强变形加工Co基和Ti基先进合金材料的结构与性能调控

发布时间：2018-05-03 17:52

本文选题：强变形 + 热处理　；参考：《燕山大学》2016年博士论文

【摘要】：强变形技术通过对金属材料在外力作用下进行强烈的塑性变形,使其处于高能量状态,这为调控材料的微结构提供很大空间;经过后续的热处理来释放能量,可能获得具有特殊微结构低能量状态材料,并呈现出与未经过强变形加工完全不同的结构与更加优异的性能。然而,针对不同的材料体系需要采用不同的强变形技术及后续的不同的热处理工艺。本文以SmCo/a-(Fe,Co)纳米复合永磁材料、TiZrAlV合金以及TiNi形状记忆合金为研究对象,分别采用高能球磨、多道次轧制和电塑性轧制三种不同的强变形工艺以及后续的热处理和拉伸等方式,分别获得了双相纳米晶、多相多尺度结构以及单相纳米晶材料,采用X射线衍射分析(XRD)、透射电子显微分析(TEM)、差示扫描量热分析(DSC)以及微力拉伸试验机(Instron 5948)等技术,深入研究三种材料在强变形及后续热处理和拉伸等过程中微结构的演变,并针对不同材料分别探讨其纳米晶形成机制、力学性能和变形机制。采用高能球磨技术制备了两种不同软磁相成分的部分晶化非晶合金SmCo/Fe和SmCo/FeCo,针对SmCo/Fe合金研究了球磨时间对其微结构和磁性能的影响,结果表明高能球磨过程不仅将SmCo5粉末转变成非晶合金,还改变了软磁相的成分。探讨了热退火过程中的两种成分非晶合金中硬磁相的演变过程,对于SmCo/Fe非晶合金,在退火温度上升到700℃的过程中,首先SmCo5相和SmCo7相从非晶基体中顺序析出,然后SmCo5相在一个较高的温度下转变为SmCo7相。SmCo/FeCo非晶合金具有完全不同的相变过程,在退火温度上升到700℃的过程中,只有SmCo7相析出。进一步研究了SmCo/FeCo非晶合金的形核与生长激活能和生长激活体积,结果表明,预存的α-(Fe,Co)的生长激活能小于新生成的SmCo7纳米晶的形核与生长激活能,揭示了在Sm Co7/α-(Fe,Co)纳米复合永磁材料中软磁相晶粒容易长大的原因;α-(Fe,Co)和SmCo7的生长激活体积分别为ΔVg*=0.67Ω和ΔVg*=0.99Ω(Ω为部分晶化非晶合金的平均原子体积),结果表明α-(Fe,Co)和SmCo7的生长过程是受热空位辅助扩散实现的。采用多道次轧制强变形工艺并结合再结晶退火和两步时效处理制备出具有多相多尺度的四元TiZrAlV合金,同时获得了高的强度(~1548MPa)和塑性(~6.6%)。研究了经过多道次轧制和未经过多道次轧制的TiZrAlV合金分别采用相同热处理方式的微结构演变过程,结果表明经过多道次轧制存储变形能来提高再结晶的形核率和促进相变,从而细化β晶粒和析出高密度α和α″板条是形成多相多尺度结构的关键。研究了该合金的摩擦磨损特性,结果显示其在真空状态的下的耐磨性有了显著提高,耐磨性的提高归因于合金形成多相多尺度结构,同时提高了强度和塑性。采用电塑性轧制这一强变形工艺和热退火制备出前驱物,再通过室温拉伸工艺诱导应力驱动的马氏体相变,在室温下成功制备了晶粒尺寸低于临界值(20nm)的单相纳米晶Ti Ni合金。研究了样品在经过电塑性轧制和热退火工艺过程的微结构演变,结果表明热退火温度越低,采用室温拉伸诱导马氏体相变就越困难。进一步通过研究在不同应力状态下的微结构演变揭示了一种与应力有关的变形行为:随着应力的增加,纳米晶TiNi合金的变形机制从晶界的滑动和晶粒的转动逐渐演变为晶粒的长大并且位错的激活。它对低于临界尺寸的纳米晶材料的变形机制提出了一种新的见解:采用机械驱动晶粒生长和激活位错运动的思路来提高纳米晶材料的塑性。
[Abstract]:The strong deformation of the metal material under external force is made by strong deformation technology, which makes it in high energy state, which provides great space for the micro structure of the material. After the subsequent heat treatment to release the energy, it is possible to obtain the material with special microstructure and low energy state, and present it with no strong deformation processing completely. Different structures and excellent properties are different. However, different strong deformation techniques and subsequent heat treatment processes are required for different material systems. In this paper, SmCo/a- (Fe, Co) nanocomposite permanent magnetic materials, TiZrAlV alloys and TiNi shape memory alloys are studied by high energy ball milling, multipass rolling and electricity, respectively. Three different strong deformation processes of plastic rolling and subsequent heat treatment and stretching were obtained. The two phase nanocrystals, multiphase multiscale structures and single-phase nanocrystalline materials were obtained respectively. X ray diffraction analysis (XRD), transmission electron microanalysis (TEM), differential scanning calorimetry (DSC) and micro force tensile test machine (Instron 5948) were used. The microstructure evolution of the three materials in the process of strong deformation and subsequent heat treatment and stretching was studied, and the mechanism of nanocrystalline formation, mechanical properties and deformation mechanism were discussed for different materials, and two kinds of amorphous alloy SmCo/Fe and SmCo/FeCo were prepared by high energy ball milling technology. The effect of ball milling time on the microstructure and magnetic properties of SmCo/Fe alloy is studied. The results show that the high energy ball milling process not only transforms the SmCo5 powder into the amorphous alloy, but also changes the composition of the soft magnetic phase. The evolution process of the hard magnetic phase in the two amorphous