Grain morphology of molybdenum splats plasma-sprayed on glass substrates

Molybdenum particles were injected into a plasma flame within an atmospheric environment, melted and accelerated to impact on a glass substrate. Contiguous splats are formed on substrates maintained at 340 and 480°C. Grain structure of the oxygen-enriched molybdenum splats was observed with optical microscopy and scanning electronic microscopy. It was found that dendrite grains align along the splat rim towards the center, suggesting that solidification is initiated at the periphery of melt splat. The solidification starts after the splat has reached its final diameter. The grains in the central portion of the splat are predominantly equiaxed, indicating melt undercooling prior to solidification. The physical process associated with grain structure formation is discussed.