Influencing factors of stress rupture at 750 C temperature for cast nickel base superalloy K403

The standard heat treatment of cast nickel-base superalloy K403 is the solid solution treatment of 1210 C/4 h, air-cooling. It is very difficult to meet the requirements of the intermediate temperature stress-rupture life regulated by aviation standard HB5155. In order to resolve the above problem, some factors influencing intermediate stress-rupture life have been explored. The results showed that the intermediate temperature stress-rupture life have been explored. The results showed that the intermediate temperature stress-rupture properties impaired by treatment of 1210 C/4 h were due to precipitation of too small γ' phase (<0.2 μ m) in grains and absence of the secondary carbides at grain boundaries. The dendritic pattern appears at the fracture surface and there is no slip trace at the gauge length part of specimens treated by 1210 C/4 h, but the crystallographic plane at fracture surface and the extensive slip can be observed for the specimens treated by 1180 C/4 h. TEM results have shown that during intermediate temperature deformation the dislocation of 1/2 left angle 110 right angle moves to the interface of γ/γ' and cuts γ' phase to form the high energy antiphase boundaries. The finer γ can be cut and passed easily by dislocation and has a poor resistance to intermediate temperature creep. The finer dendrites and the microstructure containing intergranular M6C carbide with envelope of γ' and residual coarse γ' within grains were beneficial. Therefore high cooling rate during solidification and partial solid solution treatment of 1180 C/4 h are suitable for a turbine blade alloy K403. (orig.)