2015 EXCELLENCE IN METALLOGRAPHY AWARD EVOLUTION OF STRAIN-INDUCED PRECIPITATES IN A MOLYBDENUM-BASE Mo-Hf-C ALLOY

The powder metallurgy processed molybdenumbase alloy Mo-Hf-C (MHC) Dallinger,**** Helmut Clemens***** and Sophie Primig****** INTRODUCTION The particle-hardened alloy Mo-Hf-C (MHC) is processed via a powder metallurgy (PM) route. It is known for its high strength at elevated temperatures and its high recrystallization temperatures. Its nominal composition of 0.65 at.% Hf and 0.65 at.% C has been derived from various investigations of arc melted and solution-annealed Mo-Hf-C alloys in the 1960s and 70s. In particular, an alloy with a similar composition to MHC exhibited superior properties after swaging. In contrast to PM processed MHC, all the hafnium and carbon content of the solution-annealed material is in solid solution. The carbon and the hafnium contents of MHC are adjusted in order to produce ~1 vol.% hafnium carbide. 1-3 After sintering, the microstructure of MHC consists of a molybdenum matrix, hafnium-oxide particles (5-10 µm diameter), molybdenum carbides decorating 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.% and the typical microporosity is ~4%. For a full exploitation of the precipitation potential of the MHC alloy, it i