METHOD OF FORMING PRECURSOR INTO A TI ALLOY ARTICLE

Abstract

A method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, is described. The method comprises: providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate, comprising, substantially comprising, essentially comprising and/or consisting of an α+β Ti alloy having a beta transus temperature β.sub.transus, wherein the precursor defines a set of portions including a first portion; and thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε.sub.1, total, wherein the total true strain ε.sub.1, total is greater than a predetermined threshold true strain ε.sub.threshold; wherein thermomechanically forming the article from the precursor comprises i iterations of: (a) heating the first portion to a temperature T.sub.i during a time t.sub.i wherein the temperature T.sub.i is at most the beta transus temperature β.sub.transus; (b) deforming the heated first portion by a true strain ε.sub.1,i, wherein the true strain ε.sub.1,i is at most the predetermined threshold true strain ε.sub.threshold and (c) repeating steps (a) and (b) until the cumulative true strain ε.sub.1,cumulative=Σ.sub.iε1,ieu is the total true strain ε.sub.1, total wherein i is a natural number greater than or equal to 2.

Claims

1. A method of thermomechanically forming, an article from a precursor thereof, the method comprising: providing the precursor, comprising an α+β Ti alloy having a beta transus temperature β.sub.transus, wherein the precursor defines a set of portions including a first portion; and thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε.sub.1,total, wherein the total true strain ε.sub.1,total is greater than a predetermined threshold true strain ε.sub.threshold, wherein thermomechanically forming the article from the precursor comprises i iterations of: (a) heating the first portion to a temperature T.sub.i during a time t.sub.i, wherein the temperature T.sub.i is at most the beta transus temperature β.sub.transus; (b) deforming the heated first portion by a true strain ε.sub.1,i, wherein the true strain ε.sub.1,i is at most the predetermined threshold true strain ε.sub.threshold; and (c) repeating steps (a) and (b) until the cumulative true strain ε.sub.1,cumulative=Σ.sub.iiε.sub.1,i is the total true strain ε.sub.1,total, wherein i is a natural number greater than or equal to 2, wherein the temperature T.sub.i is in a range from β.sub.transus−97° C. to β.sub.transus−3° C., wherein the time t.sub.i is in a range from 0.5 hours to 12 hours wherein i is equal to 1, wherein the time t.sub.i is in a range from 0.25 hours to 4 hours wherein i is greater than or equal to 2, and wherein the predetermined threshold true strain ε.sub.threshold is in a range from 0.5 to 0.85.

2. The method according to claim 1, wherein the predetermined threshold true strain ε.sub.threshold is in a range from 0.7 to 0.8.

3. The method according to claim 1, wherein deforming the heated first portion by the total true strain ε.sub.1,total comprises elongating the heated first portion by a total elongation (δL/L).sub.total, and wherein the total elongation (δL/L).sub.total is at least a predetermined threshold elongation (δL/L).sub.threshold.

4. The method according to claim 3, wherein the predetermined threshold elongation (δL/L).sub.threshold is in a range from 0.75 to 1.25.

5. The method according to claim 1, wherein providing the precursor comprises providing the precursor having a cross-sectional aspect ratio in a range from 3:4 to 4:3, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and/or providing the precursor having a longitudinal aspect ratio in a range from 50:1 to 3:2.

6. The method according to claim 1, wherein the temperature T.sub.i is in a range from β.sub.transus−69° C. to β.sub.transus−14° C.

7. The method according to claim 1, wherein the time t.sub.i in a range from 2 hours to 6 hours, and wherein i is equal to 1.

8. The method according to claim 1, wherein the time t.sub.i is in a range from 0.75 hours to 1.5 hours, and wherein i is greater than or equal to 2.

9. The method according to claim 1, further comprising β annealing the article at a temperature T.sub.β anneal during a time t.sub.β anneal, wherein the temperature T.sub.β anneal is at least the beta transus temperature β.sub.transus .

10. The method according to claim 1, further comprising stabilization annealing the article at a temperature T.sub.stabilization anneal during a time t.sub.stabilization anneal, wherein the temperature T.sub.stabilization anneal is less than the beta transus temperature β.sub.transus.

