Investigation On Process And Performance Of TC4 Alloy Fabricated By Selective Laser Melting

With the advantages of low density,high specific strength,good heat resistance and excellent corrosion resistance,TC4 alloy has been widely used in aerospace,marine,energy and chemical industry,biomedical and other fields.With the increasing demand for lightweight,integral,structural and functional integration in modern industry,the parts also show the trend of higher integration level and more complex structure,and the traditional manufacturing technology cannot meet the manufacturing needs of the current part.The selective laser melting technology adopts discrete superposition machining method,which can directly form parts with complex structure and excellent performance.It is the best method to solve the machining problem of complex titanium alloy components.In this paper,the influence of process parameters on microstructure and properties of selective pulsed laser melting samples was studied with TC4 titanium alloy powder as raw material,and the effect of annealing temperature on microstructure and properties of selective pulsed laser melting specimens was also discussed.The main research contents and conclusions are as follows:(1)The influence of selective laser melting process parameters on the internal density of TC4 alloy was studied.The optimum parameters of selective pulsed laser melting of TC4 alloy powder were obtained.The results show that the influence of hatching space parameters on the density of formed samples is great.Under the condition of insufficient energy input,the forming quality decreases linearly with the increase of hatching space,and in the case of sufficient energy input,the hatching space mainly affects the porosity of the cross-section of the sample.In the selective laser melting process,the inner density of the sample is mainly caused by large size spheroidization,unfused and small size spheroidizing defects,etc.The optimum parameters obtained by orthogonal experiment are as follows: laser power 280 W,scanning point distance 90?m,exposure time 70?s,hatching space 0.07 mm,layer thickness 40?m.(2)The influence of hatching space parameters,which is the most influential process parameter,on the microstructure and properties of TC4 alloy samples formed by selective laser melting technique was studied.The results illustrate that with the increase of hatching space parameters,the energy density per unit area decreases,the content of decomposed martensite decreases and the dispersion strengthening effect weakens gradually.With the increase of hatching space parameters,the microhardness and yield strength of TC4 alloy samples decrease,and the elongation of the samples increases first and secondarily decreases.The anomalous decrease of elongation after hatching space(0.11mm)is due to the significant increase of internal porosity.(3)The effect of annealing temperature on the microstructure and properties of TC4 alloy samples formed by selective laser melting technique was studied.The results illustrate that the ?' phase martensite in the microstructure of TC4 alloy decomposes gradually after annealing heat treatment.With the increase of annealing temperature,the content of martensite ?' phase in microstructure decreases gradually,and the content and size of ? and ? phases increase gradually.When the annealing temperature reaches 800?,the ?' phase of martensite completely disappears and becomes the mixed structure of Weimite and basket,and when the annealing temperature continues to rise to 900?,the microstructure is completely transformed into reticulated structure.With the increase of annealing temperature,the strength and hardness of TC4 alloy decreased and the elongation increased.