Study On Internal Defects And Mechanical Properties Of Titanium Alloys Formed By Selective Laser Melting

TC4 titanium alloy samples containing artificially designed defects were prepared by additive manufacturing forming technology of selective laser melting(SLM).The effect of defect detection methods and the size and location of embedded defects on the tensile properties of formed alloys at room temperature was studied.The results show that the film radiographic inspection accuracy is the same as that of computer radiographic inspection(CR).The film is not affected by the parameters,but the CR inspection is more affected by the parameters.The digital radiographic inspection(DR)inspection accuracy is higher than the two;From the CT testing results,it is found that in addition to the artificially implanted holes in the sample,there are also a large number of micron scale uncontrolled printing defects.Single hole defect When the diameter of embedded defect is less than a certain size,the tensile strength of the alloy basically remains unchanged,and the samples break from the non embedded defect area;When the diameter of the embedded defect exceeds this size,the tensile strength decreases significantly with the increase of the defect size.At the same time,the decrease of the edge hole sample is large,and the sample breaks from the embedded defect area.Based on Saint Venant’s principle and experimental results,a ratio of d/D(ratio of hole size to sample cross section)for TC4 titanium alloy samples prepared by SLM is 0.23,and the ratio of hole defect size to cross section size can roughly predict the hole fracture.Compared with the strength alloy,the elongation is more significantly affected by defects.With the increase of defect size,the elongation first shows a trend of gradually decreasing,when the sample is at the hole,it will be later.The defect size is the dominant factor affecting the strength and elongation of additive manufacturing alloy.The tensile strength of the alloy with porous holes is the same as that of the alloy with single hole.However,the elongation decreases inversely with the increase of the hole size.In conclusion,the TC4 titanium alloy samples prepared by SLM inevitably have internal defects.The tensile strength has a certain tolerance for hole defects,but to ensure plasticity,defects should be minimized.