The Research On The Preparation Of ZrC Ceramic Coating By Pulse Discharge In Liquid

EDC (Electrical Discharge Coating), as a process different to conventionalmachining, has perfectly characteristics, which is greatly used in manufacturingmould,automobile industry and aviation field. But about preparing ZrC ceramiclayer by EDC, the research reporting is still insufficient. In this field the research isimportant to accelerate the development of EDC.In the paper, the ZrC ceramic layer was prepared by EDC with metal Zrelectrode in kerosene on 45 carbon steel surface. The phase structure of the layer wasdetermined by X-ray Diffraction (XRD). The surface morphology of the layer wasobserved by Scan Electron Microscope (SEM). The variation of the elements in thelayer was analyzed by energy spectrometer. The surface hardness of the layer wasobserved by MVK-H3 microhardness instrument. The friction and abrasion test of thelayer used MPX-2000 friction & wearing test machine. Then, the main performancesof layers were compared between ZrC and TiC. At last, The main conclusions are asfollows:The result shows that: By setting reasonable pulse parameters, ZrC layer can beobtained. The layer mostly comprises of ZrC. The surface of the layer is rich in Zr, butgradually the Zr decreases. It shows that the combine of the layer with the base isgood, which result from the heat diffusing and chemical metallurgy reaction. From thecoating to the substrate, the hardness of the coating is an average decline, thethickness of the coating is approximately 20μm, The surface hardness of the ZrC layeris up to 2000HV.The paper has discussed the effect of the parameter on the layer. The discussionshows that peak current and pulse on-time are the primary factors, pulse off-time anddepositing time have almost no effect on the hardness but thickness of the layer. Thecontrast about the properties of ZrC and TiC two ceramic layers shows: When thepeak current is 8A, TiC coating achieves the maximum of hardness; but if thehardness of ZrC coating achieves a maximum, peak current need 16A. When pulsewidth is 20μs, the hardness of TiC coating can achieve maximum; but if ZrC coatingachieves maximum hardness, pulse width is required for 60μs.The formation mechanism of the layer was also discussed. The main formation mechanical properties of the layer are electrochemistry reaction andmicro-electro-spraying. During pulse discharge, kerosene was decomposed and Zrmetal from electrode was molten by the high temperature of the plasma, then, C fromkerosene combined with Zr, and ZrC was created on the surface of the work-piecefinally.The orthogonal test results of ZrC and TiC coating show: Optimal dischargeparameters of the ZrC layer, peak current 12A,pulse width 40μs, pulse-off 100μs,discharge distance 20μm, coating hardness up to 2300HV above; Optimal dischargeparameters of the TiC layer, peak current 5A, pulse width 12μs, pulse-off 120μs,discharge distance 30μm, coating hardness up to 2200HV around. So ZrC coatingpreparation for the discharge energy is higher than TiC coating Preparation.In the end, the friction and abrasion properties of the layer were tested. Thecontrast about ZrC coating, TiC coating by EDC and 45 carbon steel shows: Theabrasion morphologies of two coatings are typical parallel-plowing, and abrasionmechanism is mostly grain abrasion. In the same conditions of wearing test, theweight loss of two layers' surface treated with EDC is about one eighth or one tenthof the weight loss without treatment. Surfaced coatings can make the surfacewear-resisting property of matrix material has been greatly improved.