Effect of Heat Treatment on Mechanical Properties and Microstructure of Alloy 901

Two types of heat treatments are commonly used for alloy 901, one to optimize resistance to creep and rupture and the other, to improve tensile and fatigue properties. Solution and aging-treatment parameters (temperature, time, quench) for both types of heat treatment were varied within the ranges permitted by common specifications to define heat treatments resulting in improved combinations of room-temperature strength and ductility along with good stress-rupture properties. Room-temperature tensile and 1200°F stress-rupture tests were performed and microstructures were evaluated using light and electron microscopy. Structure/property relationships were defined. The results showed that relatively small variations in heat-treatment parameters resulted in significant differences in mechanical properties and microstructure. Room-temperature tensile properties were optimized without degrading 1200.'F stress-rupture properties. Mechanical properties were dependent on grain size and the characteristics of the grain boundary carbide and matrix hardening (y') precipitates.