Papers by Author: Shi Hong Zhang

Abstract: For the Improvement of wear and corrosion resistances of Inconel718 (In718) surface, high velocity oxygen fuel (HVOF) thermal spray coating of micron-sized WC-Cr-C-Ni powder was coated onto Inconel718 surface and laser heat-treatment of the coating was carried out. Porous coating of porosity 2.2±0.4% was prepared by HVOF coating, and it was improved by laser heat-treatment, reducing the porosity to 0.35±0.08%. Micro-hardness of laser heat-treated coating increased more than four times compared to the surface of In718. Friction coefficient decreased by HVOF coating and laser heat-treatment. Wear resistance improved, decreasing the wear depth by the coating and laser heating. The interface between coating and In718 was compacted, and elements diffused from both coating and inconel718 substrate to interface, forming metal rich buffer zone (interface) and enhancing the adhesion of coating. Corrosion resistance improved by coating in sea water 3.5% NaCl solution and in 1M HCl acid, but it worsened in 1M NaOH base. For the improvement of wear and corrosion resistances of Inconel718, HVOF WC-metal power coating and laser heat-treatment are recommended.

Abstract: Micron-sized WC-CrCNi powder (WC-metal powder, WC 68%, C 0.56%, Cr 21% Ni 6%) was coated onto magnetic shaft material Inconel718 (In718) surface using HVOF thermal spraying equipment for the improvement of the surface properties of the shaft. During the HVOF coating, metal carbides, such as WC and Cr₇C₃ decomposed to W₂C, metals and free carbon. The free carbon and the excesively sprayed oxygen formed carbon oxide gases and thus produced pores and voids in coating. The optimal coating process (OCP) that produced the lowest coating surface porosity and the highest surface hardness was determined by the Taguchi experimental program of nine processes for four spray parameters with three levels. Coatings with porosity 1.20±0.1% and hardness 1150±60 Hv were prepared using optimal coating processes. The coating was porous, but the hardness was improved approximately three times from 400±10 Hv (In718) to 1150±60 Hv (coating). Friction coefficients (FC) of the coating were lower compared with In718 at both 25°C and 450°C. FC decreased with increasing temperature from 25°C to 450°C for both In718 and the coating. Wear depths of coatings were smaller than those of In718 at both 25°C and 450°C. For the improvement of the surface properties and durability of the magnetic shaft, HVOF WC-CrCNi power coating was recommended.