Study On The Technological Properties Of TAL5 Titanium Alloy By Selective Laser Melting

TA15(Ti-6.5Al-2Zr-1Mo-1V)titanium alloy belongs to near-?type titanium alloy.It not only has good thermal strength and weldability of?type titanium alloy,but also has technological plasticity close to that of?-?type titanium alloy.It also has medium room temperature and high temperature strength,low density and corrosion resistance,which are widely used in aerospace components and engine structures.For the manufacture of TA15 titanium alloy aircraft structural parts with complex shape and structure,the traditional forging method has some shortcomings,such as high equipment requirement,complex technology,low material utilization and long production cycle.Selective laser melting(SLM),as the most promising manufacturing method,provides the possibility for processing TA15 parts with low cost,short production cycle and complex shape.Therefore,it is of great significance to study the technological properties of TA15 alloy formed by SLM.In this paper,TA15 alloy powder is used as raw material,and selective laser melting forming technology is used as processing method.The influence of laser parameters on the internal defects and cracks of samples is studied.The formation mechanism of pores and cracks is analyzed.The morphological microstructures are studied and the formation process of the microstructures is clarified.The influence of laser energy density on microstructures and mechanical properties was studied,and the relationship between laser energy input,microstructure and mechanical properties was clarified.Finally,by studying the effect of heat treatment on the microstructures and mechanical properties,the heat treatment samples with uniform structure,good matching of strength and elongation,and mechanical properties exceeding the forging standard were obtained.The results show that the scanning spacing has an important influence on the upper surface morphology in SLM process parameters.The energy input of laser affects the type and number of internal defects.With the increase of laser energy density,the non-fused void defect transits to spherical pores defect.The density increases first and then decreases,and the relative density reaches 99.7%.The reason of cracking under high energy input is that there is a large thermal stress inside.,which acts on the sharp corner of the side wall to form a stress concentration.Needle martensite have poor internal crack resistance.Spherical particles solidified by spattering metal droplets have poor bonding with the matrix.These factors together lead to transverse cracking and propagation of the specimen.The internal structure of SLM forming is composed of acicular?'martensite.Five thermal cycles with different peak temperatures during deposition result in the grading of acicular martensite.With the increase of laser energy density,the tensile strength and elongation of the formed specimens decrease gradually,while the yield strength increases gradually.When the laser energy density is 52.91 J/mm~3,the tensile strength reaches 1250 MPa,the yield strength reaches 1063 MPa and the elongation reaches 3.1%.Basket structure consisting of?+?phase was obtained after heat treatment at 750?,840?,900?and940?.With the increase of heat treatment temperature,the tensile strength and yield strength decrease gradually,and the elongation increases gradually.The fracture mechanism changes from semi-ductile and semi-cleavage fracture to ductile transgranular fracture.After heat treatment at 940 C,The elongation increases to 11.5%,the tensile strength is 1061 MPa and the yield strength is 961 MPa.After heat treatment at 900?and 940?,the tensile properties exceed the annealed forgings standard.The relationship between process parameters/heat treatment microstructures mechanical properties of TA15 alloy formed by selective laser melting has been established,which provides a reference for further research on SLM process of TA15alloy.