Friction and Wear Behaviors and Damage Mechanisms of Different Friction Pairs Based on Hard WC Coating
The WC-12Co metalloceramic coating is regarded as the ideal choice to improve the wear resistance of engineering components.However,the friction and wear characteristics of the coating are not only related to its structure and components,but also closely associated with the friction pairs and working conditions.Thus,the work aims to expound the relationship between the mechanical and tribological properties of the hard WC-12Co coating sliding with different friction pairs.In this work,the WC-12Co coating was prepared by the high velocity oxygen fuel(HVOF)spraying technology,and then its morphology,phase composition and element distribution were analyzed by SEM,XRD and EDS.Meanwhile,the tribological properties and friction and wear mechanism of the coating sliding against three different coupled balls of GCr15 stainless steel,WC-6Co and Al2O3 were studied as well.Moreover,the friction and wear mechanisms were analyzed from the evolution of microstructure,mechanical properties and phase components.The elements and phases of WC-12Co coating prepared by HVOF technology were evenly distributed.The interior of the coating was uniform and compact with an average porosity of(2.86±0.16)％,while the near-surface layer was loose.This was caused by the tamping effect because of subsequent particles compacting the previous deposited particles.In addition,there was a slight decarbonization during deposition proved by the presence of W3C phase in the coating.The WC-12Co coating had a microhardness of about 1 103.8HV0.3,and a nano-hardness of about 20.47 GPa.According to the order of GCr15 stainless steel,WC-6Co and Al2O3,the microhardness,contact stiffness,nano hardness,elastic modulus and resilience of the coupled balls gradually increased,while the mechanical properties of the coating were slightly less than the values of the WC-6Co coupled ball.The dry coefficient of friction(COF)of WC-12Co coating sliding against different friction pairs was above 0.80,and the wear rate(WR)was in the order of 10-6 mm3/(N·m).The lowest COF was about 0.81 when the coating slid against alumina ball,and the highest COF was about 0.85 when the coating slid against tungsten carbide ball.The coating had the highest WR(11.09×106 mm3·N-1·m-1)coupled with aluminum oxide ball,and the lowest WR(1.60×10-6 mm3·N-1·m-1)coupled with GCr15 steel ball.Due to the low hardness and large plasticity of GCr15 stainless steel ball,the transfer film was easy to form and adhere to the coating surface during friction,appearing typical abrasive wear and adhesive wear characteristics.The mechanical properties of WC-6Co ball and coating were approximate,and there were no typical signs of abrasive wear or adhesive wear.The alumina would appear moisture absorption phenomenon in the air,and the formation of intermediate products could play a lubricant effect to reduce the COF.However,the hardness of Al2O3 ball was very high,and it was easy to wear the softer one of the friction pairs,so the wear rate of the coating was the largest.Besides,the tribochemical reactions of the coating sliding against different coupled balls were roughly the same.In general,the WC-12Co coating is dense and uniform with excellent mechanical properties.Although the COF and WR of the coating are slightly different due to the wear mechanism difference with different coupled balls,the wear resistance of the hard WC-12Co coating is very excellent.The various friction pairs can be selected according to the characteristics of the actual application conditions,so as to ensure the safe,stable and long-term service of the hard WC-12Co coating.
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