Effects of Different Heat Treatment Processes on Dynamic Load Properties and Anisotropy of TC4 Titanium Alloy by Selective Laser Melting
The TC4 samples formed by selective laser melting(SLM)have poor fracture toughness,low cycle fatigue performance and obvious anisotropy.The TC4 samples were treated by the combination of cyclic annealing(at 700-950℃ respectively)and solid solution aging.The effects of heat treatment on the microstructure and mechanical properties of the TC4 samples were studied by optical microscope,scanning electron microscope and low cycle fatigue testing machine.The microstructure of SLM TC4 sample is composed of martensite α′ and martensite α″,the average value of fracture toughness is 36.4 MPa·m0.5,and the anisotropy of fracture toughness is 25.7%.After heat treatment,α lath is separated from each other,equiaxed α phase and secondary α phase are formed.The fracture toughness of SLM TC4 is 96.0 MPa·m0.5 after cyclic annealing at 700-950℃ and aging at 550℃,and the anisotropy of fracture toughness is 1.4%.Compared with the forged samples,the heat treated SLM sample exhibits better low cycle fatigue performance when the strain amplitude is greater than or equal to 0.9%;When the strain amplitude is less than 1%,the low cycle fatigue performance of the SLM sample produced by cyclic annealing at 920℃ and solid solution aging at 550℃ is higher than that produced by cyclic annealing at 920℃.
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