Effect of Consolidation Temperature and Boron Addition on Microstructure and Mechanical Properties of Hot Isostatically Pressed PM Superalloy Based on ZhS6—K

Abstract

The chemistry of a high performance cast superalloy, ZhS6–K (Ni–10Cr–5Co–5W–5Al–3·5Mo–3Ti–0·2C–0·02B), was modified by slight reductions in carbon, titanium, and aluminium content and minor additions of niobium and hafnium. Two variants of the modified alloy chemistry with different boron contents (0·02 and 0·08 wt–%) were prepared by vacuum induction melting, argon atomization, and consolidation by hot isostatic pressing at three temperatures. It was observed that, unlike carbon, an increase in boron content did not promote the formation of continuous precipitates at the prior powder particle boundaries. Increased boron content narrowed down the consolidation temperature range and changed the morphology of γ′ particles from cuboidal to dendritic. Precipitation of an eutectic γ + γ′ structure and formation of continuous boride films at the grain boundaries severely degraded the mechanical properties of the high boron PM superalloy that was consolidated at a temperature marginally above the γ′ solvus. An optimum consolidation schedule was determined for the high boron alloy, which after a suitable heat treatment produced significant property improvement in stress rupture and tensile properties. PM/0416