Effect Of MoSi₂/MoS₂ On Microstructure And Properties Of Co-based Alloy Coatings By Plasma Transferred Arc Welding

In this paper,Co-based alloy coatings with different scanning speeds and different mass fractions of MoSi₂and MoS₂powders were prepared on Q235 steel surface by plasma transferred arc welding.The phase composition and microstructure of the coatings were analyzed by Ultima IV X-ray diffractometer,Zeiss optical microscope(OM),scanning electron microscope(SEM)and energy dispersive spectrum(EDS).The microhardness and wear resistance of coatings were tested by HV-1000 microhardness tester,wear tester and P7Tencor film profilometer.The analysis results were as follows.Co-based alloy coatings with different scanning speeds were mainly composed of?-Co and Cr₂₃C₆.After adding 5%MoSi₂powder,MoSi₂phase appeared in the coatings.The MoS₂phase was detected in the coatings by adding 3%MoS₂powder.The dendrite microstructure appeared in the Co-based alloy coatings.The refined microstructure was observed with increase of scanning speed.The dendrite was restrained with different growth direction after adding MoSi₂powder.The irregular microstructure appeared at the top of coatings by adding more than 5%MoSi₂.The black spherical substances appeared in the coatings by adding more than 5%MoS₂powder.The microhardness of coatings increased after increasing scanning speed.The microhardness of the coating with scanning speed of 220 mm/min was 91.81 HV_0.3,which was higher than that of the coating with scanning speed of 160 mm/min.The microhardness of coatings increased significantly with addition of MoSi₂powder.The average microhardness of coatings with 7%MoSi₂was 607.45 HV_0.3,which was 208.44 HV_0.3higher than that of Co-based alloy coatings.While the microhardness of coatings decreased with increase the content of MoS_2?The average microhardness of the coating with 7%MoS₂was 299.51 HV_0.3,which was 99.49 HV_0.3lower than that of Co-based alloy coatings.The friction coefficient and wear rate of coatings decreased gradually with the increase of scanning speed.At room temperature,the friction coefficient and wear rate of coatings decreased gradually with the increase of MoSi₂,and the wear mechanism was adhesive wear to abrasive wear.At high temperature,the friction coefficient and the wear rate of coatings decreased gradually,the wear mechanism was fatigue wear to oxidation wear and abrasive wear.The wear rate of coatings with the addition of MoS₂powder decreased first and then increased,and the friction coefficient of coatings decreased significantly.The wear mechanism was adhesive wear to abrasive wear.