Study On Preparation And Hot Deformation Behavior Of?Micro TiB+nano Y₂O₃? Reinforced Titanium Matrix Composites

Based on the advantages of lightweight high strength and excellent high temperature performance,titanium matrix composites have potential application prospects in aerospace and automotive industries.However,poor plasticity and large high-temperature deformation resistance of titanium matrix composites limit their large-scale engineering applications.Nano-sized particles can refine grains while increasing strength and plasticity.In this paper,?TiB+Y₂O₃?/Ti composites with different volume ratios were prepared by vacuum induction melting method,and the effects of different volume ratios on the microstructure and properties of the relative composites were studied.The microstructure and properties of composites under different deformation parameters are explained.The processing parameters were optimized,and multi-directional forging?MDF?were adopted to prepare bimodal size particles?micro+nano-meter?reinforced high temperature titanium matrix composite with fine grains and excellent mechanical properties.The dynamic recrystallization behavior,high temperature deformation mechanism and strengthening mechanism of the composites can be revealed.During the smelting process,Ti and TiB₂ react in situ to form Ti B,and the nano-sized Y₂O₃ particles are generated by adding Y₂O₃ solution-precipitation mechanism.TiB whiskers and Y₂O₃ particles are relatively distributed in the matrix.The introduction of the reinforcements causes a significant refinement of?lamellar colony.With the TiB/Y₂O₃ volume ratio reduced,the size of?colony gradually decreases.When TiB/Y₂O₃ volume ratio is up to 4:1,the sizes of?colony decrease from 63.1?m to 29.3?m.Further decreasing Ti B/Y₂O₃ volume ratio,there is little change in size.Compressive strength increases with decreasing TiB/Y₂O₃ volume ratio,and elongation increases first and then decreases.On the basis of the above experimental results,titanium matrix composite with TiB/Y₂O₃ volume ratio of 4:1 was subjected to hot compression deformation under different deformation conditions.The results show that,the peak stress of the composite decreases with increasing temperature and decreases with decreasing strain rate.In??+??phase region,the thermal activation energy of the composite is 534.71KJ/mol.In?phase region,the thermal activation energy is 207.63KJ/mol,and the constitutive equation can be established correspondingly.According to the analysis results,in??+??phase region,the softening mechanism is mainly attributed to the dynamic recovery and dynamic recrystallization of?phase.In?phase region,the softening mechanism results from the dynamic recrystallization of?grains.From the hot working diagram,it can be well found that the appropriate thermal processing window is 950^oC?1020^oC,0.003s^-1?0.1s^-1,in??+??phase region,and 1080^oC?1140^oC,0.01s^-10.55s^-1,in?phase region.The matrix alloys and composites selected were multi-directionally forged at 1010^oC,and bimodal size particles?micro+nano-mater?reinforced titanium matrix composites with fine grain and uniform particles were successfully prepared,and the performance was excellent.At room temperature,tensile strength reaches up to 1470.5MPa,elongation of 7.2%.The increase in strength is mainly due to fine grain strengthening,Orowan strengthening and load transfer strengthening.For the enhancement of elongation,apart from fine grain strengthening,micron-sized particles contribute to stable deformation and induce strain hardening.The dispersed distribution of nanoparticles can generate and store dislocations without causing local cracks in the grain boundaries.Multi-directional forging distorts grain orientation,coordinates deformation,and facilitates substrate slip.At 650^oC,the tensile strength can reach 803.3MPa,and the strength decreases with the temperature rising.This indicates that fine-grain strengthening does not work above 650^oC,and the Orowan strengthening also decreases,while the load strengthening dominates.At 700^oC or more,the reinforcement and matrix are debonded,the carrying capacity of which is reduced,and the strength is reduced.The elongation increases sharply with the increase of temperature,which is attributed to the softening of the matrix.