Thermal shock of functionally graded thermal barrier coatings with similar thermal resistance

An experimental study was conducted to develop an understanding of the thermal fracture behavior of plasma-sprayed yttria stabilized zirconia — NiCoCrAlY bond coat alloy compositionally graded thermal barrier coatings (TBC) when subjected to a thermal shock loading. For this purpose, two sets of two coating architectures with similar thermal resistances were studied. The thermal loading was applied using a continuous CO2 laser. The results showed that for a given thermal resistance, as the compositional gradation was increased, the maximum surface temperature at which horizontal cracks initiated in the TBC increased. Also, the final length of the horizontal cracks for a given maximum surface temperature decreased with increasing compositional gradation. It was concluded that the grading of thermal barrier coatings with similar thermal resistances brings about an increased resistance to interface cracking under thermal shock loading.