Process Study Of Graphene Oxide Reinforced Titanium Matrix Composites Manufactured By Selective Laser Melting

Titanium alloy has become the preferred material for key components in aerospace,petrochemical,biomedical and weapon equipment fields owing to its outstanding performaces,such as low density,high specific strength,excellent bio-compatibility and corrosion resistance.Nevertheless,the low elastic modulus,non-wear resistance and poor heat transfer ability of titanium alloy limit its further development in the field of aerospace and national defense equipment.Laser additive manufacturing technology has the characteristics of fast forming speed,high processing flexibility,high material utilization rate and multi-phase material designability,which makes it show unique advantages in preparing metal matrix composites.Hence,in this work,graphene oxide(GO)served as a reinforcement phase was utilized to improve the wear resistance of TC4 substrate,and the titanium matrix composites were manufactured by selective laser melting technology(SLM).This study investigates the effects of process parameters on the forming quality and properties of GO/TC4 composites by the comibination of numerical simulation and experimental methods,and the in-situ strengthening mechanism of GO was revealed.Combined with multi-objective genetic algorithm,the optimal forming process parameters of GO/TC4 composites were explored.The main research contents are as follows:(1)Analysis of temperature field and stress field of GO/TC4 composites during SLM process.Based on the laser Gaussian heat source model,temperature field and stress field theory,the numerial simulation model of GO/TC4 nanocomposites during SLM process was established.The effects of scanning strategies(linear scanning,strip scanning,hollow-square scanning and check-board scanning)on the temperature distribution and stress evolution during the SLM process of GO/TC4 composites were investigated utilizing the ANSYS 19.0 software,and the optimal scanning strategy was explored.The results show that when the GO/TC4composites were fabricated by the divisional chess-board scanning strategy,it is beneficial for the genearated heat to transfer to the surroundings,meanwhile the heat effect is the least.Moreover,the distribution of equivalent stress in the sample is relatively uniform,resulting in the least thermal stress.(2)Study on the influence of laser process parameters on the forming qualities of GO/TC4 composites.Based on the single factor method,the influence of laser power and scanning speed on the forming qualities of GO/TC4 composites were analyzed with the comibination of the surface morphology,microhardness and tribological properties,leading to a prefeered range of laser process parameters.In addition,the influence mechanism of laser process parameters on the forming qualities of GO/TC4 composites was revealed.The results show that with the increasing laser power and scanning speed,the microhardness and wear resistance of GO/TC4 composites show a trend of first increasing and then decreasing.When the laser power and scanning speed is selected as 160W and 1000mm/s,GO/TC4 composites prepared by SLM perform the best forming qualities.(3)Study on microstructure and properties of GO/TC4 composites and strengthening mechanism of GO.GO/TC4 composites with different mass fractions were fabricated on the basis of the optimized range of laser process parameters.The surface morphology,microhardness and wear tests were performed to investigate the effects of GO content on the forming qualities of GO/TC4 composites,and the in-situ formation mechanism of GO/TC4composites under high energy laser was further revealed combined with the analysis of the microstructure and phase composition.The results show that the addition of GO reduces the self-bonding of TC4 matrix,leading to a decrement in surface density with the increase of GO content.When GO content is 1.0wt.%,the microhardness is the highest with the value of441.4HV_0.2.When the content of GO is 0.5wt.%,the sample perform the best wear resistance,resulting from the in-situ formation of Ti C?Ti O₂ and Al₂O₃ phase,meanwhile the wear loss is reduced to 4.01×10^-2mm³,which reveals the strengthening effect of GO on TC4 matrix under the action of laser.(4)Study on process optimization of GO/TC4 composites manufactured by SLM process.Based on response surface regression test,the predical model of forming qualities of GO/TC4composites was established,and the interactive influence of laser process parameters and GO content on the forming qualities of titanium matrix composites was analyzed.Based on multi-objective genetic algorithm,the forming process parameters of GO/TC4 composites were optimized,selecting microhardness,compactness and wear resistance as the purpose.Finally,the Pareto solution set of the process parameters of GO/TC4 composites fabricated by SLM process was obtained.On this basis,the optimized process parameter combination was verified by experiments,and the reliability of the optimization model was determined.