Process And Property Control Of Selective Laser Melting Additive Manufacturing Of Titanium Alloy

As one of the most mature metal materials used in the selective laser melting technology?SLM?,the“customized”application of SLMed titanium alloy parts is always highly concerned by researchers,and the process and property control are the key of industrial application of SLMed titanium alloy parts.In this paper,the Ti6Al4V powder was selected to fabricate the SLMed Ti6Al4V specimens.The influence of process parameters on the forming quality and microstructure of the SLMed Ti6Al4V specimens were investigated and finally the precise control of the mechanical and electrochemical corrosion properties was achieved.The main research results are as follows:SLM process was applied to prepare the Ti6Al4V alloy in bulk-form with different laser process parameters.With the increase of laser power and decrease of scan speed,the densification level increased and the highest density of SLMed part could be up to 99%.There were?columnar crystals which pass through a plurality of powder layer thicknesses on the side surface of the SLMed Ti6Al4V specimens and the martensite?'was the main constituent phase in SLMed Ti6Al4V specimens.Through the change of process parameters,the dimensional accuracy of the SLMed Ti6Al4V parts could be controlled.When the laser power was 225 W and the scan speed was 600 mm/s,a high tensile strength?1103.16 MPa?and a comparably low elongation?4.09%?were obtained.Based on the optimization of laser process parameters,the Ti6Al4V alloy specimens with different building orientations were fabricated.The densification level of the SLMed Ti6Al4V specimens fabricated at XZ-orientation was apparently higher than that obtained at XY-orientation.While fine martensite?'was obtained in the as-fabricated samples,acicular shaped martensite was observed at XY-orientation and the lath-shaped martensite tended to be formed at the XZ-orientation,which was due to the heat accumulation effect in different forming directions.The difference in heat accumulation caused by different forming directions led to the difference in densification behavior and microstructure evolution of the formed specimens.When the laser power P=175 W and the forming direction was XZ-orientation,the tensile strength of the formed SLMed Ti6Al4V plate was up to 1021.45 MPa and the elongation was 3.97%.The electrochemical corrosion property of NaCl solution was tested for different cross sections of SLMed Ti6Al4V specimens under different process parameters.It was found that the corrosion rate of Ti6Al4V specimens fabricated by SLM in 3.5%NaCl solution was slower and the corrosion resistance was better.As the scan speed increased,the degree of densification of the SLMed specimens gradually decreased,resulting in a gradual decrease in the corrosion resistance of the SLMed specimens.The corrosion resistance of the bottom surface was much better than that of the side surface of the SLMed Ti6Al4V specimens.After corroding in NaCl solution,the passive film on the surface of the SLMed Ti6Al4V specimens was mainly composed of two oxides of TiO₂ and Al₂O₃.On the corrosion morphology,a pitting corrosion occurred in the micro-pores of the formed specimens and there was a significant enrichment of O elements in the micropores.