Microstructure and performance of in-situ synthesis Ti(C,N)-WC/Ni60A matrix composites coating

Abstract: The agricultural touching-cutter wears-out easily, fails frequently, has high costs and the service life is low. In order to solve these problems, a process of cladding ceramic coating on the metal surface is researched and developed against the agricultural mechanization situation. Using the DML-300 plasma welding machine, Ni60A based composite coating reinforced by in-situ synthesized Ti(C,N)-WC particulates was prepared on the surface of Q235B steel substrate by reactive plasma cladding technology. First, the titanium powder, graphite powder, TiN powder, WC powder and Ni60 powder was mixed 6 hours in the DQM planetary mill, the mass ratio was 28:7:15:12.5:37.5. The mixing powder was modulated into paste with the 504 glue as the adhesive. Then the mixing powder was put on the substrate of Q235B and the thickness was (2±0.5)mm, reserving 2-3 mm arc end. Finally, the specimen was placed in the electrothermal blowing dry box, heating up to 80℃. The plasma arc single channel was used to scan to clad, avoiding the thermal impact between each channel, during which the heat source was provided by the DML-300 plasma welding machine to melt and react between the depositing material components to synthesize composite ceramic coating in-situ. The plasma cladding technology parameters are: The scanning width of single channel is 4-5 mm; Working current is 200 A; Working voltage is 20 V; Argon is used as the shielding gas and the ion gas，the flow of them are 6-8 L/min, 0.6 L/min; Working distance is 4mm, Scanning speed is 150 mm/min. Composition, microstructure, organization and performance are analyzed by scanning electron microscope (SEM), energy disperse spectrometer (EDS), X-ray diffractometer (XRD), microhardness tester and metallurgical microscope. The results show that Ti powder, graphite powder, TiN powder of the pre-coated layer was synthesized in-situ granular new phase Ti(C,N) during the plasma cladding process. The new phase Ti(C,N) granules are uniformly dispersed in the cladding coating, and mainly form the core- ring structure composed of the hard phase, coated phase, and adhesive phase. Ti(C,N) and WC disperse uniformly in the Fe-Ni adhesive phase, Ti(C,N)-WC/Ni60A composite coating metallurgically combined with the substrate is prepared. Polygonal flake WC distributes in the cladding coating surface and the core-ring structure disperses among the adhesive phase of the subsurface. The surface hardness is bigger than the subsurface. The average hardness of the coating is HV0.51750, up to HV0.52040, and about 10 times of the microhardness of Q235B steel substrate. The strengthening mechanism of the cladding coating is both fine-grain strengthening and dispersion strengthening. The wear quantity of the cladding coating is about 1/6 of the new cutter material 65Mn steel. The wear mechanism of the cladding coating is mainly abrasive wear. There were not obvious existing furrows and the signs of wear and tear on the coating have a lower friction coefficient and an excellent dry sliding wear resistance. The plasma cladding Ti (C,N)-WC/Ni60A metal composite coating is not only suitable for operation under normal pressure (atmospheric pressure) with the excellent characteristics of the simple process, easy operation, low manufacturing costs and excellent performance of cladding layer, but also applies to wear-resistant strengthening treatment, repair and remanufacturing of agricultural touching-cutter.