High Temperature Creep Properties of K444 Cast Superalloy

The high temperature tensile creep behavior of a new type of cast nickel base superalloy K444 under the condition of 850~950 ℃/225~380 MPa was studied. The results show that the microstructure of K444 alloy was mainly composed of γ′phase, γ′/γ′ eutectic, carbides, nitrogen and boride. γ′ phase in heat treated sample had spherical and elliptical two forms. The γ′ particles started rafting in the end of deceleration period, and then interacted with the dislocation. Creep curves of K444 alloy had shorter initial stage and long acceleration stage, which resulted by the rafting of γ′ particles and the interaction of the dislocations. The accelerated creep should be strain softening stage, and it can be described by the formula of =min(1+c′Δε)exp(n′Δε). The creep rupture data complied with Monkman-Grant rules, and the void cracks originated from the boundary or branch grain boundary.