Appropriate WC content improving wear and corrosion resistance of Ti(C, N)-WC coating

Abstract: In order to improve the surface strength of the agricultural machinery key components, the in-situ synthesis of Ti(C,N)-WC composite coating with various WC contents was prepared on Q235B steel specimen surface by reactive plasma cladding technology. Firstly, raw materials were the titanium powder, graphite powder, TiN powder, WC powder and Ni60A powder, which were mixed according to the mass fraction ratio of 28:7:15:0:50, 28:7:15:6:44, 28:7:15:12:38, 28:7:15:15:35, 28:7:15:18:32. The five components of the powder were respectively placed in a planetary-type ball mill DQM, milled for 6 hours, were made a mixed powder paste with 504 of the glue which was the adhesive, and then were uniformly coated on the surface of pretreated Q235B specimen. Secondly, the five samples were placed in the vacuum drying oven and were dried under 80℃. By the plasma cladding technology that DML-300 plasma welding machine provided the heat source and the plasma arc single channel was used to scan to clad, the pre-coated raw material components occurred melting and chemical reaction and synthesized Ti(C,N) metal ceramic composite coating with different WC contents in situ. The morphology, microstructure, phase, wear and corrosion resistance of the Ti(C,N)-WC composite coating were analyzed by scanning electron microscope (SEM), X-ray diffractometer (XRD), micro hardness tester, abrasion testing machine and electrochemical workstation. The results indicated that the granular new phase Ti(C,N) were synthesized in-situ on Q235B steel during the plasma cladding process and the composite coatings were made, which were composed of hard phase, ring phase and binder phase, and had a good metallurgical combination with Q235B steel substrate. Appropriate WC content can promote the formation of ring phase, which effectively improved the wettability of the metal ceramic hard phase and binder phase, prevented the hard phase particles from moving closer to each other, inhibited the hard phase grain growth, and thus it played a role in the grain refinement and dispersion strengthening which improved the strength of the coating. When the WC content was 12%, the typical development of core-ring structure became perfect, and uniformly dispersed and embedded in the binder phase, and the grain was finest. When the WC content exceeded 15% and reached18%, the ring phase changed thick or incomplete, grain coarsening, the core-ring structure reduced and had the tendency of disappearing, composite coating appeared holes and cracks. The micro hardness, wear and corrosion resistance properties of the coating strengthened with the increasing of the added amount of WC, when WC content was 12%, the maximum and average hardness of coatings was HV0.52030 and HV0.51750 which was about 6 times the hardness of the substrate, the friction coefficient of coating was about 2/5 of the substrate, the wear loss of coating was about 1/16 of Q235B steel, the wear resistance of the composite coating was excellent. In 5% H2SO4 solution, the corrosion rate of the coating with WC content of 12% was 1/9 of Q235B, in 3.5% NaCl solution, the corrosion rate of coating with WC content of 12% was 1/4 of Q235B, so the resistant corrosion property of composite coating with WC content of 12% was optimal in acidic and sodium chloride environment. Ti (C,N)-WC composite coatings have better wear and corrosion resistance behavior than the substrate. The trial provides a experimental and theoretical reference for strengthening agricultural machinery materials.