泡沫钛的结构和力学性能预测研究

发布时间：2019-03-29 09:55

【摘要】：孔隙率和力学性能的预测问题是泡沫钛所有制备方法都面临的重大难题,特别是当前泡沫钛的研究还停留在实验室阶段,使得这一问题变得尤其重要。目前,国内外尤其是美欧日等发达国家虽对此问题已有所重视,但还处于初步研究阶段。本文对此进行了有益的尝试,在文献综述的基础上,研究了造孔剂的不同参数下所获得的孔隙率和力学性能及它们的重复性,深入分析了孔隙率与造孔剂含量之间的关系,得到了一些有价值的成果。本文的主要研究贡献如下:(1)综述了泡沫钛的制备进展。本文全面总结了2004年以来新出现的泡沫钛制备方法,并进行了分类介绍。通过比较这些方法的技术特点,提出了泡沫钛制备方法的发展趋势。(2)综述了造孔剂技术制备泡沫钛的研究现状与进展。本文全面总结了制备泡沫钛用的所有造孔剂。通过分类介绍这些造孔剂的特点,指出了造孔剂技术制备泡沫钛领域的发展方向。(3)针对高孔隙率泡沫钛制备困难的特点,提出了基于造孔剂的热分析实验结果来选择合适的脱除工艺的思想。本文采用热分析仪来测定尿素的热重和差示扫描量热曲线,根据这些曲线来选择尿素的脱除气氛、加热速率和终止温度,由此解决了制备高孔隙率泡沫钛的坍塌问题。再将造孔剂的脱除和钛粉的高温烧结分两步单独进行,有效的避免了钛粉表面的氧化问题。在造孔剂含量超过60%的情况下,制备出了孔隙率介于50.2-71.4%的泡沫钛。结果表明,孔隙率小于造孔剂含量。(4)给出了造孔剂的粒径大小影响孔隙率的理论解释。本文通过筛分获得了3个不同粒径分布的造孔剂颗粒。在造孔剂含量相同的情况下,结果表明孔隙率一方面全部小于造孔剂含量,另一方面随着造孔剂粒径的减小而微弱的减小。通过假设宏观大孔在烧结过程发生体积收缩,分析表明宏观大孔在烧结过程的体积收缩量随着造孔剂粒径的减小而微弱的增大。(5)提出了孔隙率和力学性能的重复性概念。结果表明,孔隙率具有重复性,而力学性能重复性比较差,但可通过增大造孔剂的含量或减小造孔剂的粒径大小来提高力学性能的重复性。通过讨论,力学性能重复性差主要归因于宏观大孔分布的不可控性等因素造成的。(6)论证了宏观大孔在烧结过程的体积变化。通过理论联系实际,证明得到宏观大孔在烧结过程发生体积收缩现象。当宏观大孔的体积减小量大于骨架上微观小孔的体积时,会导致孔隙率小于造孔剂含量。(7)建立了孔隙率与造孔剂含量的数学模型。通过理论联系实际,证明得到孔隙率与造孔剂含量呈线性关系,实现了孔隙率的预测。再结合Gibson-Ashby模型方程,实现了通过造孔剂含量来预测力学性能。
[Abstract]:The prediction of porosity and mechanical properties is an important problem in the preparation of titanium foams. Especially, the research of titanium foams is still in the laboratory stage, which makes this problem more and more important. At present, the developed countries, especially the United States, Europe and Japan, have paid attention to this problem, but they are still in the preliminary research stage. On the basis of literature review, the porosity, mechanical properties and repeatability of pore-forming agent under different parameters were studied, and the relationship between porosity and content of pore-forming agent was analyzed. Some valuable results have been obtained. The main contributions of this paper are as follows: (1) the progress in the preparation of titanium foams is reviewed. In this paper, the preparation methods of titanium foams have been summarized and classified. By comparing the technical characteristics of these methods, the development trend of preparation methods of titanium foam was put forward. (2) the research status and progress of preparation of titanium foam by pore-forming agent technology were reviewed. All the pore-forming agents used in the preparation of titanium foam are summarized in this paper. This paper introduces the characteristics of these pore-forming agents and points out the direction of development in the preparation of titanium foam by pore-forming technology. (3) in view of the difficult preparation of titanium foam with high porosity, it is pointed out that it is difficult to prepare titanium foam with high porosity. The idea of selecting the appropriate removal process based on the experimental results of thermal analysis of pore-forming agent was put forward. In this paper, thermogravimetric and differential scanning calorimetry curves of urea are measured by thermal analyzer. According to these curves, the atmosphere of urea removal, heating rate and termination temperature are selected to solve the collapse problem of preparing titanium foam with high porosity. The removal of pore-forming agent and high-temperature sintering of titanium powder are carried out separately in two steps, thus effectively avoiding the oxidation of titanium powder surface. When the content of pore-forming agent is more than 60%, titanium foams with porosity between 50.2 and 71.4% have been prepared. The results show that the porosity is less than the content of pore-forming agent. (4) the theoretical explanation of the effect of pore-forming agent size on porosity is given. In this paper, three pore-forming agent particles with different particle size distribution were obtained by sieving. When the content of pore-forming agent is the same, the porosity is lower than that of pore-forming agent on the one hand, on the other hand, the porosity decreases slightly with the decrease of pore-forming agent particle size. The volume shrinkage of macropores during sintering process is assumed to increase slightly with the decrease of pore size. (5) the concept of repeatability of porosity and mechanical properties is put forward. The results show that the porosity has repeatability, but the mechanical property repeatability is poor. However, the repeatability of mechanical properties can be improved by increasing the content of pore-forming agent or decreasing the particle size of pore-forming agent. It is discussed that the poor repeatability of mechanical properties is mainly due to the uncontrollability of macro-pore distribution and other factors. (6) the volume change of macro-pore in sintering process is demonstrated. According to the theory and practice, it is proved that the macro-pore shrinkage occurs in the sintering process. When the volume reduction of macropores is larger than that of micropores on the skeleton, the porosity will be smaller than the content of pore-forming agent. (7) A mathematical model of porosity and pore-forming agent content has been established. According to the theory and practice, it is proved that the porosity is linearly related to the content of pore-forming agent, and the prediction of porosity is realized. Combined with the Gibson-Ashby model equation, the mechanical properties can be predicted by the content of pore-forming agent.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.23

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