| The medical metastable ?-type Ti-12Cr alloy has low elastic modulus,good biocompatibility and corrosion resistance,and is one of the candidate materials for spinal internal fixation materials.Although Ti-12Cr alloy prepared by traditional vacuum casting technology has excellent biocompatibility and low elastic modulus,it still has problems such as original coarse grains,segregation of components,and difficulty in subsequent cold working.Powder metallurgy technology has the advantages of near-net shape,low production cost,small original grains,and easy organization control,in this study,powder metallurgy technology was used to prepare medical Ti-12Cr alloy,the original grain size and microstructure were adjusted,the structure evolution and the changing rule of mechanical properties were analyzed.The specific research work is as follows:Using TiH2,pure Ti,and pure Cr powders as raw materials,the effects of powder particle size,powdering method and preparation technology on the microstructure,original grain size and mechanical properties of Ti-12Cr alloy are analyzed.The results show that the original grain size of powder metallurgy Ti-12Cr alloy is much smaller than that of traditional ingot metallurgy Ti-12Cr alloy.The original grain size can be reduced from 314 ?m to less than 107?m;changing the particle size of TiH2 powder can control the original grain size of the alloy;when the particle size of TiH2 powder is reduced from 31 ?m to 4 ?m,the original grain size of the alloy is reduced from 107 ?m to 62 ?m;the original grain size of the alloy is further reduced to 42 ?m after the mechanical ball milling of the raw material powder for 10 h;as the grain size decreases,the yield strength of the alloy increases,and both meet the requirements of Hall-Petch relationship,Hall-Petch coefficient k=29.2 MPa·mm1/2,which is much higher than secondary industrial pure titanium,indicating that the fine-grain strengthening effect of Ti-12Cr alloy is significant;Using stearic acid as carbon source,pure Ti and pure Cr as raw materials,TiC/Ti-12Cr alloy was prepared by in-situ autogenous method.The effects of sintering temperature,SA content and sintering method on the microstructure,grain size,TiC particle size and morphology and mechanical properties of the alloy were analyzed.The results show that the formation of TiC particles inhibits the growth of ? grains,and the grain size of the alloy is less than or equal to 35 ?m;when the sintering temperature is increased from 950? to 1150?,the grain size increases from 14 ?m to 35 ?m,TiC particles grow from 3 ?m to 5 ?m,when the sintering temperature is 1150?,the alloy reaches sintering densification,the particle morphology changes from equiaxed to irregular shapes;when the SA content in the alloy is 1 wt.%,while the yield strength is improved,the elastic modulus remains at a low level,and the plastic strain decreases little,when the SA content is increased from 1 wt.%to 2 wt.%,there is no significant change in the grain size and particle size of the alloy,and the grain morphology changes from equiaxed to irregular shape,? phase is precipitated at the ? grain boundary and within the grain,the yield strength increased significantly,from 1399 MPa to 1569 MPa,fracture strain decreased from 24.0%to 1 1.4%. |
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