Ti₃Al/TiC+Al₂O₃多元复合材料的制备和性能研究

【作者】 李江田；

【导师】 孙康宁；

【作者基本信息】 山东大学 ， 材料学， 2005， 硕士

【摘要】 对工程结构陶瓷性能要求日趋苛刻的今天,发展具有优异综合性能的复相陶瓷成为工程材料设计的关键。通过添加金属元素、陶瓷颗粒、纤维晶须等增强相可以提高陶瓷材料的韧性和强度,但是都不同程度存在着一定的缺陷。而金属间化合物表现出期望的优异性能,如何使陶瓷材料和金属间化合物性能达到优势互补是发展的必然方向。目前报道金属间化合物增韧主要集中在Fe-Al、Ni-Al系,关于Ti-Al金属间化合物和颗粒协同增韧的报道很少。因此本课题首先对Ti/Al混合粉末进行机械合金化,然后和基体粉末通过热压反应烧结制备Ti-Al金属间化合物增韧陶瓷基体（TiC+Al₂O₃）复合材料。主要工作和实验结果简单概括如下: 首先对Ti/Al混合粉末进行机械合金化。经过强烈的机械球磨,Ti、Al晶体的结构、形貌发生很大的变化。在很短的时间内就可以细化晶粒。在碰撞和剪切应力下引入大量的缺陷和内应力,相继出现过饱和固溶体、非晶、金属间化合物等物相。利用规则溶液模型研究了合金化过程中固溶体的相对稳定性,提出了（Al摩尔比,温度）坐标判别模式,理论计算结果表明在本实验中主要形成Al在Ti中的固溶体,这与实验结果相吻合。 通过选择合适的烧结制度,利用热压反应烧结成功地制备了Ti₃Al/TiC+Al₂O₃多元复合材料。金属间化合物Ti₃Al对（TiC+Al₂O₃）有明显的增韧补强效果,抗弯强度和断裂韧性分别增长150%和220%;在1550℃烧结的材料具有较好的综合性能,硬度可以达到91.5HRA,抗弯强度为623.33MPa,断裂韧性为8.02MPa·m^1/2,致密度可达96.8%。由于1650℃烧结试样中存在晶粒异常长大,使性能有所降低。 在700℃,900℃对Ti₃Al/TiC+Al₂O₃复合材料进行热处理,热处理对韧性和硬度没有明显的影响,但是使1650℃烧结试样的强度明显降低。研究了复合材料在200、400、600、800、900、1000℃下连续氧化行为,结果表明在900℃时复合材料质量增加明显。 在Ti₃Al/TiC+Al₂O₃复合材料的基础上,分别加入5wt%、8wt%、10wt%纳米TiC颗粒,研究了纳米颗粒的增韧机理和纳米颗粒含量对复合材料结构性能的影响。纳米TiC颗粒的加入促进了均匀、细化结构的形成,复合材料中具有晶内更多还原

【Abstract】 Facing to the rigorous working environments, composites with comprehensive properties have become an important direction for the development of engineering structural ceramics. The toughness and strength of ceramics can be improved with addition of metal elements, ceramics particles, whiskers and fibers, however, shortcomings in oxidation resistance, wetting and application at high temperature limit the fraction of the additives. Meanwhile, the intermetallics exhibit some excellent properties expected. And it is inevitable for materials experts to find a compatible combination of both merits. But up to now, the intermetallics reinforced composites mainly focus on Fe-Al system and Ni-Al system, and information about intermetallics o f Ti-Al system as reinforcing phases was little documented. S o this subject wants to prepare the Ti-Al intermetallics reinforced multi-composites with a matrix of TiC+Al2O3 by hot-pressing reaction sintering matrix powders and MAed Ti/Al powder mixture. And the main jobs and results are simply generalized as follows:First, the Ti/Al powder mixture was mechanical alloyed (MAed) by high-energy ball milling. After serious mechanical treatment, the structures and properties of Ti and Al elements undergo larger changes, and the grains can be refined to nanometer in very short time. Due to the introduction of defects and inner stresses under the collision and wear stresses, supersaturated solid solution, amorphous phases and intermetallics formed in consequence during ball milling. The relative stability of solid solution in mechanical alloying was studied according to regular solution model, and a new method using coordinate form of (mole fraction of Al, temperature) was proposed to evaluate the relative stability. The model suggests that in this experiment the solid solution of aluminum in titanium elements is dominant, according with the experimental results.With proper sintering processes, Ti3Al/TiC+Al2O3 multi-composites were prepared successfully by hot-pressing reaction sintering. The matrix was reinforced by intermetallics remarkably, and the bending strength and fracture toughness ofmulti-composites was improved by 150% and 220% respectively. The samples sintered at 1550℃ have better properties with the hardness over 91.5HRA, bending strength 623.33MPa, fracture toughness 8.02MPa.m1/2 and relative density 96.8%. But abnormal grain growth makes properties of samples sintered at 1650℃ decrease. The composites were heat treated at 700 ℃ and 900 ℃ in air atmosphere for 1 hour. Short-term heat treatment has a neglectable effect on hardness and toughness, but makes an remarkable decreasing in the strength of composites sintered at 1650 ℃. And the continuous oxidation behavior at 200, 400, 600, 800, 900, 1000℃ was also studied, the results show that serious mass increasing occurs at 900 ℃, which agrees with the data in the former documents.On the basis of composites mentioned above, the reinforcing mechanisms and effects of the weight fraction of nano TiC particles on the properties of the composites were discussed by adding 5wt%, 8wt%, 10wt%nano particles into the composites. Nano TiC particles facilitate the formation of uniform and refined structures. And not only the intergranular and intragranular nano-structures, but also intragranular structure of Al2O3 in Ti3Al and elongated TiC grains were found in nano particle reinforced composites. The results also show that the mechanical properties including relative density, strength and toughness have been greatly improved by different reinforcing mechanisms of nano particles such as grain-refining, residual stresses and drawing effect of elongated grains and so on. However, the properties of composites as the function of weight fraction of nano TiC particles were characterized as increasing firstly and then decreasing. In this experiment, the sample with 8wt% nano TiC particles owns the most excellent mechanical properties: the relative density over 99.5 %, bending strength 819MPa and fracture toughness 14.06MPa·m1/2.According to the experimental results, there are some new viewpoints in the present study:1) The relative stability of solid solutions in MAed Ti/Al powder mixture is studied according to regular solution model. And on this basis, a new method using coordinate form of (mole fraction of aluminum, temperature) is proposed to evaluate the relative stability of solid solutions.2) Ti3Al/TiC+Al2O3 multi-composites were prepared successfully by hot-pressing reaction sintering. And the composites possess excellent mechanical properties.3) The effects of nano TiC particles on the structures and properties of composites are investigated. Besides the intragranular structure of nano TiC particles in matrix, intragranular structure of alumina in Ti3Al and elongated TiC grains are also observed, which contribute to the great increasing of mechanical properties.更多还原