Study On Effects Of Electropulsing Treatment On Microstructure And Mechanical Properties Of Laser Melting Deposited Ti6Al4V Alloy

In order to further optimize the mechanical properties of laser melting deposited Ti6Al4 V alloy,the ultrasonic impact treatment was introduced into laser melting deposition.After deposition,the post-electropulsing treatment was applied.In the present work,the microstructure and mechanical properties of Ti6Al4 V alloy prepared by different processing were systematically investigated by means of X-ray diffraction(XRD),optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM)observation,industrial CT analysis(ICT),electron backscatter diffraction(EBSD)analysis,tensile and microhardness testing.The influencing mechanisms of ultrasonic impact and electropulsing on microstructure and mechanical properties were analyzed.The results show that the lack of fusion defects in Ti6Al4 V alloy could be effectively eliminated by introducing ultrasonic impact treatment.After application of ultrasonic impact treatment,the microstructure of Ti6Al4 V alloy changed from the basket-weave morphology to martensite.With increasing laser power or decreasing laser scanning speed,the content of martensite gradually increased.The martensite is characterized by a large distortion,convex morphology,internal dislocation and the same crystallographic orientation in a primary β phase grain.The sample prepared by laser melting deposition and ultrasonic impact treatment shows large yield strength and small elongation because of the existence of martensite.The fracture surface morphology indicates that the fracture behavior is mainly determined by intergranular fracture.In the present work,post-electropulsing treatment was used to anneal Ti6Al4 V alloy prepared by laser melting deposition.The results show that when the voltage increases from 0V to 130 V,the microstructure changed in the order of martensite→colony α lath→basket weave.The aspect ratio of α lath was reduced and the preferred orientation of α phase caused by large thermal gradient was weakened.The anisotropy in yield strength was obviously reduced,which was attributed to the almost equivalent distribution of Schmid factor in the samples deformed along different orientations.For the sample prepared by laser melting deposition and ultrasonic impact,the postelectropulsing can also promote the formation of basket-weave structure and improve the elongation of Ti6Al4 V alloy.When the laser power was 1800 W and the laser scanning speed was 300 mm/min,for the sample prepared by laser melting deposition and ultrasonic impact treatment,its yield strength and elongation could reach 993±39 MPa and 6.5±0.9 %,respectively,after electropulsing treatment.The above results indicate that the mechanical behavior of Ti6Al4 V alloy can be tailored by controlling the processing parameters of laser melting deposition,ultrasonic impact and electropulsing treatment...