Residual Stress in HVOF Thermally Sprayed WC-10Co-4Cr Coating in Landing Gear Application

Type “N” Almen strips were HVOF thermally sprayed WC-10%Co-4Cr coating with spraying parameters used for landing gear coating production. The Almen strips were coated at variable passes and different cooling conditions. Deflections of Almen strip specimens were measured, and the coating residual stresses were calculated. With the same facility and spraying parameters, in situ coating property sensor was also used to continuously monitor the curvature of beam specimens being coated during and after coating deposition to evaluate coating deposition stress and final residual stress. The experiments, together with micro-hardness test, reveal that peening action occurred in the current HVOF spraying is limited, and the residual stress in the coating is dominated by quenching stress and cooling stress. In this study, the substrate temperature of specimens was adjusted by cooling air flow and torch recess time in between spraying passes. The coating residual stress demonstrates to apparently relate the substrate temperature because it significantly affects the cooling stress. Since the spraying parameters are frozen in industrial coating production, the cooling condition is a feasible approach for tailoring the coating residual stress.