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The tungsten powder density of the feed stock used in Laser Powder Beam Fusing (LPBF) is an important parameter that influences not only the densification and performance of as-LPBF tungsten but also its microstructure, mechanical properties and other physical characteristics. Therefore, the development of a high-density tungsten feedstock with an ideal morphology has been one of the major research goals in tungsten LPBF.
A tungsten powder with an extremely fine particle size and an almost uniform distribution is required to ensure high densification in LPBF. However, the production of such a tungsten powder is not easy and requires complex reduction conditions such as hydrogen flow rate, boat loading volume, reduction time and temperature. A comprehensive study was conducted to investigate the effect of the above-mentioned factors on tungsten powder density and morphology, which concluded that the reduction temperature had the greatest influence on tungsten powder morphology while the hydrogen flow rate and the loading boat volume had a less significant impact.
As-LPBF tungsten blanks with relatively high density and good microstructure exhibit superior performance in terms of compressive strength, hardness and bending strength. The effect of the induced columnar grain direction on these performance parameters is also under investigation.
Studies have shown that a higher relative density of as-LPBF tungsten can be achieved by using certain process conditions such as a lower laser power, scanning speed, layer thickness, hatch distance and remelting scan sequences. In addition, a post-process treatment such as hot isostatic pressing or annealing can significantly improve the mechanical properties of tungsten LPBF components by reducing cracking.