【作者】 孙拴利；

【导师】 吕维洁；

【作者基本信息】 上海交通大学 ， 材料学， 2011， 硕士

【摘要】 随着航空航天工业的发展,具有高强度、高弹性模量、低密度的高温钛合金受到了广泛关注。而钛基复合材料具有比钛合金更高的比强度、更优异的高温性能和蠕变性能,因此具有广阔的应用前景。然而高温变形塑性差、流变应力大、设备要求高等特点使高温钛合金基复合材料的热加工变得困难,从而大大限制了这种材料的实际应用。近些年发展起来的热氢处理技术,能够改善钛合金的高温塑性,降低热变形的流变应力和成形温度,这为改善高温钛合金基复合材料的热加工性能提供了一条新的思路。本工作便是针对高温钛合金基复合材料的难加工问题,首先原位合成了综合性能良好的Ti-1100基复合材料,研究了置氢材料的微结构、相变点以及显微硬度,进行了超塑性研究,简单探讨了失效机制。得出如下主要结论:利用钛、碳化硼粉末和石墨之间的反应,在真空自耗炉中两次重熔制备了三种不同增强体含量的Ti-1100基复合材料。拉伸试验发现,随着增强体体积分数增加钛基复合材料的室温和高温强度都明显提高,室温和高温延伸率分别在13%和23%以上。研究了钛基复合材料置氢后微结构、相变和显微硬度的变化。过量氢元素的加入导致钛基复合材料中少许氢化物的析出,由于氢的渗入,Ti相晶格膨胀,晶格常数变大;置氢显著降低了两种Ti-1100基复合材料的相变温度;另外,其显微硬度也都由于氢的加入而降低。高温超塑拉伸试验中,增强体含量为5 vol.%时,置氢Ti-1100基复合材料最大延伸率为294%;而10 vol.%(TiB+TiC)增强钛基复合材料最大延伸率为256%。在研究温度范围内,置氢明显提高了材料的延伸率。置氢显著降低了两种Ti-1100基复合材料的最佳超塑变形温度和流变应力,提高了最佳初始应变速率;流变应力随温度升高而下降,随初始应变速率增大而增加;另外氢的加入还降低了Ti-1100基复合材料的变形激活能。分析了不同初始条件变形后的微观形貌,较低的应变速率不一定得到较高的延伸率是因为在高温下较长时间晶粒的再结晶长大会降低了材料塑性。变形前后SEM照片对比分析发现,高温拉伸最终断裂是增强体与基体界面脱粘形成裂纹或空洞而后扩展导致的。更多还原

【Abstract】 With the development of aeronautics and space industry, high temperature titanium alloys which possess great ultimate strength, high module and low density have abstracted great attention. The titanium matrix composites due to higher specific strength, more excellent high-temperature resistance and creep performance illustrate a good prospect of application. However, poor plasticity and high flow stress at high temperature and high demanding for equipments result in the difficulty of working of TMCs, restricting largely their application in practice. Thermohydrogen treatment (THT) as a newly developed technology can improve the high-temperature plasticity of titanium alloys, decrease the flow stress and processing temperature during hot working, which supplies a new method for ameliorating poor hot-working character of TMCs. To overcome the hot-working difficulty of TMCs, in the work, Ti-1100 matrix composites with good comprehensive mechanical properties was prepared using in-situ technology. The microstructure, phase transformation temperature and micro hardness of hydrogenated TMCs were studied. In addition, the studying of the superplastic behavior and failure mechanism was also carried out. The main conclusions were listed as follows.Based on the reaction among titanium, B4C powder and graphite, three kinds of Ti-1100 matrix composites with different reinforcement content were prepared by consumable vacuum arc remelting (VAR). It was found from tensile test that as hydrogen content increased the ultimate tensile strength at room temperature and elevated temperature increased evidently, and the elongations were more than 13% and 23%, respectively.The microstructure, phase transformation and microhardness of hydrogenated Ti-1100 matrix composites were studied. The addition of plenty of hydrogen leaded to the precipitation of hydride. And the infiltration of hydrogen resulted in titanium lattice expansion, largening the lattice constant. The results indicated a decrease inβtransus temperature of TMCs with an increase in hydrogen content. Moreover, the microhardness also decreased after hydrogenation.In high-temperature tensile test, the maximum elongation of hydrogenated TMCs with reinforcement content of 5 vol.% was 294% while that of 10 vol.% (TiB+TiC)/Ti-1100 composite was 256%. Within the studied temperature range, hydrogen increased the elongation in tentile test.Hydrogen decreased the optimal superplastic temperature and flow stress and increased the optimum superplastic strain rate for two kinds of TMCs. The flow stress decreased with the test temperature increment, and increased with the initial strain rate. Furthermore, due to the addition of hydrogen the activation energy Q of TMCs had a decrease.According to the microstructure analysis after deformation under different condition, the lower strain rate didn’t always mean the better elongation, which was because grain recrystallized and grew at high temperature for a long time. It can be seen based on SEM analysis of hydrogenated TMCs before and after deformation that the failure in tensile test was probably ascribed to the cracks or cavities resulting from debonding interface between matrix and reinforcement.更多还原