11. The method according to claim 1, wherein providing the precursor comprises vacuum arc melting, plasma arc melting and/or electron beam melting and/or vacuum arc re-melting the α+β Ti alloy.

12. A method of manufacturing a component comprising: thermomechanically forming an article according to claim 1; and machining the first portion of the article, thereby providing, at least in part, the component.

13. The method according to claim 12, comprising non-destructive testing of the machined component.

14. The method according to claim 12, wherein machining comprises removing an amount of the first portion in a range from 50% to 97.5% by volume of the first portion.

15. The method according to claim 1, wherein the α+β Ti alloy is AMS 6932 (AMS 6932, AMS 6932 Rev. A-C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A-F or later).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0126] For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

[0127] FIG. 1 schematically depicts a continuous cooling transformation (CCT) curve for a Ti-6Al-4V α+β Ti alloy;

[0128] FIG. 2 shows an optical micrography of a lamellar microstructure of a Ti-6Al-4V α+β Ti alloy;

[0129] FIG. 3 schematically depicts a method of thermomechanically forming an α+β Ti alloy;

[0130] FIG. 4 is a CAD drawing of an article according to an exemplary embodiment; and

[0131] FIG. 5 schematically depicts an exemplary method of thermomechanically forming the article of FIG. 4.

DETAILED DESCRIPTION

[0132] FIG. 3 schematically depicts a method of thermomechanically forming an α+β Ti alloy. It should be understood that the exemplary method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof relates to at least the step of pre-form forging and optionally, to the steps of die forging and/or subsequent heat treatment.

[0133] FIG. 4 is a CAD drawing of an article 10, particularly for machining into a rib for an aircraft (i.e. an aerospace component), according to an exemplary embodiment.

[0134] The article 10 was thermomechanically formed according to an exemplary embodiment, as described with respect to FIG. 5, from a precursor 1 wherein the precursor 1 is a forging stock particularly a square bar, having a width of 6″ (152 mm), a height of 6″ (152 mm) and a length of 47″ (1194 mm). The article 10 has a length of about 96″ (2438 mm).

[0135] FIG. 5 schematically depicts an exemplary method of thermomechanically forming the article 10 of FIG. 4.

[0136] In more detail, FIG. 5 compares a conventional method of thermomechanically forming a conventional article (labelled ‘Current Process’) and the exemplary method of thermomechanically forming the exemplary article 10 (labelled ‘New Process’).

[0137] The conventional method comprises:

[0138] providing a precursor, consisting of the α+β Ti alloy having a beta transus temperature β.sub.transus, wherein the precursor defines the set of 12 portions (labelled ‘Position 1 to 12’) including a first portion (labelled ‘Position 1’); and

[0139] thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by the total true strain ε.sub.1,total=1.39;

[0140] wherein thermomechanically forming the article from the precursor comprises 2 iterations of:

[0141] (a) heating the first portion to the temperature T.sub.i during the time t.sub.i, wherein the temperature T.sub.i is at most the beta transus temperature β.sub.transus;

[0142] (b) deforming the heated first portion 100A by a true strain ε.sub.1,i, wherein the true strain ε.sub.1,i, is the total true strain ε.sub.1,total=1.39;

[0143] β annealing the thermomechanically formed article 10 at a temperature T.sub.β anneal during a time t.sub.βanneal, wherein the temperature T.sub.B anneal is at least the beta transus temperature β.sub.transus; and

[0144] stabilization annealing the (βannealed) article 10 at a temperature T.sub.stabilization anneal during a time t.sub.stabilization anneal, wherein the temperature T.sub.stabilization anneal is less than the beta transus temperature β.sub.transus;

[0145] wherein the α+β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A-C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A-F or later) and/or an equivalent and/or a variant thereof;

[0146] wherein deforming the heated first portion 100A by the total true strain ε.sub.1,total comprises elongating the heated first portion 100A by a total elongation (δL/L).sub.total, wherein the total elongation (δL/L).sub.total is at least a predetermined threshold elongation (δL/L).sub.threshold;

[0147] wherein the predetermined threshold elongation (δL/L).sub.threshold is about 1″(25.4mm);

[0148] wherein providing the precursor 1 comprises providing the precursor 1 having a cross-sectional aspect ratio of 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and providing the precursor 1 having a longitudinal aspect ratio of about 8:1;

[0149] wherein the temperature T.sub.i is in a range from β.sub.transus−125° F. (69° C.) to β.sub.transus−25° F. (1.4° C.);

[0150] wherein the time t.sub.i is about 3 hours wherein i is equal to 1.

