Study On Microstructure And Properties Of Particle Reinforced Titanium Matrix Composites By TIG Arc Additive Manufacturing

Titanium and titanium alloys have high strength,high thermal strength and excellent corrosion resistance,but poor wear resistance and low hardness limit their application range.Adding ceramic particle reinforcement in titanium alloy to generate titanium matrix composites containing reinforcement phase in situ can make up for the deficiency of titanium alloy itself,enhance its wear resistance,hardness and so on.The chemical and physical properties of titanium matrix materials are different from those of reinforced materials,which increases the production difficulty and efficiency of particle reinforced titanium matrix composites.Additive manufacturing technology which integrates material preparation and shape manufacturing is predicted to resolve the problem of problematic processing and forming.In this paper,TIG arc additive manufacturing technology and flux cored wire technology are used to generate Ti B and Ti C reinforcement phase in situ by flux cored wire with B4C reinforcement particles in the arc fuse process,so as to enhance the wear resistance and hardness of titanium matrix composites.In this thesis,based on TIG arc additive manufacturing technology and flux cored wire technology,titanium matrix composites with particle content of 5 wt.%and 10 wt.%B₄C were fabricated layer by layer,and the composition,distribution and formation mechanism of reinforcement phase generated in situ were studied to explore the influence of reinforcement particle content in the wire on the wear resistance and mechanical properties of the molded parts.The effects of heat treatment parameters on the reinforcement phase distribution and mechanical properties of titanium matrix composites were analyzed.Through the experimental test of the molded sample,it is found that when the mass fraction of B₄C particles is 5 wt.%and 10 wt.%,the enhanced phase Ti B and Ti C originally generated by the reaction are distributed in grid shape.The microhardness of the molded parts increased from 456 HV_0.2 with 5%reinforcement content to 492 HV_0.2 with 10%reinforcement content;the friction coefficient of samples with various process parameters ranged from 0.45 to 0.47,and the wear amount of the molded parts decreased from44.7mg with the reinforcing particle content of 0%to 21.6mg with the reinforcing body content of 10 wt.%.The friction performance of the molded parts has been greatly improved.In order to explore the complex internal physical mechanism of particle reinforced composites manufactured by arc additive,the finite difference method is used to establish a three-dimensional multiphase flow model for the coupling of molten pool and reinforcement phase,the free surface of molten pool was obtained by Tur-VOF method,and the liquid-solid interface was processed by enthalpy porosity method,and the fluid dynamics model of molten pool flow was established.The model takes into account arc pressure,electromagnetic force,surface tension,gravity（buoyancy）,droplet transition,and droplet impact on molten pool.The heat transfer and interaction between the reinforcer and the molten pool are considered by tracking the reinforcer in the molten pool through the discrete phase model.Based on the above model,the flow of molten pool,the trajectory and distribution of particle reinforcer in molten pool,and the action mechanism of particle reinforcer on molten pool liquidity were calculated and predicted,and the distribution law of particles with different contents in molten pool was explored.