The Effect Of MDF Deformation On Microstructure And Property Of Pure Titanium

Pure titanium is a widely used metal material,it is more biocompatible than titanium alloy and has a bright future in medical applications.But its low strength and poor wear resistance made these applications limited to a great extent.Therefore,it is of great theoretical significance and engineering application value to develop a forging process for high strength pure titanium forgings.This paper took the commercial pure titanium TA1 as the research object.The grain refinement and mechanical properties of the material were improved by multidirectional forging.And the effect of various factors on grain refinement and mechanical properties was analyzed.The process parameters were optimized step by step.Finally,a more practical fine grain strengthening forging process was proposed.A series of studies were carried out on the microstructure and mechanical properties of the forged specimens.1.In order to refine the grain of pure titanium and improve its mechanicalproperties,the forging process of pure titanium TA1 was studied.The effects of deformation temperature,forging cycle,quenching,holding time and deformation of single pass on Microstructure and mechanical properties were studied,and the forging process was optimized step by step.The results show that:The commercial pure titanium TA1 needs to be insulated at 500? for 15min before forging.Then,3 cycles of multi-direction forging were carried out,the single pass deformation amount was 50%,the water quenching 5s was finished immediately after each pass,and the holding time of each pass was 5min.Finally,the uniform fine equiaxed grains with average grain size of 0.3?m can be obtained.2.The microstructure uniformity and microstructure evolution mechanism of pure titanium TA1 under multiaxial forging deformation were studied.The results show that:By observing OM in different regions of each cycle sample after multi-direction forging,it was found that the grain refinement of the edge of the sample was inferior to that of the core.However,with the increase of forging cycle,the fine grain zone gradually extends to the periphery.After 3 cycles,the grain size of the edge of the specimen was close to the center and tends to be uniform.TEM results show that uniform equiaxed fine grains after 3 cycles of forging were the result of continuous dynamic recrystallization.3.The surface hardness distribution of pure titanium sample was studied by microhardness contour diagram,and the hardness uniformity was analyzed.The results show that:(1)Although the deformation was not uniform,the average microhardness increases with the increase of strain.The area of the minimum microhardness region observed around the edge of the sample decreases with the increase of the number of multi-directional forging cycles.These observations qualitatively indicate that the deformation uniformity was well improved with the increase of strain.(2)The microhardness contour diagram shows that the deformation uniformity was improved better at higher strain,and the quantitative reduction of the inhomogeneity factor(IF)in the later strain state was confirmed quantitatively..4.The tensile properties of ultrafine grained pure titanium specimens were studied.The results show that:With the increase of forging cycle,the yield strength and tensile strength of pure titanium TA1 specimens could be obviously improved.When the cumulative plastic strain was 4.5,the yield strength was 2.59 times as much as that of the coarse grained titanium before forging.The significant improvement of strength properties was attributed to the increase of dislocation density and grain size reduction.5.In order to better understand the change of material strength and plasticity,the tensile fracture surface was analyzed by SEM.The results show that:After more than forging for 1 to 3 cycles of pure titanium TA1 tensile specimen fracture was shear fracture.The macroscopic fracture was about 45°from the maximum tensile normal stress.The fracture mechanism was the coalescence and coalescence mechanism of microporous polymerization.In short,in this paper,the microstructure and hardness uniformity of commercial pure titanium TA1 were studied based on the proposed fine grain strengthening forging process.At the same time,the tensile properties of the forged samples were also studied.The results show that the forging cycle increases with the increase of the forging cycle.The results show that with the increase of forging cycle,the microstructure and hardness uniformity were improved gradually.Grains were continuously refined,and the yield strength and tensile strength were improved significantly.