Experimental and numerical investigation of porosity during low pressure plasma spraying of tungsten
- Univ. of California, Irvine, CA (United States)
Porosity plays an important role on the quality and properties of plasma sprayed materials. In this study, the evolution of porosity in low pressure plasma sprayed tungsten was investigated experimentally and numerically. Several experiments were conducted, including low pressure plasma spraying, followed by hot isostatic pressing (HIP). Quantitative characterization of porosity was conducted by using computerized image analysis. The porosity in the as-sprayed tungsten could not be reduced effectively by using a secondary hot working approach, such as hot isostatic pressing (HIP). Consequently, a theoretical and numerical analysis was undertaken in order to identify the mechanisms controlling porosity formation. The ultimate goal was to determine the optimal processing parameters to minimize porosity. The results of computations based on a unidirectional solidification model have shown that, under conditions representative of spray deposition processes, the high-velocity liquid metal spreading on top of the solidifying layer overflows, and re-attaches to the substrate at a further radial location where solidification also starts. A multi-directional solidification model has therefore been implemented to simulate the formation of possible pores, cavities and/or troughs. In the test case considered (high-velocity impact of a single tungsten droplet) no direct pore formation was observed. However, simulations predict the formation of an annular trough on the surface of the solidified splat. This feature may be a precursor of pore or cavity formation in multiple-droplet cases.
- OSTI ID:
- 237699
- Report Number(s):
- CONF-9510290--; ISBN 1-878954-58-X
- Country of Publication:
- United States
- Language:
- English
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