Effect Of TiO₂ Content On Microstructure And Properties Of Laser Cladding AlTiVCr Lightweight High Entropy Alloy Composite Coating

Titanium alloys possess excellent properties such as low density,high yield strength,and good corrosion resistance,making them widely used in aerospace,automotive industries,and other fields.However,intrinsic characteristics such as low hardness,poor wear resistance,and inadequate high-temperature oxidation resistance significantly limit the application prospects of such materials.Studies have shown that using laser cladding technology to prepare protective coatings and combining in-situ reactions to generate reinforcing phases within the cladding layer is an effective way to improve the surface properties of titanium alloys.High-entropy alloy materials have excellent comprehensive properties and similar physicochemical characteristics to titanium alloys,making them ideal materials for preparing titanium alloy cladding layers.This study takes TC4 as the matrix and selects AlTiVCr lightweight high-entropy alloy as the research object based on material lightweighting considerations.The la ser cladding technology is used to melt the high-entropy alloy powder,and the metallurgical bonding between the cladding layer and the matrix is achieved after rapid solidification.Additionally,by introducing nanoscale TiO₂ particles,TiO and Al₂O₃ reinforcing phases are in-situ generated within the cladding layer to further optimize the comprehensive properties of the composite coating.This study explores the influence of the phase composition,microstructure,and TiO ₂content of the composite cladding layer on the solidification structure,examines the variation laws of the microscopic hardness,friction and wear resistance,and high-temperature oxidation resistance of the cladding layer with the change of material composition,and reveals the underlying mechanisms.The main research results are as follows:（1）The introduction of nanoscale TiO₂ particles in the cladding layer leads to the in-situ generation of TiO and Al₂O₃ new phases.As the content of nanoscale TiO₂ increases,the content of irregular particle shaped TiO₂ and flake like Al₂O₃ in-situ precipitates in the composite coating increases,and they are dispersed throughout the entire coating.From the bottom to the top of the cladding layer,the grain size shows a trend of first coarsening and then refining,and the grain size at the same position increases to a certain extent with the increase of the nanoscale TiO₂ content.（2）The laser-clad AlTiVCr lightweight high-entropy alloy coating significantly improves the surface properties of TC4 matrix.The addition of the cladding layer increases the microhardness by 18%,and the relative wear resistance is 1.22 times that of the matrix material.The in-situ generation of TiO and Al₂O₃ hardening phases by introducing nanoscale TiO₂particles further enhances the surface properties of the material.When the addition amount of nanoscale TiO₂ is 9.49 wt.%,the average hardness of the coating reaches 774.3 HV0.1,which is 2.45 times that of the TC4 substrate,and the relative wear resistance is 1.55 times that of the TC4 substrate.In addition,the highest density of the obtained composite cladding layer is only4.96 g·cm^-3,still within the theoretical density range of lightweight high-entropy alloys.After being insulated in an atmospheric environment at 800℃for 100 hours,the oxidation weight gain of the TC4 substrate reached 53.55 mg/cm².The addition of lightweight high-entropy alloy composite overlay coating significantly improved the high-temperature oxidation resistance of the material.When the content of nano-TiO₂ was 9.49 wt.%,the oxidation weight gain of the material was only 0.42 times that of the TC4 substrate.