Mechanism Research On Laser Cladding Pure Metalon Titanium Alloy

In order to better understand the mechanism of diffusion and interaction between eachelement under the condition of laser cladding,the cladding layer of pure metal powder（Fe/Cu/Cr）on Ti6Al4V titanium alloys substrate by laser cladding was investigated.Bycombining with the phase diagram and simulation of element diffusion during the solidify-cation process, the laser layer have been produced phase and the mechanism of each phasewas predicted.And analysis result can provide future theoretical guidance for powdermixture compositions as cladding material.Using pure metal powder is mainly for avoidingtoo many elements of the interaction to make analysis process complexly and impact theaccuracy of the results.Using thermodynamic phase diagram calculation software Thermo-Calc get the Fe-Ti-Al-V,Cu-Ti-Al-V,Cr-Ti-Al-V system equilibrium phase diagram． Base on the phasediagram analysis,using DICTRA software to simulate the element diffusion of solidify-cation process.Using HL-5000carbon dioxide laser as heat source,pre-placed Fe/Cu/Crpowder respectively on Ti6Al4V titanium alloy by laser cladding.The structure andcharacteristics of cladding layer were investigated by SEM, XRD and E-DAX.Meanwhile,the microhardness and friction and wear properties were studied.When the cladding material is pure Fe powder,the cladding layer phase consisted ofFeTi,Fe0.988Ti,Fe₂Ti.FeTi precipitation has three ways:First, w（Fe） is less than38wt.%,FeTi precipitation through the eutectoid transformation（β-Ti�'FeTi+-Ti）； secondly,when w（Fe） reach38wt.%⁴7wt.%,FeTi precipitation through eutectic transformation（Liquid�'FeTi+β-Ti）;lastly,when w（Fe） excess,Liquid transferred to Fe₂Ti through crystaltransformation,and residual Liquid with Fe₂Ti peritectic transformation （Liquid+Fe₂Ti�'β-Ti+FeTi） separate out FeTi. Fe0.988Ti is formatted the metastable phase is in the process ofexhalation FeTi.Fe₂Ti precipitate when the element Fe content in the system reaches42.7wt.%.When the cladding material is pure copper powder, the cladding layer phasecomposition is CuTi₂、CuTi₃、Ti（Cu、Al）2、Al2Cu3.CuTi₂precipitated from two approach:One is through eutectoid transformation（β-Ti�'-Ti+CuTi₂）when the systemcontent of Cu in less than20wt.%;Another way is eutectic transformation （Liquid�'β-Ti+CuTi₂）when the content of Cu in the system is more than40wt.%.CuTi₃precipitationmainly through the eutectoid transformation（β-Ti�'-Ti+CuTi₃）.When the cladding material is pure chromium powder, the cladding layer mainlyconsists of flake, dendritic and fine acicular structure.Dendritic structure main is enrich ofTi element,its growth mode is dendritic way to grow up.There are two main ways Cr₂Tigenerated, one is through the eutectoid transformation（β-Ti-Ti+-Cr₂Ti）when thecontent of Cr is less than15wt.%;another way is through the eutectic transformation（Liquid�'β-Ti+LAVES）when the content of Cr is more than15wt.%.There will be onlyCr₂Ti,no precipitation between Ti-Al intermetallic compound when the content of Cr inmore than60wt.%.Microhardness and wear resistance of the cladding layer is improved significantlycompare to substrate.The reinforcement mechanism is mainly: one is the cladding layerthrough rapid condensation occurred quenching, making microstructure fine, improve thecladding layer microhardness; Secondly, intermetallic compound has played a role toenhance the property and the interaction between intermetallic compound and solidifiedstructure have effect to fine grain refining strengthening.