| Metastable ?-type titanium alloys have shown a wide range of application prospects in aerospace,ocean exploration and biomedical fields because of the structural and functional properties,such as high specific strength,excellent corrosion resistance and favourable biocompatibility.Furthermore,these alloys exhibits the diversity of deformation modes during the tensile process,such as,stress-induced ?? martensite and ? phase transformation,{332}<113> and {112}<111> twinning and dislocation slip.The previous researches on tensile properties of To-Mo-Fe alloys plates at room temperature showed that the alloys deformed by {332}<113> twinning and dislocation slip,among which the {332}<113> twinning made the alloys a good strength and plasticity matching.The number of twins decreased with the increase of Fe contents,and consequently,the strength was increased and the ductility was decreased.However,the influence of {332}<113> twinning on fatigue performance remains unclear.The microstructure and fracture morphology of Ti-10Mo-x Fe(x=1,2,3)alloys were systematically investigated by means of optical microscope and scanning electron microscopy in this paper.The tensile test and strain-controlled symmetric tensile-compression low cycle fatigue tests with total strain amplitudes of 0.5%,1.0% and 1.5% were carried out by the Shimadzu 4830 electro-hydraulic test machine,the tensile and low cycle fatigue mechanical properties of Ti-10Mo-xFe alloys with different deformation modes were investigated.Meanwhile,the research investigated the microstructure evaluation at low cycle fatigue fracture of Ti-10Mo-xFe(x=1,2,3)alloys,and analyzed the fatigue fracture morphology of the alloys.Finally,the effects of different plastic deformation modes on the low cycle fatigue properties of the alloys were discussed.The experimental results showed that the yield strength and tensile strength of Ti-10Mo-xFe alloys under the condition of tensile tests at room temperature were increased from 698 MPa to 812 MPa and 888 MPa and 952 MPa,respectively.However,the total elongation rate was decreased from 38% to 16%,and the work hardening rate was decreased gradually.In addition,the plastic deformation modes of the alloys were transformed from {332}<113> twinning to dislocation slip.The low cycle fatigue life of the Ti-10Mo-xFe alloys was negatively correlated with Fe contents and strain amplitudes.What's more,the initial cyclic hardening occurred in Ti-10Mo-xFe alloys,and the cycle stability phase accounted for more than 90% of the total fatigue life.The Ti-10Mo-xFe alloys exhibited the ductile fracture,and the fracture was composed of three parts: fatigue source region,crack propagation region,and final rupture region.The width of fatigue striation increased gradually with the increase of Fe contents.And for the same alloy,the total proportion of fatigue source region and crack propagation region increased with the increase of strain amplitude.The Ti-10Mo-1Fe alloy and Ti-10Mo-2Fe alloy were mainly deformed by {332}<113> twinning,while Ti-10Mo-3Fe alloy was mainly deformed by dislocation slip during the low cycle fatigue test.The {332}<113> twins formed in Ti-10Mo-1Fe alloy during the tensile-compression process induced significant plastic deformation ability,simultaneously,The generation of a large number of twins induced the dynamic Hall-Petch effect,and effectively released the local stress concentration and delayed the initiation of fatigue cracks.The aforementioned reasons resulted in the excellent ability of low cycle fatigue in Ti-10Mo-1Fe alloys with twinning induced plastic deformation effect. |
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