Effect Of Melt Superheat Treatment On Microstructure And Mechanical Properties Of Nickel-Based Superalloy

The melt superheat treatment affects the microstructure of alloy, and then affects the mechanical properties of alloy. So, the effect of melt superheat treatment on microstructure and mechanical properties of K418,GH4169 and return material F418 alloy were investigated by the X ray diffraction, scanning electron microscopy(SEM) and electronic universal testing machine, etc.. The main results are as follows:After the melt superheat treatment of GH4169 alloy, the number of interdendritic Laves phase, eutectic γ+Laves and MC carbides are decreased and uniformly distributed; segregation degree of Nb and Mo element are significantly reduced; comprehensive mechanical properties is improve at room temperature. The tensile strength is about 1.5 times for a maximum of 721 Mpa compare with the before overheating treatment when the induction heating power is 3.7 KW. γ" and brittle δ phase are precipitate after heat treatment. δ phase is dissolved when the melt superheat temperature is high. Tensile strength and elongation increased by35.2% and 16.7% compare with the before heat treatment when the induction heating power is 4.5 KW, tensile strength has a maximum 1079 Mpa the same.After solid solution treatment and aging treatment of K418 alloy,boundary skeletal carbides changed to chains, the morphology of γ’ from the irregular stick to the rules of cube transformation, and size decreases with the increase of solution temperature. Exist the best heat treatment system: 1180 ℃ × 2 h(AC) + 930 ℃ × 16 h(AC), tensile strength,elongation and reduction of area of superalloy have a maximum value respectively: 821 Mpa, 6.0% and 5.7%. The group of dendrite is distributed in the sample’s center and fractured along the secondary dendrite root, and appeared a large number of torn edges and toughening around the fracture,the size of toughening nest is smaller and the more intensive, the plastic of alloy is better.After the melt superheat treatment of K418 alloy, the morphology of γ’are cubic shaped and irregular bulk, similar to the before overheating treatment. MC carbides change from Chinese characters skeleton type to chains. Comprehensive mechanical properties is reduced compared with the before overheating processing at room temperature, strength, elongationand hardness decrease about 24%, 50.9% and 5.5% respectively. K418 alloy Primary carbide MC react with γ solid solution, generating γ’ and M6C/M23C6 of small granular or flake after the heat treatment. Strength,elongation and hardness decrease about 18.1%, 43.4% and 10.7%respectively compare with the cast alloy when the induction heating power is 40 KW.After the melt superheat treatment and compound molten salt purificated of return F418 alloy, the size of γ’ is increase, C, S, N content and hardness are decrease. C, S, O, N content are reduce when the overheating temperature is 1480 ℃, reduce about 51.9%, 76.9%, 5.6% and75.4% respectively compared with F418 original alloy sample composition.Hardness decreased by 10.9% compare with the same.