Towards enhanced sintering resistance: Air-plasma-sprayed thermal barrier coating system with porosity gradient

Sintering is one of the major failure mechanisms of air-plasma-sprayed thermal barrier coating system (APS TBCs) during high temperature service. For better sintering resistance, the TBCs with compositional gradient has been developed and fabricated by using advanced feedstocks, e.g. rare earth element-doped and nanostructured powders. Herein, a structurally graded design is put forward to counteract the effect of sintering in a convenient and economic way. Sintering induced degradations, in terms of Young's modulus and thermal conductivity, are slower in graded porous TBCs, indicated by thermo-mechanical finite element analyses and verified by experiments. Furthermore, a new sintering resistance parameter is proposed to evaluate the sintering resistance of TBCs under experimental (isothermal) and service (thermally graded) conditions. It is shown that graded porous TBCs, with decreasing porosity from top to bottom, exhibits improved sintering resistance and overall performance for engineering application.