| With the development of national defense,aerospace and other fields,the demand for highstrength titanium alloy is increasing.?-type titanium alloy has excellent hardenability and workability,and if can obtain good matching of strength and plasticity through appropriate processing and heat treatment,so it is the best type of high strength titanium alloy for research.With the purpose of developing a new high-strength ?-type titanium alloy,this paper designed three kinds of ?-type titanium alloys based on the low cost alloying and d-electron alloy design theory including 2#:Ti-3Al-3.5Fe-6Mo-5Cr,3#:Ti-5Al-1.5Fe-6Mo-6Cr,4#:Ti-5Al-3.5Fe-7Mo-4Cr.Direct aging heat treatment,solid solution + aging heat treatment and solid solution + aging + annealing heat treatment were carried out on the three kinds of titanium alloys,respectively.The change were studied regulation of their microstructures and mechanical properties under different heat treatment conditions.The research results showed that:(1)after direct aging treatment of the three titanium alloys under the same conditions,their microstructure is composed of secondary ? precipitated phase and residual ? phase.With the increase of aging temperature,the volume fraction of the secondary ?phase decreases gradually,and the size of ? phase begins to grow thicker,and the secondary ? phase laminar distance becomes larger,leading to the decline of strengthening effect.Among them,the mechanical properties of 3# titanium alloy reached the best at 480?/8h aging condition,with the tensile strength of 1116 MPa and the elongation of 3.33%.(2)Three kinds of titanium alloys were treated with solid solution and aging at ?+? two-phase region and ? single-phase region,respectively.After solid solution at two-phase region,the strength of the samples is higher than that after solid solution in single-phase region.4# titanium alloy obtained the best properties at820?/0.5h+440?/8h of heat treatment,with the tensile strength of 1257 MPa and elongation of4.0%.(3)After solid solution + aging + annealing of the three titanium alloys,the volume fraction of the secondary ? phase is larger and the size is finer,compared with samples treated with solid solution+ aging.Compared with solid solution treatment in single-phase region and two-phase region,under this condition,it is easier to form multi-dimensional layered structure,which plays a significant strengthening effect on ?-type titanium alloy.At 750?/0.5h+480?/8h+650?/1h of heat treatment,the tensile strength of titanium alloy 2# can reach 1281 MPa and the elongation is 3.75%.Observation of the microstructure of several groups of titanium alloy samples with the best performance under different heat treatment conditions,the triangular structure of the secondary ?phase significantly improves the mechanical properties of titanium alloy.This structure limits the dislocation slip distance on the ? matrix,which is one of the reasons leading to the high strength of the alloys.In addition,the higher volume fraction of secondary ? and its finer size also contribute to the high strength of titanium alloys. |
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