Nickel alloy

Abstract

A nickel-base alloy having the following composition (in weight percent unless otherwise stated): Cr 10.5-15.0; Co 1.7-8.8; Fe 0-5.9; Si 0-0.65; Mn 0-0.65; Mo 0.3-2.3; W 2.3-4.4; Al 2.7-4.1; Nb 1.0-4.2; Ti 1.0-3.0; Ta 2.0-5.0; Hf 0.0-0.6; C 0.02-0.06; B 0.015-0.035; Zr 0.035-0.11; S<20 ppm; P<60 ppm; the balance being Ni and incidental impurities. The alloy has an improved combination of properties (principally resistance to surface environmental damage and dwell fatigue crack growth) compared with known alloys, and is intended to operate for prolonged periods of time above 700° C., and up to peak temperatures of 800° C.

1 . A nickel-base alloy having the following composition (in weight percent unless otherwise stated): Cr 10.5-15.0; Co 1.7-8.8; Fe 0-5.9; Si 0-0.65; Mn 0-0.65; Mo 0.3-2.3; W 2.3-4.4; Al 2.7-4.1; Nb 1.0-4.2; Ti 1.0-3.0; Ta 2.0-5.0; Hf 0.0-0.6; C 0.02-0.06; B 0.015-0.035; Zr 0.035-0.11; S<20 ppm; P<60 ppm; the balance being Ni and incidental impurities. 
     
     
         2 . A nickel-base alloy having the following composition (in atomic percent unless otherwise stated): Cr 11.7-16.9; Co 1.7-8.75; Fe 0-6.2; Si 0-1.36; Mn 0-0.7; Mo 0.2-1.4; W 0.7-1.4; Al 5.8-8.8; Nb 0.63-2.65; Ti 1.2-3.7; Ta 0.6-1.6; Hf 0-0.2; C 0.1-0.29; B 0.08-0.19; Zr 0.022-0.071; S<20 ppm, P<60 ppm; the balance being Ni and incidental impurities. 
     
     
         3 . The alloy of  claim 2 , having the following composition (in atomic percent): Al 6.5-8.25; Ti 2.25-3.5; Nb 0.75-2.25; Ta 0.75-1.5; Si 0-1.2; and in which the sum of the atomic percentages of Al, Ti, Nb and Ta and 0.3 of the atomic percentage of Si is between 12.5 at. % and 13.5 at. %. 
     
     
         4 . The alloy of  claim 3 , in which the sum of the atomic percentages of Al, Ti, Nb and Ta and 0.3 of the atomic percentage of Si is 12.5 at. %. 
     
     
         5 . The alloy of  claim 3 , in which the sum of the atomic percentages of Al, Ti, Nb and Ta and 0.3 of the atomic percentage of Si is 13.5 at. %. 
     
     
         6 . The alloy of  claim 2 , having the following composition (in atomic percent): Al 7.0-7.5; Ti 1.5-2.0; Nb 2.0-2.5; Ta 1.0-1.5; Si 0-1.2; and in which the sum of the atomic percentages of Al, Ti, Nb and Ta and 0.3 of the atomic percentage of Si is 12.5 at. %. 
     
     
         7 . The alloy of  claim 2 , having the following composition (in atomic percent): Fe 0-5.5; Co 2.0-8.5; and in which the sum of the atomic percentages of Fe and Co is less than 8.5 at. %. 
     
     
         8 . The alloy of  claim 2 , having the following composition: S<5 ppm. 
     
     
         9 . The alloy of  claim 2 , having the following composition: P<20 ppm. 
     
     
         10 . A method of making a nickel-base alloy, the method comprising the steps of:
 a) producing a forging by a powder metallurgy technique, using powder having the composition of any one of the preceding claims;   b) solution heat treating the forging above the γ′ solvus temperature so as to grow the average grain size to ASTM 8 to 6 (22 to 45 μm) throughout, while preventing individual grains from growing to sizes greater than ASTM 2 (180 μm);   c) quenching the forging from the solution heat treatment temperature to room temperature by forced cooling or fan air cooling;   d) performing stabilisation/stress relief and precipitation heat treatments at a temperature between 800° C. and 870° C. for between 2 and 16 hours.   
     
     
         11 . The method of  claim 10 , in which step a) comprises the steps of:
 aa) consolidating small (<53 μm) powder particles from inert gas atomisation in a stainless steel container using hot isostatic pressing or hot compaction;   ab) using a hot working process to produce a fine grain size billet;   ac) cutting an increment from the billet and forging it under isothermal conditions.   
     
     
         12 . The method of  claim 10 , in which in step c) the cooling rate is defined so as to produce grain boundary serrations around secondary γ′ particles. 
     
     
         13 . The method of  claim 10 , in which the forging is in the form of a disc for a gas turbine engine, and further comprising the step of:
 e) performing a dual microstructure heat treatment on the forging to produce a fine (5 to 10 μm) average grain size in a bore and a diaphragm region of the disc.