Effects of HVOF bond coat on thermal cyclic failure lifetime of thermal barrier coating

NiCoCrAlY bond coat (BC) was fabricated on the GH99 superalloy by high velocity oxy-fuel spray(HVOF) and air plasma spray (APS) respectively. Thermal cyclic failure of thermal barrier coating(TBC) with APS and HVOF BC were studied. The results show that the interface of APS BC is irregular with wave morphology, and it is relatively straight and uniform for the interface of HVOF BC. The ceramic top coat(TC) of TBC with APS BC partly spalled-off after 200 thermal cycles. Only micro-cracks were observed in the TBC with HVOF BC after same thermal cycles, and thicker layer of thermally grown oxide(TGO) formed. Most of the TC of TBC with APS BC spalled-off after 350 thermal cycles, however, after 430 thermal cycles, the propagation of micro-cracks led to the failure of TBC with HOVF BC. The residual stress analysis by Raman spectroscopy (RFS) shows that the residual stress of TBC with HVOF BC increased with increasing number of thermal cycle. The residual stress of TBC with APS BC reached a value of 650 MPa at 350 thermal cycles and that of TBC with HVOF BC only reached 571 MPa at 400 thermal cycles. Thermal shock resistance of TBC can be improved with NiCoCrAlY bond coat perpared by HVOF technology.