Simulation of the effect of creep on stress fields during vacuum plasma spraying onto titanium substrates

Abstract

Boron carbide has been deposited by vacuum plasma spraying onto thin substrates of Ti−6wt.%Al−4wt.%V alloy. Substrate/deposit curvature histories have been measured by analysis of a series of video images. These results, together with thermal histories, have been compared with predictions obtained from a numerical process model describing the development of residual stresses. It is shown that, when using the standard form of the model, a discrepancy arises between predicted and observed curvature histories. This is attributed to the effect of creep in the substrate under the influence of the residual stresses. A modification to the model accounting for the effect of creep allowed good agreement to be obtained between theory and experiment. It is shown that creep effects can be significant with titanium, although they become less significant as the substrate thickness increases. In general, the effect of creep is to lower the stress levels during spraying, although the final residual stresses can actually be higher than would be the case in the absence of creep.