Research On Co-based Selflubricating Composite Coatings By High Frequency Light Vibrating Assisted Laser Cladding

The metal-based self-lubricating composite coating is beneficial to improve the tribological properties of the metal surface due to the mechanical properties of the metal matrix and the tribological properties of the lubricated phase.It shows great superiority in the condition of no lubrication medium or lubricant medium failure.In the present research,WS₂,Nb C and Stellite 6 were used as cladding materials,Cr S/Nb C Co self-lubricating composite coatings were successfully fabricated on the surface of Cr12Mo V by laser cladding and high frequency micro-vibration assisted laser cladding.The effects of the addition of ceramic particles and the applied high-frequency vibration on the microstructure and properties of laser cladding self-lubricating composite coatings were explored,respectively.Based on the experimental results,it was found the self-lubricating composite coating that contains solid lubricated Cr S can be prepared on Cr12Mo V die steel surface by laser cladding WS₂/Stellite 6 composite powder.However,the content of Cr S in the coating is small,but the addition Nb C can effectively increase the Cr S content and improve the Cr S distribution in the coating.The frequency vibration assisted laser cladding process can improve the forming quality of the composite coating,and the prepared composite coating has a smooth surface,tight tissue and no cracks and holes.The coatings prepared by direct laser cladding has the continuous dendrites,and the dendrites become larger form the upper to bottom of the coatings.Besides,many black round Cr S and irregular Nb C distributed evenly in the coating.Moreover,the amount of Cr S in coatings increased with the WS₂increase in the mixed powder.The crystal structure broken and the dendrites become smaller form the upper to bottom of the coating prepared by high-frequency micro-vibration assisted laser cladding.With the increase of WS₂ in the cladding powder,the size and content of Nb C and Cr S gradually became smaller.For the coating with 20wt.%WS₂added,no Cr S are formed in the coating,broken dendrites and large amount of particle agglomerates appear in the upper of the coating.The composite coating prepared by direct laser cladding has higher microhardness,when the content of WS₂ in the mixed powder are 10 wt.%,15 wt.%and 20 wt.%,the average microhardness of the composite coating were 587.3 HV_0.5,546.6 HV_0.5 and 534.6HV_0.5,respectively.The strengthened phase Nb C and the refined matrix structure promote a higher hardness.While,the synthesized lubricating phase Cr S causes a slight decrease in the microhardness of the composite coating.The microhardness of the coatings prepared by high-frequency micro-vibration assisted laser cladding decreased slightly from the surface to the bottom of the coating.High-frequency micro-vibration slowed down the change trend of microhardness near the interface,and the microhardness decrease gradually from the coating to the interface.In the sliding friction and wear test,the self-lubricating composite coatings prepared by the two processes showed excellent wear resistance.The coating with powder composed of 60 wt.%Stellite 6,30 wt.%Nb C and 10 wt.%WS₂ has the best wear resistance,the average friction coefficient and wear rate were 0.421 and 5.6×10^-5mm³/N·m,the wear resistance is about 4.3 times that of Stellite 6 coating due to the relatively hard phase of Nb C and the solid lubricating phase Cr S.The high-frequency micro-vibration assisted laser cladding process can improve the tribological properties of the composite coatings,making the coating friction coefficient more stable and the wear surface smoother in the wear process.