Research On Modification Of In Situ Synthesized Ti₃Al Based Ceramic Composite Coating On Titanium Alloy Surface By Laser Cladding

Titanium and titanium alloys are excellent lightweight structural materials and are widely used in aerospace,petrochemical,automotive,and biomedical engineering.However,the poor wear resistance and low hardness of the titanium alloy limit its scope of use,especially in the wear of structural components.The use of laser cladding technology in the titanium alloy surface cladding metal-ceramic mixed powder can be obtained composite coating,and this composite coating has both good toughness of the metal coating characteristics,but also ceramic coating wear and corrosion resistance characteristics.As a result,the surface properties of the titanium alloy material can be improved,and thus it has a very important application value.In this paper,TC21 titanium alloy as the matrix material,Ti,Al,BN,Ce O₂ powder as cladding material,the use of laser cladding technology in situ synthesis of Ti₃Al-based composite coating on the surface of the alloy.X-ray diffraction,scanning electron microscopy and electron probes were used to analyze the microstructure of the cladding layer.Vickers hardness tester was used to detect the microhardness distribution of the cross-section of the cladding layer.At last,the wear resistance of cladding coatings and matrix was tested on a CFT-I multifunction material surface performance tester.Laser cladding technology was used to prepare Ti₃Al-based composite coatings on the surface of titanium alloy.The experimental results show that Ti₃Al,TiB,TiB₂,and TiN were in-situ generated by the laser-induced mixing of Ti,Al,and BN.In-situ synthesized fine needle-like Ti B,bulk or rod-like TiB₂ and dendritic Ti N are uniformly distributed on the gray-black Ti₃Al matrix;the more in-situ synthesized ceramic hard phase,with the increase of BN addition amount,the higher the hardness and wear resistance of the composite coating.The hardness and wear resistance of the 8 wt%BN coating were the best,and the maximum hardness of the surface layer of the cladding layer was 996 HV,which was about 3 times that of the matrix,and the wear resistance was about 7 times that of the matrix.In order to improve the quality of composite coating and eliminate pore defects,CeO₂ with different mass fractions was added to the composite coating.The experimental results show that the addition of CeO₂ makes the dispersed CeO₂ white particles appear in the microstructure of the cladding layer.The addition of appropriate amount of CeO₂ refines the grains and makes the structure more uniform,and plays a role of grain refinement and dispersion strengthening.When the content of CeO₂ is 2 wt%,the surface of the coating is free from pore cracks and the microstructure is fine and uniform.The microhardness is distributed steadily in the coating and reaches a maximum of 938 HV,which is about 2.7 times the hardness of the substrate.The wear resistance is about 8.8 times that of the substrate,about 1.7 times that of the CeO₂-free coating.Adding too much or too little CeO₂ will reduce the coating quality,so the amount of CeO₂added should be appropriate.In order to further improve the properties of the composite coating,the laser remelting treatment was performed on the prepared composite coating.The experimental results show that the laser remelting treatment can improve the flatness of the coating,relieve thermal stress,and eliminate holes and cracks and other defects under an appropriate remelting process.The microstructure of the composite coating after the laser remelting treatment becomes more uniform and dense,and the crystal grains are refined.The highest hardness of the coating after laser remelting is 851.3 HV,slightly higher than the hardness of the cladding layer,2.5 times that of the titanium alloy matrix;the wear resistance is about.2 times that of the laser cladding layer,about 3.7 times of the titanium alloy matrix.