| Particle-reinforced titanium matrix composites have high specific strength and thermal stability and good corrosion resistance,showing good application prospects in the aerospace field.At present,titanium-based composite materials for ? and ?+? matrix are mainly studied at home and abroad,and the composite materials of ? matrix are rarely involved.In this paper,the new preparation process of TiC particle reinforced titanium matrix composites and its relationship between microstructure and properties were investigated based on ?-titanium alloy Ti-32Nb-2Zr-2.8Mo.The main results are as follows:A new process for the preparation of composite materials was explored.A series of composite materials were prepared by the combination of high-energy ball-milling powder,SPS sintering and fusion casting method with nano-diamond as carbon source.The in-situ TiC particles were small in size,controllable in volume and uniform in distribution.In order to avoid the influence of impurity elements such as Fe,Cr and Ni introduced by the high-energy ball milling process and reveal the reinforcing effect of TiC particles,the manual mixing process is adopted in the subsequent processes.The effect of nano-diamond addition on the microstructure of as-cast composites was investigated.With the increase of nano-diamond addition,the content of TiC increased from 2.5 vol% to 7.5 vol%,and its morphology gradually grew into a striped structure from equiaxed small particles,eventually becoming coarse dendrites and distributed in the matrix.The uniformity of the distribution of TiC in the matrix becomes worse and worse.The effect of nano-diamond addition on the microstructure and properties of solid solution composites was investigated.After solution treatment at 1000 °C,it was found that the morphology and distribution of TiC showed the same regularity as the as-cast microstructure.Since the TiC particles provide a nucleation core for the solidification of the ? matrix and hinder the migration of the ? grain boundary during heat treatment,it is found that as the TiC content increases,the ? grains are remarkably refined,and the strength of the composite material gradually increases;In terms,the increase in TiC content causes the elastic modulus of the composite to gradually increase.The effects of aging treatment at 450 °C to 550 °C on the microstructure and properties of composites were investigated.It is found that at the same aging temperature,with the increase of nano-diamond content,the generated TiC can provide more core for the precipitation of ?-phase in the ?-matrix,increase the precipitation of ?-phase and refine its size,and TiC can also be fine.The beta crystallites result in an increase in the strength and modulus of elasticity of the composite and a decrease in elongation.When the aging temperature increases,the precipitation of TiC increases and gradually coarsens,while the ? phase content decreases and coarsens,which leads to a decrease in the strength and elastic modulus of the composite,and an increase in elongation.A 7.5 vol% TiC reinforced composite was prepared by using graphite powder as carbon source.The influence of cooling process on its microstructure and properties was studied.Compared with the slow cooling process,the composite material prepared by the rapid cooling process has a significantly reduced TiC particle size and uniform distribution,and the ? phase content precipitated by the aging is higher and finer,which makes the composite mechanical properties better..The above work provides a new way to optimize the comprehensive mechanical properties of titanium matrix composites. |
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