Influence of Heat Treatment on Microstructure and Mechanical Properties of 4^th Generation DS Superalloys

Abstract

Ni-base directionally solidified (DS) superalloys have an advantage of production costs over single crystal (SC) superalloys because of better yield rate of casting and simpler heat treatment compared with SC superalloys. In this study, we designed a 4th generation DS superalloy, TMD-111, based on our 5th generation SC superalloy, TMS-162, containing 5 mass%Ru; we added C and B on TMS-162 to strengthen the grain boundaries. The alloy was directionally solidified and heat treated under four different conditions, i.e., as cast, as solution treated, solution treated and aged, and solution treated and two step aged. The solution treated and two step aged sample showed the highest creep strength, although the effect of heat treatment was found to be relatively small. All the samples except for as cast ones showed longer 1% creep strain under a 1100°C/137 MPa compared with that of CMSX-10, a typical third generation SC superalloy.