Study On Directed Laser Deposition Process And Mechanical Properties Of TiCp/TC4 Composites

With the increasing requirements for the stability and reliability of high-end components in aerospace and other fields,it is difficult for traditional alloys to meet stringent operational requirements.Although titanium alloys exhibit high strength,excellent corrosion resistance and other characteristics,their low hardness,poor wear resistance and thermal conductivity limit their application prospects,thus,there is an urgent need to compound with reinforced materials to improve its performance.Compared with casting,powder metallurgy and other traditional technologies,directed laser deposition technology can achieve near-net-shape titanium matrix composites parts with fine microstructure and good performance,which effectively improves the hardness,wear resistance and other properties of titanium alloys.In this paper,high-mass-proportion TiCp/TC4 composites were prepared by directed laser deposition,and the effects of TiCp ratio and laser energy density on the macroscopic morphology and microstructure of the composites were studied.This study was comprehensively concentrated on the effect of the process on the TC4 matrix,TiC reinforcement and the bonding interface,to reveal the interaction mechanism between the microstructure and mechanical properties.The main research contents and conclusions are as follows:?1?Dense 10-50 wt.%TiCp/TC4 composites samples without cracks were prepared by directed laser deposition to analyze the effects of TiCp addition and laser energy density on the macroscopic morphology and unmelted TiCp of the deposited samples.Within a reasonable process range,all TiCp reinforced composites have no macro cracks,and the relative density is above 98%.After adding more TiCp,unmelted TiCp increases gradually and distributes evenly.High laser energy promotes the melting of TiCp,which is helpful to reduce the amount of sticky powder and unmelted TiCp.?2?Based on the changes of the primary TiC,TC4 matrix and the bonding interface,the effects of TiCp addition and laser energy density on the microstructure of the composites were studied.After adding TiCp,it is found that the?-Ti grains are refined,the high-angle grain boundaries increases,and its texture is weakened;the size and content of primary TiC increase gradually,and some primary TiC has a certain orientation relationship with?-Ti,which indicates that the Ti phase can heterogeneously nucleate on the{111}densely packed crystal surface of the primary TiC.As the laser energy density increases,the nucleation rate of primary TiC increases and grows coarsely;when high laser energy deposited,the width of the C diffusion layer of unmelted TiCp increases,and the?-Ti grains tend to be refined;the lattice mismatch degree of some primary TiC and?-Ti is small,indicating that high laser energy is beneficial to heterogeneous nucleation of Ti phase.?3?The associated mechanism of the microstructure and mechanical properties of TiCp/TC4 composites was revealed.The increase of hard primary TiC increases the microhardness from 380.5 HV_0.2 to 730.2 HV_0.2,an increase is up to 92%;more primary TiC and unmelted TiCp participate in the abrasion,resist the squeezing and shearing effect of the abrasive on the matrix,thus,the wear resistance of the composites is significantly improved.However,the reinforced particles are intrinsically brittle,and the micro-cracks are continue to expand and merge during the stretching,resulting in a decrease in tensile properties from 950.5MPa to 515.5 MPa.Therefore,it is necessary to select the type of composite material and the deposition process after comprehensively tensile,wear and other properties according to operational requirements.