Thermal cycle tests of thermal barrier coatings in vacuum were carried out to investigate the characteristics of thermal cycle damage and the effect of compositional gradient on thermal cycle damage. Surface cracks vertical to the coating surface were nucleated during thermal cycling, while no interlamellar crack along the interface between coating layers was found in vacuum. The compositional gradient significantly reduced the size and number of surface cracks nucleated during thermal cycle. This significant improvement in thermal cycle damage due to the compositional gradient results mainly from the improvement of material properties. No degradation of thermal barrier property during thermal cycling in vacuum was observed.
