Flattening mechanism in thermal sprayed nickel particle impinging on flat substrate surface

摘要

The transition behavior of the splat pattern of nickel particles sprayed onto a flat substrate was investigated. Auger analysis and scanning electron microscopy observation of splats on a gold- coated substrate were examined. It was confirmed that splashing was not formed by flowing on the substrate surface from the impingement center to the periphery, but by jetting away from central disk. The etched splat surface revealed that the bottom part of the central disk of the splat solidified quiterapidly just after impingement onto the cold substrate. The splash pattern was found only in a direction perpendicular to the scratch pattern on the substrate. Therefore, it was confirmed that splashing was caused by some deterrent to the liquid flow, for example, due to effects such as poor wettability at the flow tip or initial rapid solidification of the splat. The drastic change of the splat pattern near the transition temperature seems to occur when the We number of the liquid flow coincides with some critical value.