EFFECT OF PROCESSING CONDITIONS ON STRUCTURE, PROPERTIES AND PERFORMANCE OF A NICKEL BASE CAST SUPERALLOY FOR HIGH TEMPERATURE APPLICATIONS

摘要

Nickel base cast superalloys exhibits excellent combination of high temperature strength, creep, fatigue as well as oxidation and corrosion resistance and find wide applications in aerospace gas turbine components. Depending upon the severity of environmental conditions in gas turbine, components are cast in equiaxed (EX) or directionally solidified (DS) modes and subsequently heat treated to achieve a wide variety of structure and properties. Accordingly, a study was undertaken to evaluate the performance of a cast Ni-base superalloy and an attempt has been made to correlate processing conditions, structure and mechanical properties. Under similar heat treatment conditions, the directionally solidified material exhibited 15% to 20% superior high temperature strength and creep properties as compared to the equiaxed product.The superior performance of DS material is attributable to more effective solutionizing of γ/γ~1 eutectic, absence of interdendritic microporosity and fineness of microstructural features, which can be correlated to the progressive solidification under steep thermal gradient during vacuum investment casting. The present paper highlights the structure property relations in a Ni- base cast superalloy, which was processed in equiaxed and directionally solidified castings, through investment casting route.