Effect of microstructure and temperature on the erosion rates and mechanisms ofmodified EB PVD TBCs

摘要

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for anumber of decades and are now considered to be an accepted technology. As thereis a constant drive to increase the turbine entry temperature, in order toincrease engine efficiency, the coatings operate in increasingly hostileenvironments. Thus there is a constant drive to both increase the temperaturecapabilities of TBCs while at the same time reducing their thermalconductivities. The thermal conductivity of standard 7 wt% yttria stabilizedzirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can bereduced in two ways: the first by modification of the microstructure of the TBCand the second by addition of ternary oxides. By modifying the microstructure ofthe TBC such that there are more fine pores, more photon scattering centres areintroduced into the coatings, which reduce the heat transfer by radiation. Whileternary oxides will introduce lattice defects into the coating, which increasesthe phonon scattering, thus reducing the thermal conductivity via latticevibrations. Unfortunately, both of these methods can have a negative effect onthe erosion resistance of EB PVD TBCs. This paper compares the relative erosionrates of ten different EB PVD TBCs tested at 90à ° impact at room temperature andat high temperature and discusses the results in term of microstructural andtemperature effects. It was found that by modifying the coating deposition, suchthat a low density coating with a highly â  featheredâ  microstructure formed,generally resulted in an increase in the erosion rate at room temperature. Whenthere was a significant change between the room temperature and the hightemperature erosion mechanism it was accompanied by a significant decrease inthe erosion rate, while additions of dopents was found to significantly increasethe erosion rate at room and high temperature. However, all the modifiedcoatings still had a lower erosion rate than a plasma sprayed coatings. So,although, relative to a standard 7YSZ coating, the modified coatings have alower erosion resistance, they still perform better than PS TBCs and their lowerthermal conductivities could make them viable alternatives to 7YSZ for use ingas turbine eng