Near-Net-Shape Molybdenum Parts Produced by Plasma Spray Forming

Abstract

Complex and thin-walled refractory metallic parts including molybdenum (Mo) rocket nozzle and crucible were fabricated using plasma spray forming (PSF) followed by hot isostatic pressing (HIPing). Optical microscope (OM), scanning electron microscope (SEM), Archimedes method, Vickers hardness and tensile tests have been employed to study microstructure, density, micro-hardness and mechanical properties of the parts. A lamellar structure consisting of vertical columnar grains, micron-sized pores, partially melted particles and rough interlamellar contacts with gaps of sub-micron sizes between lamellae were found in PSF Mo deposits. Relative density, micro-hardness and ultimate tensile strength (UTS) of the deposits were about 89%, 150 HV 0:025 and 44 MPa, respectively. After low-pressure and two-step HIPing, those changed up to about 92%, 250$400 HV 0:025 (interior $ exterior layers), 93 MPa, and 97%, 325 HV 0:025 and 170 MPa, respectively. Moreover, a fourstage mechanism of HIPing for PSF parts including heating up, recrystallization, lamellae movement, plastic yielding and creep has been proposed and discussed in detail.

Near-Net-Shape Tungsten–Rhenium Alloy Parts Produced by Plasma Spray Forming and Hot Isostatic Pressing

“…They have studied operating parameters (plasma arc gas type and flow-rate, plasma gun nozzle size and spray distance) and their effects on density and microstructure of the deposits. Recently, 95W3.5Ni1.5Fe thin-walled products fabricated by PSF and vacuum liquid phase sintering were reported by Wang et al 12,13) The relations between microstructure and mechanical property before and after liquid phase sintering were investigated. A five-stage sintering mechanism (including solid state sintering and recrystallization, liquid phase formation and infiltration, solution and precipitation, particle rearrangement, solution-precipitation and coalescence) were firstly proposed and then double checked by experimental results.…”

“…and Wang et al 12,13) In the work of Wu et al, 9) technique of PSF for large-scale tungsten tubular heating elements was introduced. Rea et al 10) explored and characterized vacuum plasma spray formed tungsten parts reinforced by nanoscale HfC particles.…”