Study On The Defect Control Of TA15 Formed By Selective Electron Beam Melting

TA15 titanium alloy belongs to ? series alloy,which has the characteristics of high specific strength,creep resistance,corrosion resistance,good welding performance and shows broad application prospect due to its good performance.However,due to the complexity of TA15 structural parts in the aerospace field,it is generally difficult to be processed by traditional cutting methods,which restricts its development.Selective electron beam melting(SEBM)is a popular additive manufacturing technique in recent years,which can produce parts with complex structures.It is of great significance to combine SEBM technology with TA15 structure.In this paper,the mechanism of TA15 selective electron beam melting and defect control are studied:Firstly,the physical model of molten pool in SEBM was constructed;Based on the Gaussian body heat source model theory,the temperature field in the molten pool under electron beam was analyzed;The internal force field distribution of molten pool was analyzed by combining surface tension,Marangoni force and steam recoil pressure.On this basis,the influence of forming process on the thermal distribution of the internal force of the molten pool was analyzed,which provided a theoretical basis for the following research on defect control.Secondly,the type of phase,microstructure and phase transformation process of TA15 electron beam selective melting parts were analyzed by orthogonal experiment with three factors and four levels;The tensile fracture morphology and fracture mechanism of the formed sample were discussed based on the tensile experimental;The fractal dimension and root mean square deviation are introduced to characterize the fracture morphology,and the evolution rules between the fracture morphology,the tensile strength and the percentage of section shrinkage were analyzed.Then the internal relationship among the tensile properties-fracture morphology-microstructure was established,which provides support for the study of SEBM defect control of titanium alloy.Based on the above investigation,the formation mechanism of machining defects such as the surface ladder,surface spheroidization,internal micropore and internal unmelted powder was analyzed.The triangular cross-section error method and numerical image processing method were used to quantitatively characterize these formation mechanisms of machining defects.Finally,the effects of molding parameters on surface spheroidization,internal micropores and internal unmelted powders were investigated.The relationship between forming parameters,tensile strength and the percentage of section shrinkage was obtained by range analysis method,and the forming process parameters with optimal performance were obtained at last.