Effect of Deposition Rate and Deposition Temperature on Residual Stress of HVOF-Sprayed Coatings

In this paper, we examine the correlation between thermal spray process parameters that affect the deposition rate and the residual stress buildup in HVOF metallic and cermet coatings. Parameters of interest including feed-rate, raster speed, and substrate temperature (controlled via external cooling means) were evaluated in the context of their effect on the stress evolution in gas fuel HVOF-sprayed coatings. The process variables investigated are intended to change the deposition rate and subsequently the local deposition temperature (T_LD) at the location of impact. The residual stress during the deposition tends to be more tensile with increased T_LD, and this tendency is more significant when the change in T_LD is produced by the feed rate. Compressive stresses result for lower T_LD due to dominance of the peening effect. A systematic study of these effects was conducted for gas fuel HVOF-sprayed Ni- and WC-12%wt.Co-coatings. The Ni-coatings represent the family of ductile metallic materials, whereas the WC-12%wt.Co-coatings represent the behavior of hard cermets. Both materials develop compressive stress at low T_LD and change into tensile stress at high T_LD by manipulation of deposition rate parameters. Extensions to other materials and HVOF processes are also presented to support the analysis.