Low-cycle Fatigue Behavior Of The Ni718Coated With WC-17Co At Different Ambient Temperature

Surface protection is a necessary method for wear resistance of shaft journal,bearing and hub of gas turbine engine compressor. Chrome plate is one of thetraditional techniques for surface protection, nevertheless, having been alternated byothers, for its hazard of hydrogen embrittlement and―Cr+6‖pollution. At present,tungsten carbide coating deposited by high velocity oxygen fule (HVOF) spraytechnology has become the hot spot for hard chrome alternativation. To promote thenew technology utilization in the gas turbine engine, it was necessary to vertify thefatigue life of the coating at working condition. Generally speaking, compressorcomponents work at temperature ranging form room temperature to～300℃.Meanwhile the components, such as shaft journal, bearing and hub, bearedcycle-bending load during take off and landing process. For these reasons, a low-cyclebending fatigue test was designed to evaluate the security of the components coatedtungsten carbide coating. A Ni718alloy was used as base alloy and a WC-17Cocoating was deposited on the base metal by HVOF technology. In the current paper,the particle velocity and temperature were tested, and the effects of particle on-flightcharacters on coating structures were also discussed. It was the emphasis to analyzethe effects of the ambient temperature on mechanical properties and fatigue behavior.Further more, the fatigue property was optimized through the improvement of particleon-flight character.In the current paper, the relationship between spray parameters, on-flightcharacters and coating structure was established, and then the spray parameters wereoptimized. The nano-indentation, micro-indentation and beam bending methods wereused to evaluate the elastic modulus (E), fracture toughness (KIC) and critical releaserate of bond energy (GC). Further more, the effects of ambient temperature to coatingmechanical properties were analysis then leading out the reasons of the variety ofmechanical properties. A cantilever beam specimen was used to investigate the fatigueproperty. The results show that cracks generated on the coating surface, propagated inthe coating, and then extended along the interface, finally, permeated through thesubstrate alloy when met the defect of interface. The KICand GCdecreased withambient temperature increase, introducing the fatigue life deficit. The higher temperature or larger thickness resulted in larger fatigue life deficit.Based on the above results, this paper attempted to improve the KICand GCthrough particle diameter size optimization, achieving the popurse of fatigue lifeimprovement. The results show that the WC-17Co coating derived from largest sizeparticle exhibited more42%cycle numbers than that of original coating at roomtemperature. The coating derived from the particle with middle size exhibited thebetter stability of fatigue life. There was only25%life deficit of this coating at300℃, which was only about45%of the deficit value of original coating at the sameconditions.