Investigation Of Microstructure And Mechanical Properties And Purification Technology Of Nickel-based Superalloy

The GH4169 and K418 superalloy rods with different diameters(6、8、 10mm) are prepared by vacuum suction casting method in water cooling copper crucible, then the following main aspects have been investigated.Influence of cooling rate on microstructure and mechanical properties of GH4169 were investigated by XRD, SEM and EDS. The results show that with the increase of cooling rate, the dendrite microstructure becomes refined, the secondary dendrite arm spacing decreases, Laves phase size is reduced and distributed dispersedly, segregation of Nb and Mo elements is mitigated, the strength and hardness of the alloy increases, elongation decreases. Compared to the cast microstructure, alloys after heat treatment precipitate y’phase, Laves phase present blocky and small, and distribute more dispersedly, toothed grain boundaries appear. Moreover, with the increase of cooling rate, precipitated phase size still becomes small.Influence of cooling rate on microstructure and mechanical properties of K418 were investigated. Research indicates that K418 cast alloy presented dendritic morphology, dendrite is developed with a certain direction. With the increase of cooling rate, the secondary dendrite arm spacing decreases, γ’strengthening phase size becomes small gradually and its shape shows regular cube, rockwell hardness and tensile strength increases, elongation decreases; Compared to the cast microstructure, after heat treatment, the number of y’phase reduces, the size of γ’phase increases, the morphology of y’phase becomes irregular. So the alloy mechanical properties get worse than cast alloy.The effects of heat treatment on K418 alloy microstructure and mechanical properties were investigated by changing the solution cooling ways and solution holding time. The results show that with the increase of solution cooling rate, γ’phase becomes more and smaller, the shape gets irregular. In contrast, the cooling rate is smaller, the γ’phase precipitated is larger. In addition, rapid cooling rate can make carbides refined, hardness and tensile strength of the alloy by water cooling is the best. With the extension of the solution time, γ’phase size increases slightly, tends to be cube. Among them, γ’phase of solution for 3h is the best, at the same time, the strength and hardness are the highest.The effects of different composite molten salt scavengers on GH4169 return alloy were investigated. Results show that O, N, C, S content in original alloy is higher, but after purification of different scavengers, their content have declined substantially. Alloy oxygen content and nitrogen content decreases significantly after being purified by the following scavenger, that is 50% CaF2+45% AlF3+5% CaO+microscale (Al2O3+MgO).