Study On Microstructure And Properties Of Plasma Cladding NiCr Based Diamond Reinforced Self-Lubricating Coating

The background of this paper is to improve the tribological properties of mechanical parts and reduce the energy consumption caused by friction.Gray cast iron HT250 was selected as the matrix material,NiCr alloy with high temperature and corrosion resistance was selected.Diamond with different particle sizes was added as reinforcing phase.Self lubricating phase WS₂ and Ce F₃ was introduced successively.Afterwards,plasma cladding coatings were prepared by adding magnetic field,which have excellent wear and friction reduction properties.Microstructure and properties were analyzed,including the changes of phase composition,microstructure and the improvement mechanism of wear-resistant and corrosion-resistant properties of the coating.1.The plasma cladding coating was prepared by adding micron/nano diamond into NiCr50 alloy powder.The phases of the cladding layer mainly includeγ-（Ni,Fe）,Cr_xC_y,（Fe,Cr）₇C₃ phase.Nano diamond is easier to form fine and uniform hard phase in the coating than micron diamond.The average hardness of micron and nano diamond reinforced cladding coating can reach 488.4HV_0.3、450.9HV_0.3.Compared with HT250 matrix,the improvement range can reach 96.0%and 81.0%.Compared with NiCr50 coating,the improvement range can reach 24.2%and 20.0%.The friction coefficient of 0.1 wt.%nano diamond coating is 0.446,the antifriction performance is better than that of NiCr50 coating,but the corrosion resistance is decreased.2.After adding WS₂ self-lubricating phase,Fe₃W₃C hard phase and Cr_xS_y lubricating phase were formed in nano diamond/NiCr50 coating,and the microstructure segregation was improved.The friction reduction and wear resistance of the coating were significantly improved.The friction coefficient was reduced to 0.353 for the coating with 5 wt.%WS₂,and the average microhardness was 551.9 HV_0.3.After adding WS₂,the passivation area was appeared and the corrosion resistance was improved.3.After adding CeF₃ rare earth self-lubricating phase,the microstructure of WS₂/diamond/NiCr coating was obviously refined,and the porosity of the coating decreases with the increase content of Ce F₃.The average hardness of the coating reached 722.4HV_0.3 after adding 2 wt.%Ce F₃.The coating with the best antifriction effect appeared in the addition of 1wt.%Ce F₃.The average friction coefficient was 0.381,and the wear weight loss was reduced from 1.2mg to 0.7mg.The curve remained stable with time,and the self-lubricating action time was prolonged.The corrosion potential of Ce F₃ coating was increased,the corrosion current density was decreased and the corrosion resistance was further improved.4.The microstructure of the coating prepared by external magnetic field stirring bath can be further refined.Compared with the longitudinal magnetic field,the microstructure distribution of the coating prepared by external transverse magnetic field is more uniform.When the transverse magnetic field strength is 46m T,the friction coefficient of the coating is the lowest,which is 0.327.The friction coefficient and weight loss increased at 400℃.The erosion wear resistance of transverse magnetic field coating is better than that of no magnetic field and longitudinal magnetic field coating.The weight loss of erosion wear is the lowest when the erosion angle is 30°,which is 60.7mg,and it is 44.4%lower than that of non magnetic field coating.