| Titanium alloys have excellent properties such as low density,high strength,heat resistance,and corrosion resistance,and are widely used as important high-temperature structural materials in aerospace and other fields.However,the low surface hardness,poor wear resistance,and easy oxidation under high temperature（≥700℃）conditions of titanium alloy seriously restrict its further application.In recent years,the rapidly developing high entropy alloy materials have shown excellent high-temperature mechanical properties.Coating them on the surface of titanium alloys to form a protective coating is expected to improve the comprehensive performance of titanium alloy substrates.This article takes TC4 titanium alloy as the matrix material,and based on the theoretical criteria for the formation of high entropy alloys,selects AlTiVCr,AlTiVNb,and AlTiVCr Nb high entropy alloys as the research objects for coating materials.Laser cladding technology is used to melt the high entropy alloy powder,achieving metallurgical bonding between the coating and the matrix.Exploring the forming quality,phase composition,microstructure characteristics of cladding coatings,and exploring the influence law and mechanism of material composition.Examining the microhardness,friction and wear,and high-temperature oxidation resistance of coatings,revealing the friction and wear mechanism and high-temperature oxidation resistance mechanism of cladding coatings.The main research results obtained are as follows:（1）High quality AlTiVCr,AlTiVNb,and AlTiVCr Nb high entropy alloy cladding coatings with good metallurgical bonding with TC4 substrate were obtained using laser cladding technology under optimized process parameters.The coating AlTiV-X（X=Cr,Nb,Cr-Nb）consists of a dark gray BCC matrix phase and a light gray dendritic and needle shaped coatingα-Ti phase composition.The addition of elements such as Cr,Nb,and Cr-Nb did not change the phase composition of AlTiV based alloys,but had a certain impact on the microstructure of the coating.The dendritic crystals on the surface of AlTiVCr,AlTiVNb,and AlTiVCr Nb coating gradually grew,and the needle like structure changed from dense to sparse.（2）The microhardness curves of AlTiVCr,AlTiVNb and AlTiVCr Nb high entropy alloy coatings are ladder shaped distribution in the cladding zone,Heat-affected zone and the matrix.Compared with the matrix,the hardness values of AlTiVCr,AlTiVNb and AlTiVCr Nb high entropy alloy coatings are 1.46,1.42 and 1.40 times of the matrix respectively.In addition,the relative wear resistance of high entropy alloy coatings AlTiVCr,AlTiVNb,and AlTiVCr Nb increased sequentially,all more than twice that of the substrate,with a maximum of 2.78 times.The wear mechanisms of TC4 substrate and the three high entropy alloy coatings are mainly adhesive wear,abrasive wear,and oxidation wear.（3）The oxidation resistance of laser cladding AlTiVNb,AlTiVCr Nb,and AlTiVCr high entropy alloy coatings gradually improves and is significantly better than that of TC4 matrix.After insulation for 100 hours in an atmospheric environment of 800℃,the oxidation weight gain of AlTiVCr was only 12.53 mg/cm-2.In addition,each coating exhibits obvious layering after oxidation,consisting of three parts:an external oxide layer,an internal oxide layer,and an unoxidized high entropy alloy cladding layer.The formation of an oxide layer effectively hinders the diffusion behavior of oxygen atoms,thereby improving the oxidation resistance of the coating. |
