TNW钛合金1200度瞬时拉伸微观特征研究

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	TNW钛合金1200度瞬时拉伸微观特征研究
	金文锐
学位类型	硕士
导师	李阁平
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	Tnw钛合金显微结构 Gleeble瞬时拉伸晶粒长大扩散高温强化 Tnw Titanium Alloy Microstructure Gleeble Short-term Tensile Grain
摘要	"本文以TC4合金为参比，分析了TNW钛合金1200℃，36秒拉伸微观特征。在大量实验基础上，归纳了β相区晶粒长大动力学规律，分析了特殊显微形貌的形成机制，发现了影响高温变形抗力的主要因素。 TC4合金和TNW合金1000℃~1200℃/30~1800s晶粒长大的平均晶粒尺寸与时间和温度关系满足动力学方程：D2.31−170.52. 31=661.42t·exp(−283/RT) ( TC4合金)和D2.24−174.52.24=150.78t· exp(−324/RT)(TNW 合金)；合金晶粒长大激活能和元素扩散激活能的相近性表明合金在β相区晶粒长大是扩散相关过程。多视场原位观察发现，相同条件下TC4合金的晶界移动距离比TNW合金大，TNW合金的晶界移动速度较TC4合金慢。 1200℃，18s热模拟试验过程，TC4合金原始组织的细小片层和粗大片层均全部溶解；TNW合金原始组织中细小片层全部溶解，粗大片层部分溶解。TNW合金残留的粗大片层边缘呈模糊状，出现了特有的“模糊大片”显微形貌。TNW合金中Nb和W等合金元素迁移速度慢，易富集于晶界附近，在β→α相变与载荷的共同作用下，TNW合金形成晶界等轴链状分布α相。TEM观察发现：TC4合金晶界平直，TNW合金晶界弯曲，片层在晶界端为等轴小球状。 1200℃，36s，Gleeble热模拟拉伸结果为TC4合金变形抗力~2.5MPa，TNW合金~7.5MPa。基于错配球模型和强化叠加原理对两合金固溶强化的讨论结果表明TNW合金1200°C瞬时拉伸的变形抗力高于TC4合金的原因主要有以下两方面：1)TNW合金的合金元素固溶强化；2) TNW合金热模拟试验后的模糊大片对基体的“钉扎”作用。"
其他摘要	"Characteristic of microstructure in TNW titanium alloy was investigated during tension at 1200 °C for 36 s, while TC4 was also invited for comparison. Based on the bulk experimental results, the behavior of grain growth in the β phase region and the formation mechanism of the unique microstructure were discussed for revealing the main factors for controlling the high temperature deformation resistance. Kinetics of grain growth for TC4 (D2.31−170.52.31=661.42t·exp(−283/RT) and TNW (D2.24−174.52.24=150.78t·exp(−324/RT) at 1000 ~ 1200 °C for 30 ~ 1800 s shows the relationship between the mean grain size, incubation time and temperature; the consistency between the activation energy of grain growth and the diffusivity of alloying elements indicates that the mechanism of grain growth is of the diffusion-controlled case for both alloys. Based on in-situ observation, it shows the boundary migration distance of TC4 is farther than TNW at the present study condition. It indicated that the grain boundary migration rate of TNW is slower than TC4. During operation at 1200 °C for 18 s, the original microstructure of coarse primary lamellae and fine secondary lamellae quickly transform back to the β phase in TC4, leaving no interface in the β grain; while in TNW, the fine secondary lamellae fully transform back, leaving no interface in the original fine secondary lamellar region, but some interfaces are still visible in the β grain at the site between the original coarse primary lamella accompanying with the blurred tail at the end of the retained coarse lamellae, making an unique "blurred coarse lamellae" structure. The low diffusivity alloying elements, such as Nb and W in TNW, are easily segregation at the grain boundary, making the necklace-like equiaxed α distributed at the grain boundary during exposure to the cooperation of the phase transition from β to α and the load. TEM observation shows the straight and flat grain boundary in TC4, while the curvy grain boundary in TNW together with the necklace-like equiaxed α at which lamellae meet the grain boundary. Gleeble tensile results show that the stress of TC4 is ~2.5 MPa, and that of TNW is~7.5 MPa at 1200 °C for 36 s. Based on the model of mismatch ball and superposition principle, the capacity of solid solution strengthening has been discussed, and the reasons for the higher deformation resistance of TNW at 1200 °C compared to TC4 are as follows: 1) alloying elements in TNW show stronger solid solution strengthening; 2) the retained interfaces in TNW during thermomechanical processing, act as a “pin” in the matrix to drag the boundary and increase the deformation resistance."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64520
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	金文锐. TNW钛合金1200度瞬时拉伸微观特征研究[D]. 北京. 中国科学院金属研究所,2012.