Titanium alloy heat treatment process, and part thus obtained

Abstract

Ti 5-5-5-3 titanium alloy heat treatment process having, in weighted percentages, the following composition: between 4.4 and 5.7% aluminum, between 4.0 and 5.5% vanadium, between 0.30 and 0.50% iron, between 4.0 and 5.5% molybdenum, between 2.5 and 3.5% chromium, between 0.08 and 0.18% oxygen, 0.10% traces of carbon, 0.05% traces of nitrogen, 0.30% traces of zirconium, 0.15% traces of silicon, the residual percentage being titanium and impurities, characterised in that the heat treatment of said alloy is carried out by: heating to a first stage of between 810 and 840′° C. and below the β-transus temperature of the alloy; maintaining at the first stage for one to three hours; cooling to a second stage of between 760° C. and 800° C. without intermediate reheating; maintaining at the second stage for two to five hours; cooling to ambient temperature; heating to a third stage of between 540° C. and 650° C.; maintaining at the third stage for four to twenty hours, then cooling to ambient temperature. Part obtained by this process.

1 . Ti 5-5-5-3 titanium alloy heat treatment process having, in weighted percentages, the following composition:
 between 4.4 and 5.7% aluminum,   between 4.0 and 5.5% vanadium,   between 0.30 and 0.50% iron,   between 4.0 and 5.5% molybdenum,   between 2.5 and 3.5% chromium,   0.08 to 0.18% oxygen,   0.10% traces of carbon,   0.05% traces of nitrogen,   0.30% traces of zirconium,   0.15% traces of silicon,   
     the residual percentage being titanium and impurities resulting from production, characterised in that a heat treatment of said alloy is carried out, comprising a plurality of steps and heat stages distributed in the following way:
 the titanium alloy is heated to a first heat stage temperature of between 810 and 840° C., lower than the β-transus temperature of the alloy; 
 the titanium alloy is maintained at the first stage temperature for one to three hours; 
 the titanium alloy is cooled to a second stage temperature of between 760° C. and 800° C. without intermediate reheating; 
 the titanium alloy is maintained at the second stage temperature for two to five hours; 
 the titanium alloy is cooled to ambient temperature; 
 the titanium alloy is heated to a third stage temperature of between 540° C. and 650° C.; 
 the titanium alloy is maintained at the third stage temperature for four to twenty hours, then cooled to ambient temperature. 
 
   
   
       2 . Process according to  claim 1 , characterised in that the temperatures and durations of the first and second stages are determined to obtain an alpha phase quantity of between 2 and 5% at the end of the first stage and a globular primary alpha phase quantity of between 10 and 15% at the end of the second stage. 
   
   
       3 . Process according to  claim 1 , characterised in that the first stage is carried out at a temperature between the β-transus temperature less 20° C. and the β-transus temperature less 30° C., and in that the second stage is carried out at a temperature of between 770° C. and 790° C. 
   
   
       4 . Process according to  claim 1  characterised in that the first and second stages are carried out successively. 
   
   
       5 . Process according to  claim 1 , characterised in that the cooling speed between the first stage and the second stage is between 1.5° C. and 5° C. per minute and cooling at the end of the second stage is carried out to ambient temperature at a speed of between 5° C. and 150° C. per minute. 
   
   
       6 . Process according to  claim 1 , characterised in that the titanium alloy is maintained at the third stage temperature for six to ten hours, preferably for about eight hours. 
   
   
       7 . Part made of Ti 5-5-5-3 alloy, characterised in that it has been obtained from a half-finished product obtained by the heat treatment process according to  claim 1 .