging.

Description

The present invention relates to thin products in titanium alloys β or quasi β 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.

More specifically, it concerns:

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

The context of conception and development of the invention currently claimed was that of disc manufacturing monobloc blades (DAM) with blades added by friction welding linear. Said monoblock bladed discs, with reference to their mechanical properties and in particular their resistance to fatigue vibratory, are generally made of a titanium alloy β or quasi β. They are obtained, to date, by machining, in a solid crude.

Unlike obtaining such blades by forging discs made of a β or quasi β titanium alloy, there was a real prejudice. The forging of structures in β or quasi β titanium alloys, i.e. coarse-grained structures, to produce thin parts (blades), a priori could only lead to such parts, with properties mechanical (notably impact resistance, fatigue resistance disappointing.

Surprisingly, in the context of this invention, blades (thin products) made of β or quasi β titanium alloys efficient (with good metallurgical health and good mechanical characteristics) were obtained by forging (i.e. with material saving, compared to the machining technique, conventionally implemented). Said blades also have durations of life superior to that of blades obtained by machining; they can also be obtained with optimized geometries, allowing improve aerodynamics, therefore engine performance in which they are likely to intervene.

The invention was therefore conceived and developed, in a manner not obvious, in this context of bladed disc manufacturing monoblocks (DAM). However, it is by no means limited to said context; it is also expressed quite naturally in more or less less closely related, such as the manufacture of one-piece bladed rings (ANAM), those for the repair of said monoblock bladed discs (DAM) and monoblock bladed rings (ANAM), and more generally that of the manufacture of β or quasi β titanium thin products.

Control of the forging, according to the invention, of pieces of alloys β or quasi β titanium, of small thicknesses, made it possible to obtain thin products, in said titanium alloys β or quasi β, original by their microstructure at heart.

The said products constitute the first object of this invention.

The controlled forging process which leads to said products in is the second object.

According to its first object, the present invention therefore relates to manufactured, non-axisymmetric products (wires are thus excluded), less than 10 mm thick (these 10 mm specify the concepts of "thin", "thin products", used in this text), made of β or quasi β titanium alloys, the microstructure of which is made up of whole grains with a slenderness rate higher than 4 and an equivalent diameter between 10 and 300 µm.

Titanium alloys β or quasi β (which can also be qualified closely related β) are familiar to those skilled in the art. They present a compact hexagonal structure. They are perfectly defined, in particular in American Handbooks (US): ASMH (AMERICAN SOCIETY MATERIAL HANDBOOK) and MILH (MILITARY HANDBOOK). Their use is, to date, confined to the manufacture of forgings massive or very thick.

Typically, manufactured products from the invention, in said alloys, are thin products which bear 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 rate greater than 4; said rate of slenderness being conventionally defined as the ratio of the most large dimension on the smallest dimension in the cutting plane axial.

They have an equivalent diameter between 10 and 300 µm.

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

The manufactured products of the invention, by the characteristics set out above, are new products. These new products are likely to be obtained by forging. As explained previously, there was a real bias to seek thin structures by forging thicker to coarse structures grains and, surprisingly enough, such thin structures have been shown to have very interesting features.

The manufactured products of the invention consist advantageously in the blades of turbomachine compressors.

The invention is however not limited to this context. The products involved may also consist of propellers, submarines in particular, in blades of fans or mixers (likely to intervene in circles justifying the constitution said blades made of β or quasi β titanium alloys). This list cannot be exhaustive.

According to a particularly preferred variant (in no way limiting), the manufactured products of the invention are made of Ti ₁₇ alloy. This alloy, familiar to those skilled in the art, is used today to manufacture massive parts, in particular compressor disks. It has high flow constraints and also has the reputation of being difficult to forge.

TA₅CD₄, selon la nomenclature métallurgique,

TiAl₅Cr₂MO₄, selon la nomenclature chimique.

It is more precisely about the alloy:

TA ₅ CD ₄ , according to the metallurgical nomenclature,

TiAl ₅ Cr ₂ MO ₄ , according to the chemical nomenclature.

Quite surprisingly, the inventors have, in the context of the presently claimed invention, forged thin parts, in said Ti ₁₇ alloy, with high degree of wrought; said forgings having high mechanical properties.

We now come to the second object of this invention, namely the process for manufacturing new products, described above.

• l'obtention d'un lopin émaillé ;
• la transformation, si nécessaire, dudit lopin en un produit long d'un diamètre équivalent inférieur à 100 mm ;
• le forgeage dudit produit long ;
• la trempe dudit produit long forgé ; et
• le revenu dudit produit long forgé trempé.

Said manufacturing process comprises:

• obtaining an enameled piece;
• transforming, if necessary, said piece into a long product with an equivalent diameter of less than 100 mm;
• forging said long product;
• quenching said long forged product; and
• the income of said long tempered forged product.

The product to be forged is, conventionally, previously enamelled.

Said product generally consists of a semi-finished product, obtained by spinning or forging a starting material with a larger diameter equivalent (thicker). It can in particular be a bar (having, for example, a diameter of 25 mm), obtained by spinning a billet. Titanium alloys β or close β indeed exist mainly in the form of such billets (intended for the manufacture compression discs by machining).

