Research Of The Process Parameters Optimization And Properties For Laser Cladding Ti-Al Based Coatings On Titanium Alloy

Titanium alloy is widely used in aerospace,petrochemical,biomedical and other fields owing to its excellent properties such as low density,high specific strength,good corrosion resistance,etc.However,titanium alloy has low hardness and poor wear resistance,which restrict its further application.To improve the properties of titanium alloy,the Ti-Al-based composite coatings were prepared on the surface of TC18 by laser cladding technology.The powder of Ti,Al and Si₃N₄ were used as cladding materials in this paper.The influence of process parameters,Ti-Al atomic ratio and Si₃N₄ content on the microstructure and mechanical properties of the coatings were observed by XRD,SEM,EDS,EPMA,microhardness testing,friction and wear testing,etc.The optimal experimental results were obtained after comparison.Different process parameters were used to prepare coatings with same Ti-Al atomic ratio.It is observed that the macroscopic morphology of the coating,the degree of fining grain of TiAl phase,and the mechanical properties are affected by laser power and scanning speed.The coating with laser power at 1100-1300 W and scanning speed at 4-5 mm/s has the best performance,which average hardness is 550 HV,about 1.8 times of the substrate,and the wear resistance is about 3.4 times of the substrate.Coatings about different Ti-Al atomic ratio were prepared by the optimum process parameters.It is observed that with the increase of Al element ratio,the metallic luster of the coating decreased.The microstructure of the coatings change from basket-weave Ti₃Al phase,to lath Ti₃Al phase,next dendrite TiAl phase,then equiaxed TiAl₃ phase.No obvious microstructure is observed at 1:2 Ti-Al atomic ratio.,The microhardness of the coating decrease with the increase of Al content,and the wear resistance turn increase to decrease.The highest average hardness of coating which Ti-Al atomic ratio is 3:1,630 HV,about 1.9 times of the substrate.The best wear resistance of coating which Ti-Al atomic ratio is 1:1,about 3.4 times of the substrate.The Ti-Al atomic ratio of 1:1 coating has the best comprehensive performance.The Si₃N₄ particles were added in Ti-Al coatings with the best atomic ratio by the optimum process parameters.It is found that new phases TiN and Ti₅Si₃ appeared in the coating.With the increase of Si₃N₄ content,the width and height of the coatings decrease,the depth of bath and dilution rate increase.The microstructure delamination is observed in the coating.Eutectic structure of Ti₃Al/Ti₅Si₃ and particles or bar structure of TiN are existed at the bottom of the coating,lamellar structure of Ti₅Si_3,TiN particles and acicular structure of TiAl_xN_y are observed at the top of the coating.The highest average hardness of the coating is 910 HV,about3.0 times of the substrate,which contains 15 wt%Si₃N₄.The best wear resistance of the coating which contains 10 wt%Si₃N₄,about 4.8 times of the substrate.The coating which contains 10wt%Si₃N₄ has the best comprehensive properties.