Effect of surface orientation on characteristic weld microstructure evolution of Ni-base superalloy single crystal

Abstract

This chapter discusses the effects of surface orientation on characteristic weld microstructure evolution of Ni-base super alloy single crystal. The weld ability of Ni-base super alloy single crystal is investigated under various laser welding conditions by using the specimens with characteristic surface orientations. The conditions for prevention of cracks and/or different crystals evolution are established. The evolution of different crystals increased with increases in welding speed and laser power. This is attributed to the suppression of solid-solution of carbides during welding. Different crystals are formed due to easier heterogeneous nucleation from the vicinity of carbides at the fusion boundary. The effect of crystallographic surface orientation on the occurrence or prevention of different crystals is confirmed and interpreted in terms of different angles between orientations and thermal gradient direction. The thermal efficiency of gas turbine and jet engine is mainly influenced by the turbine inlet temperature. Thus Ni-base heat resistant super alloys are used for turbine blades and vanes because of their excellent high temperature mechanical properties and, in particular, their exceptional high temperature creep resistance.