Microstructure And Properties Of Laser Cladding Ti/TiBCN Composite Coating On TC4 Alloy

Ti6Al4V titanium alloy is abbreviated as TC4 alloy,because of its high specific strength,high specific modulus,high elastic modulus,good corrosion resistance,good fatigue resistance and excellent biocompatibility in aerospace,aerospace and vehicle engineering,TC4 alloy has high specific strength,high specific modulus,high elastic modulus,good corrosion resistance,good fatigue resistance and excellent biocompatibility.Petrochemical and medical departments have a wide range of applications.However,the disadvantages of hardness,wear resistance,high temperature corrosion resistance and oxidation resistance limit its application in bearing parts and friction components.Therefore,the application of surface modification technology to improve the hardness,oxidation resistance and wear resistance of TC4 alloy has important practical significance.In this paper,TC4 alloy was used to prepare metal/ceramic composite coating on the surface of TC4 alloy by laser cladding.In order to improve the service properties of TC4 alloy,the following studies were carried out:?1?The influence of process parameters on the geometric characteristics of pure titanium coating was studied.The laser power?P?,the scanning speed?S?and the powder feeding rate?F?are the main parameters that influence the geometrical characteristics of the cladding layer.The results show that the linear fitting relation of clad height,clad width and clad depth is S^-3/4F,P^2/5S^-1/2F^1/5 and P^4/5S^3/5,and the correlation coefficient is R²=0.96,R²=0.98 and R²=0.94,respectively.The dilution rate and the wetting angle are important geometric characteristic values for determining the good metallurgical bonding of the cladding layer and the base material,the linear relationship of the fitted dilution rate is P^1/2S^-4/5F^1/10,the correlation coefficient is R²=0.88,but the wetting angle and the process parameter value do not fit the linear relation.The best process parameters were selected according to the proposed and developed linear results:the laser power P=1400 W,the scanning speed S=7 mm/s,and the powder delivery rate F=300 mg/s.?2?The effects of scanning rate on dilution rate,microstructure,microhardness and wear resistance of Ti/TiBCN composite coatings were studied.The results show that,when the scanning speed is gradually increased,the clad height,clad depth and clad width are gradually reduced,the dilution rate is the first to decrease and then increase.When the scanning speed is gradually increased,the microstructure of the coating from the coating area to the substrate area is gradually refined,and the density of the microstrcture is gradually improved.Holes and crack defects are first reduced and then increased.When the scanning speed reaches 7mm/s,the density of the coating is the highest and the surface is free of crack and hole defects;when the scanning speed reaches 7 mm/s,the microhardness value of the coating reaches the maximum of 1074.1 HV;when the scanning speed reaches 7 mm/s,the coefficient of friction of the coating is minimum 0.36,and remains stable during the sliding time;when the speed reaches 7 mm/s,the wear surface of the coating is smooth,with only a few small parallel plows,a small amount of wear particles and fatigue spalling,and the mass loss?1.35 mg?and the wear energy conversion?285.01 J?of the coating are the least,Therefore,when the scanning speed is 7mm/s,the coating obtains outstanding comprehensive mechanical properties.?3?The effects of the content of TiBCN ceramic powder on the microstructure and properties of Ti/TiBCN composite coating was studied.The results show that when the content of TiBCN increases from 0 wt.%to 90 wt.%,the clad height and the porosity decreases gradually.However,when the content of TiBCN is 60 wt.%,the microstructure of the composite coating is dense and there are no pores and cracks.The composite coating is mainly composed of dendrite and rod phase TiBCN,small white lump phase TiC,fine lamellar phase TiN,small and scattered white block phase TiB₂.In addition,there are a few short whisker Al₃Ti phases and uniform layer block TiAl phases.TiN is nucleated uniformly by Ti and N atoms dissolved in molten pool.In addition,with the increase of TiBCN content,the microhardness of the composite coatings increased gradually,and showed better corrosion resistance and wear resistance than that of the substrate.When the content of TiBCN is 60wt.%,the microhardness of the composite coating reaches the maximum value of 1596 HV,which is about 4.6 times as much as that of the substrate.The corrosion potential of the composite coating reached-1.258 V and the corrosion current density was 4.035×10^-5 A/cm²,which was one order of magnitude lower than the corrosion current density of the substrate?1.172×10^-44 A/cm²?;The wear surface of the composite coating is relatively smooth,the average friction coefficient is the smallest?0.18?and the wear loss amount?1.22 g?is only9/50 of the substrate?6.7 g?.