High heat flux exposures of coated GRCop-84 substrates

The performance of several overlay coatings on Cu–8 at.%Cr 4%Nb alloy (GRCop-84) thermally cycled in a high heat flux hydrogen–oxygen combustion flame are reported. Finite element analyses (FEA) were conducted to evaluate the expected performances of coatings with different thermal conductivities as well as to determine a suitable thickness for coating deposition. Top coats consisting of Cu–26%Cr, NiAl and NiCrAlY along with a Cu–8%Cr bond coat were vacuum plasma sprayed on GRCop-84 thin sheet specimens. It was observed that the Cu–26%Cr coating formed blisters whereas the NiAl and NiCrAlY coatings showed no significant differences between the exposed and unexposed specimens. Water-cooled rectangular specimens specially designed to simulate a rocket engine liner were coated with a NiCrAlY-top coat using either a Cu–8%Cr or a Cu–8%Cr–1%Al bond coat. Preliminary tests conducted on these specimens showed no visible evidence of coating spallation after 40 cycles. The measured temperatures and heat fluxes were used in FEA models to estimate the stresses, strains and temperatures across the coating interfaces in these specimens.