| With the rapid development of aerospace technology,higher requirements for the geometry and mechanical performance of key structure components are put forward to meet the increasingly harsh service environment.Selective Laser Melting(SLM)technology is a promising additive manufacturing technology,which has a great potential in the integral forming of complex structural parts based on the computer-aided design and the layerwise stacking method.Due to the extremely high cooling rate in the SLM process,fine microstructure is formed in the SLM-fabricated parts,which results in the better mechanical properties,compared with the counterparts fabricated by casting standards.As a kind of near-alpha titanium alloy,Ti-6Al-2Zr-1Mo-1V(TA15)alloy combines the outstanding thermal strength and weldability of?titanium alloy and good plasticity of?+?titanium alloy.It is widely used in the aerospace industry owing to its ability to work at high temperature of500°C for a long time.Based on such problems,the influence of SLM process parameters on the microstructure and mechanical properties was investigated for process optimization.Moreover,the heat treatment was conducted to tailor the microstructure and mechanical properties.In addition,different powder forming technologies were carried out to compare the effect of manufacturing method on the microstructure and mechanical properties of TA15alloy.The main research work and achievements are as follows:The process parameters of SLM forming TA15 alloy were explored,and the effect of different laser power on the microstructure and properties of the parts were studied.The results show that the microstructure is composed of acicular?'martensite.As the laser power increases,a small amount of pores appear,as a result,the mechanical property gradually decreases.The optimized process parameters are:laser power of 230 W,scanning speed of675 mm/s,and layer thickness of 0.03 mm.The tensile strength and elongation of TA15 part at room temperature are 1422.07 MPa and 9.5%,respectively.Besides,the tensile strength at500°C is 990.2 MPa and the elongation is 15.6%.The effects of different heat treatment temperatures on the phase composition,microstructure and mechanical properties of SLM-fabricated TA15 alloy were investigated.After heat treatment at 650 ~oC,750 ~oC,850 ~oC,950 ~oC,1000 ~oC and 1100 ~oC,the needle-like?'martensite in the as-SLMed deposition sample transforms into lath-like?and?phases,and the grain size gradually increases.With the increase of heat treatment temperature,the tensile strength at room temperature and high temperature(500 ~oC)decreases gradually,while the elongation at room temperature increases first and then decreases,peaking at 750~oC.In the high temperature tensile test at 500 ~oC,the elongation increases gradually,and decreases slightly when the temperature reached 1100 ~oC.Combined with the tensile properties at room temperature and high temperature of 500 ~oC,the optimal heat treatment process is as follows:holding at 750 ~oC for two hours and cooling with furnace.The elongation of samples at room temperature and 500 ~oC is 55%and 13.6%higher than that of as-SLMed samples,respectively.Other powder forming technologies including SPS,HIP and Casting were also utilized to fabricate TA15 alloy.The results show that the SLM-fabricated TA15 samples consiste of acicular?'martensite,while the TA15 samples manufactured via SPS,HIP and Casting technology formed mainly consist of coarse lath-like?phase and?phase.And the grains are more than ten times larger than those of SLM-fabricated samples.The room temperature tensile strength of samples made by SLM is about 48.2%,67.9%and 53.6%higher than that of SPS,HIP and Casting samples respectively.Meanwhile,the elongation of the SLM-fabricated samples is also relative better.Additionally,it also has a excellent combination of strength and plasticity near its service temperature,with tensile strength at500 ~oC 75.3%,84.4%and 51.8%higher than that of SPS,HIP and Casting samples,respectively. |
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