Method of preparing a metal alloy part

Abstract

A method of converting an alloy comprising a majority of titanium, the method comprising: a step of fabricating an ingot ( 1 ); steps of a first type (A, B, C) of plastically deforming the alloy at a temperature higher than the β transus temperature Tβ; steps of a second type (A′, B′) of plastically deforming the alloy at a temperature lower than the β transus temperature Tβ. These step of the first and second types (A, A′, B, B′, C) are performed in the following sequence: a first step of the first type (A) at a first temperature T 1; a first step of the second type (A′); a second step of the first type (B) at a second temperature T 2 lower than T 1; a second step of the second type (B′); and a third step of the first type (C) at a third temperature T 3 lower than T 2.

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); 
 the method being characterized in that the steps of the first and second types (A, A′, B, B′, C) are applied in the following sequence: 
 performing the first step of the first type (A) while the alloy is at a first temperature (T 1 ); 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 (T 2 ) strictly lower than said first temperature (T 1 ); 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 (T 3 ) strictly lower than said second temperature (T 2 ). 
 
     
     
         2 . An alloy conversion method according to  claim 1 , wherein:
 the first temperature (T 1 ) is higher than the β transus temperature (Tβ) by at least 200° C. and at most 300° C.;   the second temperature (T 2 ) is higher than the β transus temperature (Tβ) by at least 100° C. and at most 200° C.;   the third temperature (T 3 ) 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  claim 1 , wherein 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. 
     
     
         4 . An alloy conversion method according to  claim 1 , 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. 
     
     
         5 . An alloy conversion method according to  claim 4 , 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. 
     
     
         6 . An alloy conversion method according to  claim 5 , wherein the deformation (R 1 ) 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). 
     
     
         7 . An alloy conversion method according to  claim 6 , wherein the deformation (R 3 ) 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). 
     
     
         8 . An alloy conversion method according to  claim 6 , wherein the deformation (R 5 ) 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). 
     
     
         9 . An alloy conversion method according to  claim 6 , wherein the deformation (E 2 ) 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′). 
     
     
         10 . An alloy conversion method according to  claim 9 , wherein the deformation (E 4 ) 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′). 
     
     
         11 . An alloy conversion method according to  claim 1 , wherein after the first step of the first type (C), a third step of the second type (C′) is performed. 
     
     
         12 . An alloy conversion method according to  claim 11 , 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. 
     
     
         13 . An alloy conversion method according to  claim 1 , wherein each of the steps of the second type is performed at a fourth temperature (T 4 ) 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. 
     
     
         14 . An alloy conversion method according to  claim 1 , 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. 
     
     
         15 . An alloy method according to  claim 1 , wherein the alloy is selected from the group of alloys comprising:
 a first alloy (Ti 10-2-3) comprising the following elements in percentages by weight:   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   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 
                   ≦0.013% 
                 
                     
                   titanium, Ti 
                     83%-86.8% 
                 
                     
                   vanadium, V 
                   9.0%-11%  
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
               
            
           
         
         a second alloy of type (Ti 5-5-5-3) comprising, the following elements in percentages by weight: 
       
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   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 alloy of type (Ti 5-5-5-3-1) comprising the following elements in percentages by weight: 
       
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   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 alloy of type (Ti 18) comprising the following elements, in percentages by weight: 
       
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   aluminum, Al 
                   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 balance being at least titanium and impurities; and
 a fifth alloy comprising the following elements, in percentages by weight: 
 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   titanium, Ti 
                   at least 84% 
                 
                     
                   aluminum, Al 
                   4%-7.5% 
                 
                     
                   oxygen, O 
                   at least 0.15% 
                 
                     
                   carbon, C 
                   at least 0.01% 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
               
            
           
         
         at least one element selected from vanadium, molybdenum, chromium, and iron, this fifth alloy also including hafnium and zirconium in addition at a percentage by weight of at least 0.1%. 
       
     
     
         16 . An aircraft landing gear, such as a landing gear rod, a strut, or a truck fabricated from an alloy converted in accordance with the alloy conversion method according to  claim 1 .