Abstract
An approach to the modeling of the process of the formation of thermal coatings lamellar structure, including plasma coatings, at the spraying of cermet powders is proposed. The approach based on the theoretical fundamentals developed which could be used for rapid and sufficiently accurate prediction of thickness and diameter of cermet splats as well as temperature at interface “flattening quasi-liquid cermet particle-substrate” depending on the key physical parameters (KPPs): temperature, velocity and size of particle, substrate temperature, and concentration of finely dispersed solid inclusions uniformly distributed in liquid metal binder. The results are presented, which concern the development of the computational algorithm and the program complex for modeling the process of laying the splats in the coating with regard to the topology of its surface, which varies dynamically at the spraying, as well as the formation of lamellar structure and porosity of the coating. The results of numerical experiments are presented through the example of thermal spraying the cermet TiC-30 vol.% NiCr powder, illustrating the performance of the developed computational technology.
Highlights
In the advanced technologies of thermal spraying, there is in most cases no possibility of in-process control of coating quality
That is why today the latter approach presents an independent theoretical rather than practical interest as modeling of several dozens or hundred thousand droplets interacting with the substrate or with the previously deposited coating layer will entail huge computational costs. An alternative to it is the use of experimentally validated theoretical solutions or semiempirical dependencies, allowing us to predict with an accuracy sufficient for practice the thickness and diameter of splats in some range of the key physical parameters (KPPs), which accelerates substantially the computational procedure of modeling the lamellar structure of coatings [15,16,17,18,19,20,21,22,23,24,25,26,27,28]
In order to make the datum-vertex array coordinates adequately taking into account the physical features of the cermet particle solidification process, in the formed splat two zones need to be distinguished: (i) a central zone formed by the splat core and presenting an inner disc, or some vicinity of the stagnation point, of diameter D0 = k1Dp and thickness hs, where k1 ∼ 1, and (ii) a peripheral annular zone bounded by two circumferences of diameters D0 and Ds
Summary
In the advanced technologies of thermal (including plasma) spraying, there is in most cases no possibility of in-process control of coating quality. An alternative to it is the use of experimentally validated theoretical solutions or semiempirical dependencies, allowing us to predict with an accuracy sufficient for practice the thickness and diameter of splats in some range of the KPPs, which accelerates substantially (by several orders of magnitude) the computational procedure of modeling the lamellar structure of coatings [15,16,17,18,19,20,21,22,23,24,25,26,27,28] As it was noted in paper [2], presently, a number of publications are available whose authors make attempt of theoretical and experimental generalization of splat diameters in thermal spraying of powder materials [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43]. This gives rise to a possibility of formulating the requirements for specific thermal spray facility and investigating its potential technological capabilities from the viewpoint of ensuring the given characteristics of the coating
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