THE TEMPERATURE-VARIANT HARDNESS RESPONSE OF DUPLEX TBCS

The Vickers microhardness response of electron-beam physical vapour de posited (EB-PVD) and thermally sprayed duplex thermal barrier coatings has been investigated as a function of temperature. Hardness-temperat ure plots reveal a transition between a strongly temperature sensitive regime and an athermal regime, and this has been analysed using an ac tivation energy approach. The behavioural transition was found to be s imilar to 200 degrees C, with hardness falling rapidly above this temp erature to similar to 100 kgf mm(-2) at 800 degrees C in each case. Po st-annealing hardness-temperature response for the two coatings was ve ry similar despite significant differences in as-received hardness and microstructure. For the temperature-sensitive regime, activation ener gies for plastic deformation have been calculated as 61 kJ mol(-1) for EB-PVD and 79 kJ mol(-1) for the sprayed coating. Possible deformatio n mechanisms are discussed, as is the relevance of our data to possibl e in-service performance.