制备工艺对FGH4097高温合金微观组织与性能的影响

Effects of Processing on Microstructures and Properties ofFGH4097 Superalloy

利用SEM、EBSD和TEM等实验技术研究了放电等离子烧结(SPS)和热压(HP)法制备的FGH4097粉末高温合金的微观结构、力学性能和氧化行为。结果表明:SPS态合金具有组织均匀、晶粒细小、碳化物析出少等优点,具有更为优异的拉伸性能和抗高温氧化性能,其室温屈服强度和抗拉强度分别为998和1401 MPa,延伸率达17.1%。而HP态合金的室温屈服强度、抗拉强度和延伸率分别为951 MPa、1262 MPa和14.4%。在700℃下2种合金的屈服强度和抗拉强度相差不大,但SPS态的塑性比HP态提高约80%。2种合金在900℃下氧化100 h的氧化增重均遵循抛物线定律,但HP态的氧化速率约是SPS态的2.6倍,其主要原因是SPS态合金表面生成一层连续致密的Al2O3内膜,而HP态合金表面生成大量的非保护性的NiCr2O4和TiO2,内部也发生了严重的内氧化。

Powder metallurgy(PM)nickel-based superalloys are widely used as high-temperature,fatigue-resistant components in aircraft and gas turbines.However,many powder particle boundaries and carbides are found in alloys prepared via traditional methods,such as hot pressing(HP)and hot isostatic pressing,causing serious damage to the properties of PM superalloys.New methods and processes must be developed to improve the performance of PM superalloys.SEM,EBSD,and TEM were used in this work to investigate the microstructure,mechanical properties,and oxidation behavior of FGH4097 alloys prepared via spark plasma sintering(SPS)and HP.Owing to the advantages of uniform microstructure,fine grain,and less carbide precipitation,SPSed alloy has better tensile properties and oxidation resistance than HPed alloy.At 25℃,SPSed alloy􀆳s yield,tensile strengths,and elongation are 998 MPa,1401 MPa, and 17.1%, respectively;whereas those of HPed alloy are 951 MPa, 1262 MPa, and 14.4%,respectively. Although the two alloys exhibit similar yield and tensile strengths at 700℃, SPSed alloyshows merely 80% higher ductility than HPed alloy. The oxidation mass gain of the two alloys oxidized at900℃ for 100 h follows the parabolic law. A continuous and dense Al_(2)O_(3) scale is formed on the surface ofSPSed alloy, which effectively prevents the inward diffusion of O and outward diffusion of Cr and Ti. Themass gain is merely 0.19 mg/cm^(2), and the oxidation rate is 1.03 × 10^(-7) mg^(2)/(cm^(4)·s). Conversely, the oxidationrate of HPed alloy is approximately 2.6 times that of SPSed alloy. Severe internal oxidation occurs inHPed alloy, resulting in abundant less protective NiCr_(2)O_(4) and TiO2 formation on the surface, as well aslarge cracks and spalling.