Optimization of Plasma Spray Process Using Statistical Methods
- PDF / 1,092,492 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 95 Downloads / 198 Views
JTTEE5 21:176–186 DOI: 10.1007/s11666-011-9700-7 1059-9630/$19.00 ASM International
Optimization of Plasma Spray Process Using Statistical Methods F. Gao, X. Huang, R. Liu, and Q. Yang (Submitted July 15, 2011; in revised form October 9, 2011) The microstructure features of coatings produced by a plasma spray process are affected significantly by the process parameters such as powder size, spray gun nozzle size, total plasma gas flow, ratio of H2 + N2 over total gas flow, and so on. This article presents a study of the effects of these parameters on the microstructure (porosity, formation of crack, unmelted particle and oxide phase) of NiCrAlY coatings deposited by the Mettech Axial IIIÔ System. A Taguchi array is used to design the spraying process parameters. The results of the microstructure evaluation are used to generate regression equations for the prediction of coating microstructure based on process parameters. The results predicted from the regression equations are in good agreement with the experimental results according to a confidence level of 0.95. Among the parameters examined, the powder size and the ratio of H2 + N2 over total gas flow rate are the most significant parameters affecting the occurrence of crack, porosity, unmelted particle and oxide. Within the range of the designed process parameters, lower powder size and higher ratio of H2 + N2 over total gas flow rate lead to less cracks, pores, unmelted particles but more oxides. Nozzle size has marginal influence on oxides which increase with nozzle size. Gas flow rate has no direct influence on any coating feature evaluated with the range of variation.
Keywords
axial injection, crack, NiCrAlY coating, oxide, plasma spray, porosity, process optimization, regression equation, Taguchi method, unmelted particle
1. Introduction Plasma spray is one of coating deposition processes in which molten, semi-molten or solid particles are deposited onto a substrate. It uses ionized gas to accelerate the feed powder particles while heating them at the same time. The temperature of a plasma jet depends on the degree of ionization of plasma gas and the parameters of the plasma torch. To varying degrees, all process parameters contribute to the in-flight particle temperatures and velocities during spraying and in turn influence the coating features, such as density, defects and oxide formation, deposition efficiencies, as well as distortion and stresses experienced by the coated components. Attributes of powders and powder feed conditions also play an important role in evolution of the coating microstructure. Particle temperature is an important factor determining splat spreading and solidification and subsequently the coating density, as viscosity and surface tension decrease with rising F. Gao, X. Huang, and R. Liu, Department of Mechanical and Aerospace Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada; and Q. Yang, Institute for Aerospace Research, National Research Council of Canada, 1200 Montreal Road, Ottawa, ON K1A
Data Loading...
