上海交通大学硕士学位论文 目 录 i原位自生颗粒增强原位自生颗粒增强 7715D 基复合材料的超塑性研究基复合材料的超塑性研究 摘摘 要要 钛合金由于比强度高、抗蚀性优异，已成为航空航天工业、化学工业、医药工程和休闲行业优先选用的材料传统高温钛合金只能在略高于 500oC 的温度下使用，不能满足航空航天等领域的应用需求原位合成陶瓷颗粒增强钛基复合材料能大幅提高材料的比模量、比强度和蠕变性能，进一步提高使用温度以满足航空结构材料不断发展的需要但钛基复合材料难以加工，这限制了它的应用和发展用超塑成型的近终成型技术（near-net shape）生产金属基复合材料构件，不但可以节省材料消耗，还可以大幅降低加工成本，因此受到广泛关注 本文以在航天领域获得应用的 7715D 钛合金为基体，利用钛与 B、C 或 B4C 之间的化学反应经普通熔炼和热加工工艺制备了不同体积含量的 TiB、TiC 和两者混合增强的 7715D 钛基复合材料，以期提高 7715D钛合金的使用温度XRD 分析表明：可以合成不同含量、不同类型颗粒增强体强化的 7715D 基复合材料。
经热处理得到网篮组织材料后，其室温、高温力学性能测试表明：增强体为 2vol.%时，TiC/7715D 综合力学性能最好，TiB/7715D 的最次；但随体积分数的增加，TiC/7715D 的力学性能提高不大，TiB 提高明显；含量为 5vol.%(TiC+TiB)/7715D 在 650oC时的高温力学性能与基体 600oC 相当 测试了基体 7715D 钛合金及其复合材料的超塑性能，并观察其超塑变形前后的组织特征结果表明：等轴基体的最大延伸率为 1144%，等上海交通大学硕士学位论文 目 录 ii轴 TiC/7715D 的最大延伸率为 802%， 但存在一个转折点； 网篮基体的延伸率达到 730%，2vol. %网篮（TiC+TiB）/7715D 则达到 625%以上复合材料与基体的应力应变曲线形状各异，且均出现二次硬化现象等轴基体与等轴 2vol.% TiC/7715D 在初始应变速率不高于 10-3s-1，温度高于950°C 时，出现二次硬化现象；网篮基体与网篮为 2vol.%的（TiC+TiB）/7715D 在初始应变速率小于 10-3s-1，温度高于 1025°C，才出现二次硬化现象。
与等轴初始组织材料相比，网篮初始组织材料也能获得较好的超塑性， 超塑性能的好坏取决于超塑变形过程中的微观组织而非初始组织，二次硬化现象伴随有粗大晶粒现象 分析表明该基体与复合材料超塑机理主要是动态回复与动态再结晶调节的晶界扩散及晶粒长大行为析出相通过影响相变点产生网篮组织来调节变形过程中动态回复与动态再结晶的比例，以及弥散分布起到钉扎位错、阻碍晶粒长大来影响超塑行为温度段与应变速率使得控制动态回复与动态再结晶的扩散机制改变，从而在不同温度段下不同应变速率晶粒长大倾向不同，从而引起二次硬化现象的产生条件不同 关键词：关键词：耐热钛基复合材料，网篮组织，二次硬化，超塑性 上海交通大学硕士学位论文 目 录 iiiSTUDY OF SUPERPLASTICAL BEHAVIOR OF IN-SITU PARTICLE REINFORCED 7715D MATRIX TATUNIUM COMPOSITES ABSTRACT Titanium alloys, with high specific strength, good specific modulus and resistance to elevated temperatures, become to one of the most popular materials in aerospace and chemical industrial, medical and domestic applications. Particle reinforced titanium matrix alloy, prepared by in situ technique, have considerable potential for improvement in properties and service temperature,while conventional high temperature titanium material can’t meet some application requirements in aerospace industry because of its limited use temperature as 500oC.But its application is also limited for its poor machining performance. In order to solve these problems, superplastic deformation (one way of near-net shape）of materials can be used, which will save raw material and reduce the cost. In this paper, in order to improve the operating temperature of 7715D, an alloy applicated in aerospace industry, TiB, TiC, TiB and TiC particales have been prepared by general casting technology utilizing the self-propagation high-temperature synthesis reactions between titanium and B4C, graphite by in situ technique. XRD results show that those particale reinforced titanium matrix composites were produced successfully with different types and volumes. Materials with basket-weave microstructures were got by heat-treatment and then mechanical properties were tested, and results show that:with 2vol.% particales, the best overall mechanical properties belong to TiC/7715D and the second to TiB/7715; with particles included increasing, the mechanical properties of TiC/7715D 上海交通大学硕士学位论文 目 录 ivimprove little while TiB reinforced improve significantly; with 5vol. % particles, the high temperature mechanical properties of (TiC+TiB)/7715D at 650oC are similar to those of 7715D alloys at 600oC. The superplasticity of those composites and the matrix alloy has been studied respectively. With initial equiaxed microstructure, a maximum elongation of 1144% was obtained with different types of true strain-true stress curves in 7715D alloy and a maximum elongation of 802% was observed in 2vol.%TiC/7715D concurrent with a turning point in its elongation-temperture curve and same different true strain-true stress curves,while the second work hardening behavior was observed when the temperature is above 950oC with initial strain rate not above 10-3s-1；with basket-weave initial microstructure, a maximum elongation of 730% and 625% were obtained with similar true strain-true stress curves in 7715D alloy and 2vol. %（TiC+TiB）/7715D,respectively. But the second work hardening behavior was observed while the temperature is above 1025oC with initial strain rate slower than 10-3s-1. Superplastic average activation energies involved were calculated and microstructure involved were observed.Analyse shows that, good superplasticity depends on microstructures during deformation process other than initial shapes.The superplastical deformation mechanism of those composites is mainly Dynamic Recovery / Dynamically Recrystallization concurrent with Grain Boundary Sliding /Grain Coarsening controlled by different diffusion mechanisim,which is effected by temperature and initial strain rate.Precipitates involved effect the ratio of Dynamically Recrystallization by pinning dislocation,inhibiting 。