Ni–Co-Based Wrought Superalloys Containing High W—Microstructure Design for a Balance of Properties

Abstract

Ni–Co-based γ + γ′ superalloys were explored in a wide range of Co/Ni ratios for designing a wrought superalloy with a combination of superior high temperature strength and environmental resistance at temperatures above 927 °C (1700 °F). While alloys with high Co/Ni ratios possess superior creep resistance, reductions of the Co/Ni ratio and additions of Fe and B are effective in improving ductility in the intermediate temperature range and hold-time low cycle fatigue resistance. A formation of fine, discrete Co2W Laves precipitates covering a large fraction of grain boundaries is responsible for the improvements. The experimental alloys exhibited excellent oxidation resistance at 982 °C (1800 °F) by forming a protective alumina scale during cyclic exposure.