Effect of preheating treatment on FGH4108 superalloy powder

FGH4108 is a newly designed fourth generation powder metallurgy superalloy. In this paper, the microstructure, precipitate and element distribution of FGH4108 powder prepared by argon atomization after preheating treatment at different temperatures were characterized and analyzed. The effect of preheating temperature on the carbide evolution and surface state of FGH4108 powder was systematically studied. The results show that the carbide forming elements (Ta, Nb, Ti, Hf, Cr, W, Mo) and C of the powder are enriched towards the interior during preheating treatment. As preheating temperature increases, the degree of elemental enrichment increases, the oxidation degree of the powder surface and the oxygen content in the precipitated phase increase. The metastable MC' carbides in the powder transform into stable MC carbides, and the contents of Ta, Nb, Ti and Hf in the carbides increase with the increase of preheating temperature. At the same time, M₂₃C₆ and M₆C carbides are formed. When preheating temperature is less than 1050 °C, the two coexist, and M₂₃C₆ carbides are not observed after 1100 °C. In addition, γ′ phase is also precipitated in the powder. As preheating temperature increases, the morphology changes from round to square and the size increases. The increase of preheating temperature promotes the homogenization of the powder microstructure, and precipitates changes from continuous intergranular distribution to dispersed distribution. More C elements are fixed in carbides by strong carbide forming elements. This improves the stability and distribution of carbides in the powder, which is beneficial to reduce the continuous precipitation of carbides on the surface of the powder during hot isostatic pressing.