| Titanium and titanium alloys have various excellent properties:low density,high specific strength and modulus,high corrosion resistance,excellent high and low temperature steength,non-magnetic,no toxicity and good biocompatibility,which make them important structural materials.The typical titanium alloy is TC4(Ti-6Al-4V(wt.%)).However,the applications of titanium and titanium alloys are largely limited by their higher production costs.In this paper,titanium hydride powder and aluminum-vanadium intermediate alloy particles were used as raw materials,and the low-cost and highperformance TC4 titanium alloy samples were successfully produced by the process including preparing powder by mechanical ball milling and mixing,compacting powder using molds and consolidation of powder blank by extrusion forging under an inert atmospheric protection.The microstructures and mechanical properties of TC4 titanium alloy samples were studied by means of optical microscopy,laser confocal microscopy,scanning electron microscopy,transmission electron microscopy,X-ray diffractometry and electronic universal testing machine.The main conclusions are as follow:1200℃ and 1300℃ were selected as the consolidation temperature,the holding time was 5 min.In the prepared extruded-forged PM-TC4 titanium alloy samples,the Al and V elements were uniformly distributed,the dehydrogenation efficiency was 97%,and the microstructure mainly included lamellar α phase,β phase and β transformation structure composed of ultrafine needle-like α’ phase.The average width of the a phase was 0.71 μm and 0.72 μm,respectively.The yield strength(YS)of the samples was 1100 and 1094 MPa respectively,and their ultimate tensile strength(UTS)was 1257 and 1227 MPa respectively.In terms of plasticity,the elongation to fracture of the sample consolidated at 1200℃ was 10.4%,and that of the sample consolidated at 1300℃ was clearly lower,being 7.4%.The fracture mode of the sample was different from the ductile fracture mode of traditional ingot metallurgical titanium alloy,and its mechanism was quasi-dissociation fracture mode;The PM-TC4 titanium alloy samples prepared by extrusion forging at 1200℃ and 1300℃ were vacuum annealed at 700℃ for 6 hours,and the microstructure and mechanical properties of the heat-treated samples were analyzed.The results showed that the dehydrogenation rate of the sample increased to 99.7%,which meant the dehydrogenation was complete.The microstructure consisted mainly of the lamellar a phase and the discontinuous β phase,in which the average width of the a phase was 0.70μm and 0.71 μm.The strength and plasticity of the sample were further improved after the vacuum annealing heat treatment,The YS of the samples obtained at 1200℃ and 1300℃ were 1122 and 1167 MPa respectively,their UTS was 1186 and 1230 MPa respectively,and their elongations to fracture was both 11.2%.The fracture mechanism of the sample was quasi-dissociation fracture mode.It was found that β-phase-rich regions existed in the micro structure of the sample fabricated using the same process,but by a powder blend prepared by another type of mixer.The YS,UTS and elongation to fracture of the sample were 1094 MPa,1282 MPa,and 4.1%,respectively.After annealing at 955℃,the width of the α phase in the sample increased,and the β-rich phase region became more obvious,which further reduced the mechanical properties of the sample.Its yield strength,tensile strength,and elongation were 984 MPa,1012 MPa,and 0.6%,respectively.This was because the heat treatment process increased the hardness difference between the a phase and the β phase,and the deformation between the two phases was more uncoordinated.The β-rich phase region that deformed first caused rapid concentration of strain,which made holes were generated in these area at lower flow stress,causing the sample to fracture after less macroscopic plastic deformation.The process selects titanium hydride instead of titanium as raw material,and combines the dehydrogenation,consolidation and forming process.In the process,there are the advantages of simple process and near-net shape,which not only reduces the production cost,but also ensures that the prepared titanium material has excellent mechanical properties. |
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