This enameled product, generally therefore semi-enameled product, with a diameter (equivalent) of less than 100 mm, is, according to the invention, transformed by forging into a thick manufactured product 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, the implementation of forging is recommended under the conditions below. The forging operation includes at least two hot ones:

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

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

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

The forging operation can absolutely be limited to both hot, as specified above (the second of said two hot being imperatively a hot in super transus β). It can include an additional hot, in sub or super β transus, before the last (third) hot in super β transus. It is not totally excluded that it includes more than three hot ones (the last of these hot ones being imperative a hot in super transus β) but the advantage of multiplying thus the number of hot is not obvious.

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

Conventionally, the forged product is possibly re-enamelled between two successive warms.

According to an advantageous variant of implementation, the matrix is kept at a temperature between 100 and 700 ° C.

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

The income of the forged, quenched product is advantageously put used at a temperature between 620 and 750 ° C, for 3 to 5 a.m. We optimize its conditions of implementation according to characteristics sought for the finished product. We take care to perform said returned under an inert atmosphere (especially vacuum or argon) if the enameling is cracked or chipped.

• le lopin 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 method of the invention is implemented under the conditions below:

• the piece is made of Ti ₁₇ alloy (TA ₅ CD ₄ or TiAl ₅ Cr ₂ MO ₄ );
• forging includes 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 (in super transus β) and a second hot at a temperature 940 ± 10 ° C (in β super transus);
• quenching is carried out on a matrix then in calm air;
• the tempering is carried out at 630 ° C for 4 h.

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

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

In Figures 1 and 2 attached, we show, at different scales, the core microstructure - original microstructure - of such dawn.

In Figure 1 - section in three directions: section transverse according to plane A, longitudinal according to plane B and facial according to plan C; magnification: x 20 - we can clearly see the lenticular shape grains: strongly crushed in the transverse and longitudinal and with a broad face in the facial section.

In Figure 2 - high magnification: x 5000 - we show the internal grain microstructure. We referenced 1 a hardened grain, 2 a recrystallized grain. The α needles are very fine and very tangled.

Example : Manufacture of a Ti ₁₇ blade by forging.

• filage d'une barre ( < 100 mm) pour obtenir un lopin ( : 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.
• 2ême 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 implemented comprises the following successive steps:

• spinning a bar ( <100 mm) to obtain a piece (: 27 mm) 240 mm long;
• enameling;
• radial crushing of the extruded bar to form the blade and the base;
• forging die brought to 200 ° C;
• typing speed (screw press): 10 ^-4 s ^-1 ;
• 1 ^st hot: the enameled piece, maintained for 45 min at 940 ° C (hot in super transus β) is crushed until it has a thickness of 13 to 8 mm.
• 2nd hot: Conditions identical to the 1 ^st New crushing generates a piece whose thickness ranges from 9 to 1 mm.
• cooling on matrix then by calm air on table;
• direct tempering after forging at 630 ° C / 4 h.

It generates a dawn whose microstructure at heart is such that shown in the accompanying figures.

Claims (12)

Manufactured products, not axisymmetric, of a thickness less than 10 mm, in β or quasi β titanium alloys, the microstructure at heart consists of whole grains with a rate slenderness greater than 4 and an equivalent diameter between 10 and 300 µm. Manufactured products according to claim 1, susceptible to be obtained by forging. Manufactured products according to either of Claims 1 or 2, consisting of turbine engine compressor blades. Manufactured products according to any one of claims 1 to 3, in Ti ₁₇ alloy (TA ₅ CD ₄ or TiAl ₅ Cr ₂ MO ₄ ). Method of manufacturing a product according to any one of the preceding claims, characterized in that it comprises: obtaining an enameled piece; transforming, if necessary, said piece into a long product with an equivalent diameter of less than 100 mm; forging said long product; quenching said long forged product; and the income of said long tempered forged product. A method according to claim 5, characterized in that said forging comprises at least two hot ones, the first in sub or super transus β and the last in super transus β; the reduction rate at each heat being greater than or equal to 2 and the forging speeds being between 1 and 1.10 ^-5 s ^-1 . A method according to claim 6, characterized in that said forging comprises three hot; a first and a second, independently, in sub or super transus β and a third in super transus β. Method according to one of claims 6 or 7, characterized in that it comprises a re-enamelling of the product between two heaters. Process according to any one of Claims 5 to 8, characterized in that the forging matrix is maintained at a temperature between 100 and 700 ° C. Process according to any one of Claims 5 to 9, characterized in that the said quenching is carried out under conditions which induce a cooling rate less than or equal to that induced by quenching in an oil bath. Process according to any one of Claims 5 to 10, characterized in that the said tempering is carried out at a temperature between 620 and 750 ° C, for 3 to 5 h. Method according to any one of Claims 5 to 11, characterized in that : said piece is of Ti ₁₇ alloy (TA ₅ CD ₄ or TiAl ₅ Cr ₂ MO ₄ ); said forging comprises a first hot at a temperature less than or equal to 840 ± 10 ° C or at a temperature greater than or equal to 940 ± 10 ° C and a second hot at a temperature of 940 ± 10 ° C; said quenching is carried out on a matrix then in calm air; and said tempering is carried out at 630 ° C for 4 hours.

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