Research On Preparation And Simulation Of Ti-Al Laser Cladded Coating Reinforced By Nano Powder On TC4 Titanium Alloy

This paper presented a scientific basic research on preparation and simulation of Ti-Al Laser cladded coating reinforced by nano powder on TC4 Titanium alloy, mainly including the dispersion of nano Y₂O₃ particles, simulation of laser cladding process, preparation of nano particle reinforced TiAl composite coatings, optimization of laser cladding process parameters and analysis of microstructure and performance of the coatings.The major work and corresponding results are described as follows.（1） Through three sets of single factor experiments, the effect of dispersion medium, theoretical mass fraction of particles and dispersion time on ultrasonic dispersion was analyzed and the corresponding process parameters were optimized. Through a set of orthogonal experiments, the effect of milling speed, milling media to material ratio and milling time on ball milling dispersion was analyzed and the corresponding process parameters were optimized. The dispersion behaviors of nano Y₂O₃ particles under different dispersion methods were studied and the optimized dispersion method was obtained as ball milling/ ultrasonic dispersion.（2） Through a set of orthogonal experiments, the process parameters of cladding 50at%Ti-50at%Al composite powder on TC4 were optimized. Based on the result of the orthogonal experiments, the process parameters of preparing nano TiC-Y₂O₃ reinforced Ti-Al composite coating were optimized through single factor experiments. The optimized composite cladding coatings can be obtained with the laser power of 700 W, spot diameter of 1mm and scanning speed of 200mm·min-1.（3） A three dimensional finite element model was established to simulate temperature field in the process of preparing Ti-Al composite coatings using laser cladding. Through the simulations, the effect of laser power, scanning speed and spot diameter on the molten pool size, highest temperature, temperature gradient, cooling rate and shape control factor was studied. A set of optimized process parameters were achieved based on single factor simulation experiments. The significances of different parameters were obtained based on orthogonal simulation experiments. The limits of using laser specific energy to represent laser parameters were discussed.（4） The microstructure and microhardness of 10 different Ti-Al composite laser cladding coatings were obtained by SEM, EDS, XRD and microhardness tester. The results show that the composite coatings consist of large amount of Ti3 Al, TiAl, TiAl3 and small amount of Y₂O₃ and TiC. The microhardness of all the prepared composite coatings is substantially improved compared with TC4 substrate. Nano TiC particlaes play an important role in microhardness enhancement and nano Y₂O₃ particles improve the uniformity of microhardness distribution and increase its depth range.