| Porosity, pore type, pore size and pore distribution of porous titanium are the key factors affecting the mechanical properties and biocompatibility of porous titanium. Improving the porosity of titanium can reduce the elastic modulus to avoid stress shielding and related problems,but at the same time, it will lead to a significant reduction in strength. In order to prepare porous titanium material which satisfies the mechanical properties and biocompatibility of biological transplanting, porous titanium was prepared by powder metallurgic method and sintered by spark plasma sintering (SPS), Ti powder, TiO2 powder and TiH2 powder are used as raw materials, The mechanism and performance of the pore-forming were studied. In order to control the mechanical properties of porous titanium, TiO2 was used as the oxygen source to study the decomposition mechanism of TiO2 in Ti marix and the solid solution strengthening of oxygen. On this basis,TiH2 was used as the pore-forming agent to prepare porous titanium, raw materials are Ti powder,TiO2 powder and TiH2 powder. By changing the content of TiH2, the sintering process and parameters of porous titanium were explored to determine the optimum sintering process to conrol the pore characteristics including porosity, pore type, pore size and pore distribution, and the effect of TiH2 on porosity, phase, microstructure and mechanical properties of porous titanium were studied. The main contents and conclusions are as follows:Study on decomposition behavior of TiH2, TiO2, TiH2-TiO2 and Ti-TiO2-TiH2 mixed powders: The results of thermal analysis show that the decomposition temperatur of TiO2 is in the range of 500 ? to 810 ?: TiH2 undergoes fractional decomposition of TiH2?TiH4?Ti in the temperature range of 438 ? to 750 ?; In the system of TiH2-TiO2, the decomposition temperature of TiH2-TiO2 mixed powder is in the range of 440 ? to 730 ?, with the increase of the content ratio of TiH2 and TiO2 the endothermic peak of the mixed powder gradually decreases to the low temperature, the increase of content of TiH2 leads to the decrease of the decomposition temperature of TiO2, and with the increase of content of TiO2, the decomposition temperature of mixed powder gradually increases; In the systtem of Ti-TiO2-TiH2,when the content ration of TiH2 and TiO2 is in accordance with the content ratio of TiH2 and TiO2 in the system of TiH2-TiO2, the decomposition temperature of Ti-TiO2-TiH2 mixed powder is higher in the range of 480 ? to 780 ?, the addition of Ti in the system of TiH2-TiO2 causes the endothermic peak of the mixed powder to shift to high temperature.Effect of TiO2 on microstructure and mechanical properties of Ti matrix: With the sintering temperature rising from 800 ? to 1000 ?, the XRD diffraction peaks of Ti-1.0 wt..% TiO2 gradually skew to the left; Compared with pure Ti, TiO2 powder is viewed as a solid in the powder gap and it occupies part of the space before decomposing at low temperature, the oxygen atoms formed after decomposition diffuse or be dissolved into the Ti matrix, the original vacancies of the oxygen atoms are retained to form pores to play the role of pore forming. In addition, as the temperature increases, the sintering neck increases, the pores shrink or disappear, the density of sintering sample gradually increases, the porosity decreases, the pore size decreases, and the pore shape changes from irregular shape to spherosome; The oxygen atoms decomposed by TiO2 are dissolved in the Ti matrix to cause lattice distortion of Ti, which improves the hardness of Ti,when sintering temperature is 1000 ?, the microhardness of Ti is 260 Hv and the microhardness of Ti-1.0 wt.% is 318 Hv.Study on sintering process of porous titanium: Sintering by SPS, the sample is pre-filling with a 2 mm displacement at each end, the sample is subjected to the thermal preloading process at low temperature, when the punches of the both ends are displaced by 2 mm, the sample is in the pressureless sintering. When the sintering temperature rises from 900 ? to 1200 ?, there is a significant sintering neck between the powder particles, with the increase of temperature, the sintering neck gradually increases and the primary particle boundary of the powder disappears gradually; When the optimum temperature of sintering is 1200 ?, the pore shape is worm-like and spherical-shaped interconnection pore, the pore distribution is uniform.Effect of TiH2 on microstructure and mechanical properties of porous titanium: In the system of Ti-5%TiO2-xx%TiH2, with the content of pore-forming agent TiH2 increased from 20% to 50%,porosity increased from 29.43% to 35.22%; It is found that the pore size is between 3 and 30 ?m,and the pore shape of the porous titanium is changed from irregular ellipticity to irregular long striped ellipticity, and the pore type belongs to the interconnected open pore, with the increase of the porosity, the pores are gradually connected with each other, and the pores show a long strip in different directions making the connectivity of the pores larger; The addition of TiH2 promotes the decrease of decomposition temperature of TiO2, when the sintering temperature was 1200 ?,the decomposition of TiO2 was more thorough, and the more amount of oxygen is produced, the amount of Ti in the Ti matrix is increased, resulting in the diffraction peaks of Ti skewing to the left gradually; With the increase of content of TiH2 from 20% to 50%, the compressive strength of Ti-50%TiO2-x%TiH2 is reduced from 1023 MPa to 437 MPa, when the content of TiH2 is less than 50% the compressive strength of Ti-5%TiO2-50%TiH2 is larger than that of pure Ti,the compressive strength of system of Ti-5TiO2-x% TiH2 is larger than that of system of Ti-x% TiH2,which indicates that the oxygen atoms decomposed by TiO2 are dissolved in Ti matrix to solid solution reinforced porous titanium; In the system of Ti-5%TiO2-x% TiH2, because of the continuous decline of porosity, elastic modulus decrease from 10.42 GPa to 6.13 GPa, the elastic modulus of porous Ti-5%TiO2-x% TiH2 is larger than that of Ti-x% TiH2 due to the a-Ti stabilizing oxygen element decomposited by TiO2. |
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