Evolution of strain-induced precipitates in a molybdenum base Mo-Hf-C alloy

International Journal of Powder Metallurgy 21 The powder metallurgy processed molybdenumbase alloy Mo-Hf-C (MHC) has excellent properties at elevated temperatures and is therefore used as a structural material for forging dies and rotating X-ray anodes. The nominal composition of this Mo-base alloy is 0.65 at.% Hf and 0.65 at.% C. The micro structure in the as-sintered condition consists of a molybdenum matrix, hafnium-oxide particles (5–10 μm diameter), molybdenum carbide layers at the grain boundaries, and large, hafnium carbides (1 μm diameter, ~80 nm thick). The residual hafnium content in solid solution is ~0.10–0.15 at.%. After deformation and subsequent aging of the as-sintered material, strain-induced plate-like hafnium carbides from 10 nm to 100 nm in diameter are formed. Dislocations act as heterogeneous nucleation sites, while carbon is delivered by the dissolution of molybdenum carbides. The aim of this work was to study the correlation between the compressive strength and the evolution of the size distribution of small, hafnium carbides for MHC specimens aged under different conditions. Scanning and transmission electron microscopy were applied for the micro structural characterization, and the strength was determined via a deformation dilatometer. 2015 EXCELLENCE IN METALLOGRAPHY AWARD