Microstructure And Mechanical Properties Of Solid State Recycled TC4 Alloy

Titanium alloys are widely used in aerospace,marine engineering,biomedical and other fields,They have many advantages such as low density,high specific strength,good biocompatibility and so on.TC4(Ti-6Al-4V(wt.%))alloy is a ?+? titanium alloy,which is the most widely used titanium alloy.Its annual output accounts for about 70%of the total output of titanium alloys.With the increase use of titanium alloys,the amount of chips generated in the machining process is also increasing.The main problems currently limiting the application of titanium alloys are high cost and low utilization.In this study,Ti-6A-4V alloy machining chips were hydrogenated,in-situ dehydrogenated and thermomechanically consolidated to fabricate bulk Ti-6Al-4V alloy samples.The thermomechanical powder consolidation process used was powder compact extrusion-forging.The microstructure of the sample was characterized by optical microscopy,scanning electron microscopy and transmission electron microscopy.The mechanical properties such as strength and elongation to fracture of the extrusion forged sample were measured by universal tensile testing machine.The fracture surfaces and longitudinal sections near the future surfaces of the tensile test specimens were observed by scanning electron microscopy to clearify,the fracture mechanism of the sample and the consolidation level of the powder.The hardness and density of the samples were also measured.The results show that microstructure of the extrusion-forged Ti-6Al-4V alloy samples after consolidation is gradually transformed from ? phase into?-sheet structure along the original grain boundary and staggered martensite structure.As the consolidation temperature increases,the ?-lamellar structure and the acicular ?' from the martensitic transformation tend to grow.The extrusion-forged samples fabricated with different consolidation temperatures were characterized.It was found that the extrusion-forged sample with a consolidation temperature of 1100? had a lower consolidation level,and the sample contained pores.With higher consolidation temperatures of 1200? and 1300?,a higher powder consolidation level of the extrusion-forged samples was achieved.After vacuum annealing at 700? for 6h,the extrusion-forged samples had a fine ?-lamellar structure interposed with ? phase,and the thickness of the a lamellae was between 0.3 and 1 ?m.After the vacuum annealing treatment,the strength of the extrusion-forged Ti-6Al-4V alloy sample decreased,and the elongation to fracture was greatly improved.The microstructure of the region neasre the edge of the extrusion-forged sample was finer,its density was higher,and the strength and elongation to fracture were better.The tensile strength and elongation to fracture of the core regions and edge region of the extrusion-forged sample with a consolidation temperature of 1200? reached 1239±7 MPa,1269±4 MPa and 13.39±0.84%,16.79±0.72%,respectively.The ductile fracture was dominant,and no pores caused by the separation of the powder particles were found in the longitudinal section near the fracture surface of the tensile test specimens,indicating that the extrusion-forged sample reached a high level of powder consolidation in a shorter period of time.The powder thermomechanical consolidation process enables solid state recycled Ti-6A1-4V alloy and produces low cost,high performance extrusion-forged samples.The mechanical properties of hot extruded forged samples are inextricably linked to the microstructure of the samples,the content of interstitial elements,and the state of consolidation.