alloys in the thermal annealing process is discussed, and the annealing temperature for the SmCo/Fe amorphous alloy in the annealing process is in the annealing temperature. In the process of increasing to 700 degrees C, first SmCo5 phase and SmCo7 phase precipitate from amorphous matrix, and then SmCo5 phase transition to SmCo7 phase.SmCo/FeCo amorphous alloy at a higher temperature has completely different phase transition process. In the process of annealing temperature to 700 C, only SmCo7 phase precipitates. Further study of SmCo/FeCo amorphous alloys. The nucleation and growth activation energy and the growth activation volume of the alloy show that the activation energy of the deposited alpha (Fe, Co) is less than the nucleation and growth activation energy of the newly generated SmCo7 nanocrystals, and reveals the reason that the soft magnetic phase grain is easy to grow in the Sm Co7/ - (Fe, Co) nanocomposite permanent magnetic material; the growth activation volume of alpha (Fe, Co) and SmCo7 The results show that the growth process of alpha (Fe, Co) and SmCo7 is realized by the auxiliary diffusion of the heated vacancy, respectively. The growth process of a (Fe, Co) and SmCo7 is achieved by the auxiliary diffusion of the heated vacancy. The multiphase and multi scale four element TiZrAlV is prepared by the multi pass rolling strong deformation process combined with the recrystallization annealing and the two step time effect treatment. At the same time, high strength (~1548MPa) and plasticity (~6.6%) were obtained. The microstructural evolution process of TiZrAlV alloy after multi pass rolling and non multipass rolling was studied by the same heat treatment. The results showed that the nucleation rate and phase transition of recrystallization were improved by multi pass rolling storage deformation. The key to the formation of multiphase and multiscale structure is beta grain and precipitation of high density alpha and "alpha" plate. The friction and wear characteristics of the alloy are studied. The results show that the wear resistance of the alloy is greatly improved under the vacuum state. The increase of wear resistance is attributed to the formation of multiphase multi-scale structure of the alloy, and the strength and plasticity of the alloy are increased at the same time. The electro plastic rolling is used. A single phase nanocrystalline Ti Ni alloy with grain size below critical value (20nm) was prepared at room temperature by using this strong deformation process and thermal annealing to induce the stress driven martensitic transformation. The microstructure evolution of the sample in the process of electro plastic rolling and thermal annealing was studied. It is shown that the lower the thermal annealing temperature is, the more difficult it is to use the tensile induced martensitic transformation at room temperature. Further, the deformation behavior related to the stress is revealed by studying the microstructure evolution under different stress states. With the increase of stress, the deformation mechanism of nanocrystalline TiNi alloy gradually evolves from grain boundary sliding and grain rotation to crystal. The growth of grain and the activation of dislocation. It presents a new view on the deformation mechanism of nanocrystalline materials below the critical size: the idea of mechanically driving grain growth and activating dislocation motion to improve the plasticity of nanocrystalline materials.

【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG339

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