Simulation Of Electron Beam Selective Melting Forming And Thermal Interaction Based On TC4

TC4 alloys exhibit low density,high specific strength,high plasticity,high fatigue,excellent corrosion resistance and biocompatibility,are widely used in aerospace,marine vessels and bio-medical fields.The requirements of the integration of parts,lightweight,and structural integration are increasing in aerospace,marine and biomedical fields.Traditional manufacturing technology can not longer meet these requirements.Electron beam selective melting（Selective Electron beam melting,EBSM）is of high energy utilization,fast processing speed,and vacuum protection,considered as an ideal technology to manufacture high-performance,integrated TC4 alloys.However,it is not possible to accurately grasp the temperature variation during EBSM under the current experimental conditions,resulting in heterogeneous micro-structure and unstable mechanical properties.Therefore,it is necessary to further investigate the thermal interaction process of TC4 manufactured by EBSM.This paper simulates the thermal interaction process,and analyzes the influences of different process parameters on thermal cycle,cooling rate,molten pool range and re-melting area,obtaining the optimum ranges of technology parameters.And then,the forming size,density,microstructure and mechanical properties were analyzed,obtaining the best process parameters to guide the actual manufacturing.The effects of overlap rate are investigated by simulations during EBSM.The results showed that low lap rate（<50%）is insufficient to completely melt the powder.High overlap rate（>70%）causes more remelting between in two adjacent passes and larger molten pool,resulting in stress concentration and corresponding cracks and porosity.When the overlap rate is about 60%,the better forming quality is obtained due to reasonable energy input and cooling rate for annealing during temperature rise.As the the number of layers increases,the re-melting area increases,resulting in increasing of the matrix temperature.The needle-likeαmartensite transforms into the coarse network structure through slowly absorbing energy.The effects of the residence time are also investigated.The results show that the maximum cooling rate increases from 3.25×10⁴℃/s to 1.26×10⁵℃/s with the increase of the interlayer residence time;the variation of peak value for cooling rate decreases.The optimal interlayer residence time is 1s～2.5s.The experimental results of the TC4 alloys fabricated by EBSM show that the grain size of the columnarβphase with coarse grains and poor continuity was about 200μm at the overlap rate of 50%;the grain size was about 150μm at the overlap rate of 60%,the grain size was about 300μm and holes appear.The forming accuracy error in each direction is:F_Z>F_X>F_Y.The overal accuracy errors at different overlap rates are:A_60%>A_50%>A_70%;the higher microhardness is 417.3HV_0.2and the lowest roughness is 0.7μm at the overlap rate of60%.The higher density is 99.41%at the overlap rate of 70%。...