Bulk microstructure evolution of two high Hf–containing nickel–based alloys during exposure at temperatures from 1100 to 1250°C

Two Hf–poorest versions of a high performance chromia–forming nickel–based polycrystalline cast alloy reinforced by HfC carbides were investigated by replacing more or less hafnium by tantalum to reduce production cost. After elaboration, microstructure control, thermal analysis and exposures at temperature were carried out on samples cut in the obtained ingots. The as–cast microstructures of the two alloys are similar to the initial alloy one but their behaviors at the three considered high temperatures (1100, 1200 and 1250°C) were more or less different: more fragmentation of the MC carbides and precipitation of chromium carbides during aging. Some decreasing effects on the room temperature hardness were observed, and one can suppose that the high temperature mechanical properties of these two {(Hf,Ta)C carbides}–containing alloys derived from the HfC–strengthened initial one may be lowered.