SIMULATION OF THE EFFECT OF CREEP ON STRESS-FIELDS DURING VACUUM PLASMA SPRAYING ONTO TITANIUM SUBSTRATES

Boron carbide has been deposited by vacuum plasma spraying onto thin s ubstrates of Ti-6wt.%Al-4wt.%V alloy. Substrate/deposit curvature hist ories have been measured by analysis of a series of video images. Thes e results, together with thermal histories, have been compared with pr edictions obtained from a numerical process model describing the devel opment of residual stresses. It is shown that, when using the standard form of the model, a discrepancy arises between predicted and observe d curvature histories. This is attributed to the effect of creep in th e substrate under the influence of the residual stresses. A modificati on to the model accounting for the effect of creep allowed good agreem ent to be obtained between theory and experiment. It is shown that cre ep effects can be significant with titanium, although they become less significant as the substrate thickness increases. In general, the eff ect of creep is to lower the stress levels during spraying, although t he final residual stresses can actually be higher than would be the ca se in the absence of creep.