Abstract
Thermal spraying is a well-established surface modification technology which has been widely used in industrial applications. As the coating properties were mainly determined by the flattening nature of each splat, much attention has been increasingly paid to the study on the splat formation process of thermal sprayed particles. This paper is concerned with the development in the research of the splat formation process of the individual splat deposited by thermal spraying during the past few decades, including the experimental and numerical simulations up to today; some classical splashing models were also reviewed. As a simulation of the actual thermal spray process, the development of the flattening behavior of free falling droplet has been mentioned as well. On the basis of the current investigation, some recommendations for the future work have been advised.
Highlights
A transition phenomenon in a attening behavior of the thermal sprayed particle on the at substrate surface was rstly introduced in 1995 [17], which reported that when the substrate temperature was increased above one critical temperature, the splat shapes of most materials sprayed onto at substrates underwent a transition from a distorted shape with splash to a disk-shaped splat. e transition temperature, TTtt, as a critical substrate temperature over which more than 50% of splats are disk shaped, can be considered as a useful tool for the process control
The pore and grain distribution at cross-section of the individual splat was observed by the assistance of focus ion beam (FIB) and transmission electron microscopy (TEM) [12, 52, 86,87,88,89,90]. e results proposed that different microstructures could be found under designated conditions, the substrate chemistry, roughness, and temperature all play an important role in the splat formation process, but the substrate temperature effect is the most prominent of these
A splat formation model has been developed based on the classic nucleation theory accounting for heterogeneous nucleation kinetic and crystal growth to predict the nucleation temperature and grain size distribution [101], the in uence of the substrate material, interfacial thermal contact resistance, and wettability on the nucleation, grain size distribution, and rapid solidi cation process has been investigated
Summary
A transition phenomenon in a attening behavior of the thermal sprayed particle on the at substrate surface was rstly introduced in 1995 [17], which reported that when the substrate temperature was increased above one critical temperature, the splat shapes of most materials sprayed onto at substrates underwent a transition from a distorted shape with splash to a disk-shaped splat. e transition temperature, TTtt, as a critical substrate temperature over which more than 50% of splats are disk shaped, can be considered as a useful tool for the process control. It is assumed that the adsorption/desorption of adsorbates and condensates on the substrate surface [22, 29,30,31,32,33], surface characteristic change [33,34,35,36], and thermal contact resistance [37, 38], along with the wetting induced by the topography change might dominate the transition [45, 46] It is quite interesting and practically meaningful that the transition in the splat shape of an individual particle corresponds well to the transition in the adhesion strength of the coating fabricated at corresponding temperature conditions [13, 47]. Few interlocking might be formed. n other words, the existence of splash nger might be the weak point for the adhesive between splat and substrate surface
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