[0151] In this particular example according to the conventional method, the precursor is a forging stock particularly a square bar, having a width of 6″ (152 mm), a height of 6″ (152 mm) and a length of 47″ (1194 mm), while the length of the article is about 96″ (2438 mm).

[0152] In the conventional method, ‘Positions 1 to 12’ are deformed during the 1st iteration (i.e. wherein i is equal to 1) while only ‘Positions 8 to 12’ are deformed during the 2nd iteration (i.e. wherein i is equal to 2).

[0153] In the 1st iteration (i.e. wherein i is equal to 1), the heated first portion ‘Position 1’ is deformed by a true strain ε.sub.1,1=1.39 and the heated eleventh portion ‘Position 11’ is deformed by a true strain ε.sub.11,1 =0.17, by way of example.

[0154] In the 2nd iteration (i.e. wherein i is equal to 2), the heated first portion ‘Position 1’ is deformed by a true strain ε.sub.1,2=0 and the heated eleventh portion ‘Position 11’ is deformed by a true strain ε.sub.1,2=1.30.

[0155] The exemplary method is of thermomechanically forming by forging the article 10 from the precursor 1 (not shown) thereof, the method comprising:

[0156] providing the precursor 1, consisting of the α+β Ti alloy having a beta transus temperature β.sub.transus, wherein the precursor 1 defines the set of 12 portions 100 (labelled ‘Position 1 to 12’) including a first portion 100A (labelled ‘Position 1’); and

[0157] thermomechanically forming the article 10 from the precursor 1 by heating the first portion 100A and deforming the heated first portion 100A by the total true strain ε.sub.1,total, wherein the total true strain ε.sub.1,total is greater than the predetermined threshold true strain ε.sub.threshold;

[0158] wherein thermomechanically forming the article 10 from the precursor 1 comprises 2 iterations of:

[0159] (a) heating the first portion 100A to the temperature T.sub.i during the time t.sub.i, wherein the temperature T.sub.i is at most the beta transus temperature β.sub.transus;

[0160] (b) deforming the heated first portion 100A by a true strain ε.sub.1,i, wherein the true strain ε.sub.1,i, is at most the predetermined threshold true strain ε.sub.threshold;

[0161] (c) repeating steps (a) and (b) until the cumulative true strain ε.sub.1,cumulative=Σ.sub.iε.sub.1,i is the total true strain ε.sub.1,total, wherein i is 4;

[0162] thermomechanical processing the thermomechanically formed article 10, for example block and finish forging of the thermomechanically formed article 10;

[0163] ⊖ annealing the thermomechanically formed article 10 at a temperature T.sub.β anneal during a time t.sub.β anneal, wherein the temperature T.sub.β anneal is at least the beta transus temperature β.sub.transus; and

[0164] stabilization annealing the (β annealed) article 10 at a temperature T.sub.stabilization anneal during a time t.sub.stabilization anneal, wherein the temperature T.sub.stabilization anneal is less than the beta transus temperature β.sub.transus;

[0165] wherein the α+β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A-C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A-F or later) and/or an equivalent and/or a variant thereof;

[0166] wherein the predetermined threshold true strain ε.sub.threshold is 0.75 (i.e. 75%);

[0167] wherein deforming the heated first portion 100A by the total true strain ε.sub.1,total comprises elongating the heated first portion 100A by a total elongation (δL/L).sub.total, wherein the total elongation (δL/L).sub.total is at least a predetermined threshold elongation (δL/L).sub.threshold;

[0168] wherein the predetermined threshold elongation (δL/L).sub.threshold is about 1″ (25.4 mm);

[0169] wherein providing the precursor 1 comprises providing the precursor 1 having a cross-sectional aspect ratio of 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and providing the precursor 1 having a longitudinal aspect ratio of about 8:1;

[0170] wherein the temperature T.sub.i is in a range from β.sub.transus−125° F. (69° C.) to β.sub.transus−25° F. (14° C.);

[0171] wherein the time t.sub.i is about 3 hours wherein i is equal to 1;

[0172] wherein the time t.sub.i is about 1 hour, wherein i is greater than or equal to 2; and

[0173] wherein a maximum prior β grain size of the α+β Ti alloy in the first portion 100A of the article 10 is in a range from 10 μm to 25 mm, preferably in a range from 100 μm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.

