Splat formation and microstructure development during plasma spraying: deposition temperature effects

Abstract It has been observed that substrate temperature has a dramatic effect in modifying the morphology of splats formed by impacting molten droplets on substrates during plasma spraying. This effect also has important implications on the deposit microstructure and properties. With an increase of substrate temperature from room temperature to a few hundred degrees (200–400°C), the splashing tendency is reduced and the splat morphology changes from fragmented to a contiguous disc-shape. Consequently, deposit microstructural integrity improves, and a number of properties are significantly enhanced with concomitant implications for coating performance. The mechanism of this splat morphology change has been subject of considerable investigation within the thermal spray community. It has been suggested by various researchers that the cause of this effect can be attributed to a number of factors such as: a higher solidification rate at the low substrate temperature; poor wetting and/or a contaminated substrate surface at lower temperatures etc. This paper summarizes, the experimental findings and reviews the various proposed hypotheses. The results are synthesized based on some recent experimental findings.

[1]  Jm Jos Houben.  Relation of the adhesion of plasma sprayed coatings to the process parameters size, velocity and heat content of the spray particles , 1988 .

[2]  R. C. Dykhuizen,et al.  Review of impact and solidification of molten thermal spray droplets , 1994 .

[3]  J. Szekely,et al.  Fluid flow, heat transfer, and solidification of molten metal droplets impinging on substrates: Comparison of numerical and experimental results , 1992 .

[4]  H. Herman,et al.  Rapid solidification and microstructure development during plasma spray deposition , 1996 .

[5]  P. Fauchais,et al.  Microstructural investigation of plasma-sprayed ceramic splats , 1997 .

[6]  C. Moreau,et al.  Influence of substrate preparation on the flattening and cooling of plasma-sprayed particles , 1995 .

[7]  Roger H. Rangel,et al.  Numerical simulation of substrate impact and freezing of droplets in plasma spray processes , 1993 .

[8]  P. Fauchais,et al.  Influence of particle parameters at impact on splat formation and solidification in plasma spraying processes , 1995 .

[9]  P. Fauchais,et al.  Parameters controlling the generation and properties of plasma sprayed zirconia coatings , 1995 .

[10]  C. Stow,et al.  An experimental investigation of fluid flow resulting from the impact of a water drop with an unyielding dry surface , 1981, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[11]  A. Frohn,et al.  The velocity change of ethanol droplets during collision with a wall analysed by image processing , 1993 .

[12]  Gerardo Trapaga,et al.  Mathematical modeling of the isothermal impingement of liquid droplets in spraying processes , 1991 .

[13]  C. Larsson.  Science and technology of surface coating: edited by B.N. Chapman and J.C. Anderson, published by Academic Press, London, 1974, 463 pp.; price £14.80. , 1976 .

[14]  M. Lieberman,et al.  Role of etch products in polysilicon etching in a high-density chlorine discharge , 1996 .

[15]  J. Matějíček,et al.  Substrate temperature effects on the splat formation, microstructure development and properties of plasma sprayed coatings: Part II: case study for molybdenum , 1999 .

[16]  Nickolas J. Themelis,et al.  TRANSPORT AND CHEMICAL RATE PHENOMENA IN PLASMA SPRAYS , 1997 .

[17]  J. Matějíček,et al.  Substrate temperature effects on splat formation, microstructure development and properties of plasma sprayed coatings Part I: Case study for partially stabilized zirconia☆ , 1999 .

[18]  M. Pasandideh-Fard.  Droplet impact and solidification in a thermal spray process , 1998 .

[19]  J. Madejski,et al.  Solidification of droplets on a cold surface , 1976 .