Basic Research On Particle-reinforced Titanium Matrix Composites Formed By Laser Selective Melting

Titanium and its alloys have broad prospects in aerospace,shipbuilding and other fields because of their low density and good corrosion resistance.However,their poor wear resistance limits their application in frictional environment.In recent years,selective laser melting technology has attracted wide attention because of its outstanding advantages in the traditional manufacturing method,which can not complete the manufacture of complex special-shaped customized structural parts.In this paper,Ti-TiN and Ti-TiB titanium matrix composites were prepared by selective laser melting technology combined with ex-situ and in-situ synthesis respectively.The effects of reinforcement content on microstructure,microhardness,wear resistance and corrosion behavior of the composites were emphatically studied.The following research results were obtained:In TiN reinforced titanium matrix composites produced by selective laser melting,TiN particles are uniformly distributed along grain boundaries of titanium matrix,and with the increase of TiN content(0?7.5 wt.%),titanium grains are significantly refined,and the microhardness of materials is also significantly increased,from(256±11)HV_0.2to(403±20)HV_0.2;In addition,due to the addition of TiN,the wear resistance is also greatly improved,and compared with CP-Ti,the wear resistance is increased by about 29.2%.For in-situ synthesis of Ti-TiB composites by selective laser melting,with the increase of TiB₂content(0?7.5 wt.%),the average grain width of?'-Ti decreases from1.03±0.24?m to 0.36±0.05?m,which is mainly due to the addition of TiB₂reinforcing phase,the grain refinement of?'martensite caused by high cooling rate during selective laser melting,the dispersion strengthening of unmelted TiB₂particles,and the solidification of TiB₂particles.In addition,the wear resistance of Ti-TiB composites increases with the increase of TiB₂content,which is about 32.6%higher than that of CP-Ti materials.Electrochemical tests were carried out on CP-Ti,Ti-2.5TiN and Ti-2.5TiB materials produced by selective laser melting after immersing in 3.5 wt.%Na Cl solution for 0 day,5 days and 10 days,and was compared their corrosion behaviors at different stages.When the immersion time is 0 day,Ti-2.5TiB has more corrosion centers and serves as the reinforcement of micro-cathode,which can accelerate its early dissolution and form passive film earlier,the results showed that it has better corrosion resistance than CP-Ti and Ti-2.5TiN.Compared with Ti-2.5TiB and CP-Ti,Ti-2.5TiN has better corrosion resistance after being immersed for 5 days and 10 days,which is mainly due to the existence of finer grains and?-TiN phase,which plays a positive role in improving the coupling strength,accelerating the early dissolution of titanium matrix and forming a stable passive film.