Effect of substrate condition on splat formation during thermal spray deposition

Molybdenum and partially stabilized zirconia (PSZ) containing 8% Y₂O₃ splats were prepared on mild steel, glass and stainless steel substrates at several substrate temperatures. Their morphologies were analyzed using scanning electron microscopy (SEM) and 3-D surface profilometry. With an increase in substrate temperature from room temperature up to 400C, the shape of molybdenum splat on steel substrate changes from fragmented morphology to a more contiguous disk shaped morphologies; on glass substrate, molybdenum splats morphology changes from marginally splashing to disk-like morphology with the increase of substrate temperature. The flattening ratios of molybdenum splats are 2.4 and 4.5 on steel and glass substrates respectively; this difference is considered arising from the splat solidification velocity difference. With increased substrate temperature from room temperature to 400C, the PSZ splats morphology changes from splashing to disk-like, although significant amount of fragmented splats remains even at higher temperature. The average flattening ratio of PSZ splats made with substrate at 400C is 4.0. The mechanism of change in morphology of splats is discussed.