Near-Net-Shape Refractory Metal Products Produced by Plasma Spray Forming

摘要

Complex and thin-walled refractory metallic products such as molybdenum heating elements and tungsten crucible were fabricated using plasma spray forming (PSF) followed by hot isostatic pressing (HIPing). A lamellar structure consisting of vertical columnar grains, micron-sized pores, unmolten particles and rough interlamellar contacts with gaps of sub-micron sizes between lamellas were found in PSF molybdenum and tungsten deposits with relative density of 89.5% and 85.6%, respectively. During low-pressure HIPing, densification only took place in surface layers with gaps disappearing, while a large numbers of gaps and micro-pores retained in the inner layers. After two-step HIPing, lamellar structure of molybdenum products was not shown so distinctly, but it was still retained in tungsten ones. In addition, relative density, micro-hardness and ultimate tensile strength (UTS) of the products were increased with HIPing pressure and time.