[0174] In this particular example according to the exemplary method, the precursor 1 is a forging stock particularly a square bar, having a width of 6″ (152 mm), a height of 6″ (152 mm) and a length of 47″ (1194 mm), while the length of the article 10 is about 96″ (2438 mm).

[0175] In the exemplary method, ‘Positions 1 to 12’ are deformed during the 1st iteration (i.e. wherein i is equal to 1), ‘Positions 1, 2 and 4’ are deformed during the 2nd iteration (i.e. wherein i is equal to 2), ‘Positions 8 to 12’ are deformed during the 3rd iteration (i.e. wherein i is equal to 3) and ‘Positions 8 and 11’ are deformed during the 4th iteration (i.e. wherein i is equal to 4).

[0176] Particularly, in the 1st iteration (i.e. wherein i is equal to 1), the heated first portion 100A (Position 1) is deformed by a true strain ε.sub.1,1=0.75, wherein the true strain ε.sub.1,1 is at most the predetermined threshold true strain ε.sub.threshold, and the heated eleventh portion 100K (Position 11′) is deformed by a true strain ε.sub.11,1=0.17, wherein the true strain ε.sub.11,1 is at most the predetermined threshold true strain ε.sub.threshold, wherein the predetermined threshold true strain ε.sub.threshold is 0.75 (i.e. 75%).

[0177] Particularly, in the 2nd iteration (i.e. wherein i is equal to 2), the heated first portion 100A (Position 1′) is deformed by a true strain ε.sub.1,2=0.64, wherein the true strain ε.sub.1,2 is at most the predetermined threshold true strain ε.sub.threshold, and the heated eleventh portion 100K (Position 11′) is deformed by a true strain ε.sub.11,2=0, wherein the true strain ε.sub.11,2 is at most the predetermined threshold true strain ε.sub.threshold, wherein the predetermined threshold true strain ε.sub.threshold is 0.75 (i.e. 75%).

[0178] Particularly, in the 3rd iteration (i.e. wherein i is equal to 3), the heated first portion 100A (Position 1′) is deformed by a true strain ε.sub.1,3=0, wherein the true strain ε.sub.1,3 is at most the predetermined threshold true strain ε.sub.threshold, and the heated eleventh portion 100K (Position 11′) is deformed by a true strain ε.sub.11,3=0.58, wherein the true strain ε.sub.11,3 is at most the predetermined threshold true strain ε.sub.threshold, wherein the predetermined threshold true strain ε.sub.threshold is 0.75 (i.e. 75%).

[0179] Particularly, in the 4th iteration (i.e. wherein i is equal to 4), the heated first portion 100A (Position 1′) is deformed by a true strain ε.sub.1,4=0, wherein the true strain ε.sub.1,4 is at most the predetermined threshold true strain ε.sub.threshold, and the heated eleventh portion 100K (Position 11′) is deformed by a true strain ε.sub.11,4=0.72, wherein the true strain ε.sub.11,4 is at most the predetermined threshold true strain ε.sub.threshold, wherein the predetermined threshold true strain ε.sub.threshold is 0.75 (i.e. 75%).

[0180] That is, compared with the conventional method, the number of heating steps has been increased from 2 to 4 while the respective portions are deformed by at most the predetermined threshold true strain ε.sub.threshold of 0.75 (i.e. 75%).

[0181] While the yield for the conventional process was about 80%, due to disposal of components having relatively coarse prior β grain size, the yield for the exemplary process was improved to approaching 100%.

[0182] Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

[0183] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0184] All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or o process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

[0185] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, is equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0186] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.