Microstructure And Properties Of Ti-B/Ti-Ni Composite Coating Prepared By Electroplating And Laser Remelting On TA2 Surface

Titanium and titanium alloy is a kind of structural metal with light weight,high specific strength and good corrosion resistance.Because of its excellent comprehensive performance and huge development potential,it is widely used in many industrial manufacturing fields related to national economic lifeline.However,due to its unavoidable problems such as low hardness,high surface friction coefficient and poor wear resistance,the further application of titanium and titanium alloys has been restricted.Surface modification can not only retain the performance advantages of titanium and titanium alloys,but also improve their surface properties at a lower cost,which has become one of the research hotspots in the application field of titanium alloys.In laser surface modification of titanium alloy,cladding materials are usually added by powder preset method,which is simple,practical and efficient.However,this method has some disadvantages,such as low density,weak binding force so that easy to cause spatter,introduction of impurities so that easy to produce porosity and inclusion defects.In this paper,electroplating and laser remelting were used to avoid the above shortcomings,and the microstructure and properties of the modified coatings were studied.In this experiment,commercial pure titanium TA2 with moderate comprehensive properties was selected as the experimental substrate,Ni-TiB₂pre-coating and Ni-B pre-coating were prepared by composite electroplating as cladding materials.The microstructure and properties of Ti-Ni intermetallic compound composite modified coatings reinforced by TiB whisker and TiB₂particles were studied.The microstructure analysis showed that there was obvious phase stratification in the composite modified coating,in which TiNi phase occupied most of the area from the surface to the bottom layer of the composite modified coating,while Ti₂Ni phase mainly existed in the bottom layer of the modified coating contacting with TA2 substrate,which was distributed in a slender strip shape,and there were clear interfaces between Ti₂Ni phase and the TiNi phase and TA2 substrate,respectively.TiB-TiB₂/TiNi-Ti₂Ni composite coating can both be obtained by laser remelting of Ni-TiB₂pre-coating and Ni-B pre-coating.The TiB whiskers in the composite coatings obtained by the former method were obtained by in-situ reaction of TiB₂and Ti,and TiB₂particles are reaction residues;the TiB whiskers and TiB₂particles in the composite coatings obtained by the latter method were obtained by in-situ reaction of B and Ti in one or more steps.The hardness and wear resistance of the composite coating are greatly improved by TiB-TiB₂ceramic reinforcement.After laser remelting Ni-TiB₂pre-coating,the hardness of the composite coating is as high as 9.07 GPa,336%higher than that of TA2 substrate,and 158%higher than that of pure Ti-Ni coating without ceramic reinforcement;while after laser remelting Ni-B pre-coating with different parameters,the hardness of the composite coating are increased by 322%?371%compared with TA2 substrate.In addition,the wear rate of the composite coating obtained by Ni-TiB₂and Ni-B pre-coating plus laser remelting are significantly lower than that of TA2 substrate,the former is reduced by88.93%,and the latter are reduced by 90.03%?93.17%,showing good wear resistance.