Effects of the metal-ceramic transition region on the mechanical properties and crack propagation behavior of an Al2O3-40 wt% TiO2 coating

Abstract A modified coating system comprising a ceramic region, a metal-ceramic transition region (a region compounded with ceramic splats and NiAl splats) and a bond region is deposited by atmospheric plasma spraying (APS). The micro-structure and phase composition are studied using scanning electron microscopy and X-ray diffraction. The mechanical properties, stress distribution and crack propagation are evaluated with a bending test. At the same time, the thermal shocking resistance of the modified coating system (MAT40 coating system) is also estimated. The results show that the cracks are deflected by small NiAl splats and cross long NiAl splats after the large tensile deformation of the NiAl splats during bending test. In addition, the crack extends along the boundary of the columnar grain in the ceramic splats. The appearance of the transition region makes a toughness increase and stress gradient decrease. Net macro-cracks are observed at the surface of the Al 2 O 3 -40 wt% TiO 2 coating with a conventional dual layer structure system. However, in the modified coating system, we find almost no cracks after the 50th cycle of thermal shocking. In addition, the intergranular cracks taken place in the coating both under continuous thermal shocking circles and three bend test.