Warm Spray has demonstrated that it could fabricate comparatively dense metal coatings keeping with high purity during the atmospheric process. Its key technology is the control of the temperature of the supersonic combustion jet prior to supplying feedstock. So far, even titanium (Ti), known as one of materials difficult for the atmospheric process, could be deposited with less oxidation and higher density of the resulting coatings. For instance, the porosity and oxygen content of two coatings obtained were 2.3 vol% and 0.28mass%, and 1.1vol% and 0.92mass%, respectively. Further densification of Ti coatings was achieved by bi-modal size distribution of feedstock powder upon Warm Spraying in this study. When bigger Ti particles were mixed with the usual feedstock powder under 45 µm, the coating porosity was decreased to 0.8vol% simultaneously with the low oxygen content of 0.26mass%, which was comparable to the level of feedstock powder. This densification is caused by the balance of the enhancement of the peening effect by big particles and of optimization of the filling rate of the big and small particles.

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