Research On The Process And Properties Of Coatings On TA2 Surface By Electrospark Deposition

As an important structural metal,titanium has the advantages of high specific strength,low density and good toughness.Titanium is the key material for high performance engines to lose weight and increase thrust weight ratio,but titanium has low hardness,low thermal conductivity and poor wear resistance.When serving under high temperature,high pressure and air shock,the titanium alloy parts are easy to ignite,causing damage to parts and even burn the whole case.The preparation of flame retardant coating on the surface of titanium parts which is easy to friction is an effective way to prevent “titanium fire”.In this paper,the flame retardant coating was prepared on the surface of TA2,the preparation,microscopic characteristics and wear resistance of flame retardant coatings were studied.The WC coating was prepared on the surface of TA2 by DZ-4000 III spark deposition system.The effect of deposition voltage on the excess coefficient of WC electrode,micro morphology,surface roughness and thickness were studied,and the microhardness and residual stress of WC coating were measured.The results show that:when the deposition voltage is less than 60 V,the mass excess coefficient increases with the increase of voltage.When the deposition voltage is greater than 60 V,it decreases with the increase of voltage.At 60 V voltage,the mass coefficient is the largest,about 56%.The WC coating was continuous and compact,mainly composed of W2 C,TiC and W.At 60 V voltage.The coating has the least defects,the surface roughness of the coating is the smallest,Sa=7.287 ?m.The thickness is thicker,about25 ?m.The microhardness is about 970.5 HV.However,the thickness is thin,and there is a large residual tensile stress in many areas of the coating surface.In order to improve the thickness,the Zr/WC and CoCr/WC composite coatings were prepared by adding appropriate Zr and CoCr transition layer.The microstructure,phase composition,surface roughness,thickness,microhardness and residual stress of the composite coating were studied.The results show that the transition layer is well bonded to the substrate and the outer layer of WC.The surface of composite coating is flat and compact,and the microhardness is higher than that of the substrate.The thickness of Zr/WC and CoCr/WC composite coatings were 55 ?m and 60 ?m.Residual stresses exist in most areas of the composite coating,and a small part of the region has a small residual tensile stress.The friction and wear tests were carried out on the samples and substrates in order to study the wear resistance of the coating.The wear weight loss,wear scar morphology and wear scar profile were studied.The results show that the wear weight loss,wear volume and wear rate follow the following rules: TA2 > WC coating>Zr/WC composite coating > CoCr/WC composite coating.The wear of Zr/WC composite coating and CoCr/WC composite coating is slight,and the addition of transition layer is helpful to improve the wear resistance.