Effects of Two-Step Sub-solution Heat Treatment on Microstructure of New As-Forged Nickel-Based Powder Superalloy Turbine Disc
The effect of two-step sub-solution heat treatment process on the γ'phase microstructure of a novel nickel-based powder metallurgy superalloy FGH4113A(WZ-A3)was studied.The results show that the cooling rate of large-size forged turbine disc is lower after forging,and the size distribution of γ'phases is from about 100 nm to 4500 nm.Small samples were taken from the disc for heat treatment experiments.When the samples are heated to 1000 and 1050 ℃,the total proportion of γ'phases decreases,and the evolution mechanism shows signs of Oswald coarsening mechanism and PAM mechanism.When the sample is heated to 1100 ℃,the intracrystalline γ'phase is completely dissolved.If two-step sub-solution heat treatment process is used,the sample is first heated to 1120 ℃ for 2 h followed by rapid cooling,and then heated to 1000,1050 or 1100 ℃.The total proportion of γ'phases decreases.The evolution of intracrystalline γ'phases is dominated by the Oswald coarsening mechanism,and its morphology and size are relatively stable during the heating process.The testing rods were cut from the disc and went through experiments:as-forged state+1000 ℃(without heat preservation)+aging heat treatment and as forged state+1120 ℃/2 h+aging heat treatment.The tensile tests were conducted at 550 ℃.The yield and tensile strengths of the latter one are significantly higher than those of the first one,and this can be treated as a reference for dual-performance heat treatment process design of large-size turbine discs.
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