Microstructure Evolution of Fine-Grained Cobalt T400 Tribaloy Processed by Spark Plasma Sintering or Hot Isostatic Pressing of Gas-Atomized Powders

Abstract

Tribaloys are Laves phases-hardened cobalt alloys usually produced by casting. In order to obtain a finer and more homogeneous microstructure, powder metallurgy was used by gas atomization of T400 Tribaloy powders followed by either spark plasma sintering (SPS) or hot isostatic pressing (HIP). Quantitative characterization of the microstructure was performed with X-ray diffraction, electron microscopy combined with energy-dispersive X-ray spectroscopy, at all stages of the processes. The gas atomized powder presents a fine composite microstructure composed of eutectic Laves phases and cobalt solid solution. The fraction of Laves phases increases upon consolidation time and temperature, with a composition tending to Co3Mo2(Si + Cr). This results in a hardness between 60 and 62 HRC for Spark Plasma Sintered and Hot Isostatic Pressed parts, depending on the consolidation parameters. The high solidification rates of atomization combined with powder consolidation lead to a fine-grained alloy, more homogeneous than cast alloys for the same grades.