极端条件下高熵合金组织结构及性能研究

发布时间：2018-01-29 14:22

本文关键词： 高熵合金高压同步辐射变形机制组织结构演化　出处：《燕山大学》2016年博士论文　论文类型：学位论文

【摘要】：高熵合金是近些年发展起来的新型合金,它打破了传统合金设计理念,具有许多优异性能。合金组织结构与稳定性对其性能有着至关重要的影响,因此,对不同结构的高熵合金,在各种条件下研究其组织结构、结构稳定性、以及塑性变形过程中变形机制具有十分重要的理论意义和实际应用价值。本文以高熵合金为研究对象,利用原位高压同步辐射X射线实验技术,研究了高压下不同结构高熵合金的稳定性。面心立方(fcc)的Al0.1CoCrFeNi和体心立方(bcc)的Al3CoCrFeNi高熵合金在30 GPa的压力范围内,都表现出较好的结构稳定性。而密排六方结构(hcp)的稀土HoDyYGdTb高熵合金,在高压下则经历了hcp→Sm-type→dhcp(双层密排六方)→dfcc(扭曲面心立方)的相变过程,相变压力是组成合金的几种单质相变压力的平均值。采用球磨加六面压机高压烧结的方法制备了CoCrFeCuNi和CoCrFeMnNi两种高熵合金,两种合金都具有fcc结构,晶粒尺寸在100 nm左右。在31 GPa压力范围内,保持结构稳定性,体积模量分别为117.5 GPa和136.1 GPa。硬度比相应的铸态样品高很多,分别为494 Hv和587 Hv,CoCrFeCuNi具有相对较高的饱和磁化强度,CoCrFeMnNi饱和磁化强度则比较低,因此,可以通过改变元素控制高熵合金性质。同时,研究了高压退火时Al的添加对Al0.5CoCr CuFeNi和AlCoCrCu FeNi高熵合金组织结构性能的影响。通过高压扭转的方法,研究了高熵合金塑性变形过程。fcc结构高熵合金室温下塑性变形机制包括位错滑移和孪晶,平面位错滑移沿着fcc滑移系:{111}110,孪晶的孪晶面是{111}面,在应变较大时,会产生二次孪晶。而bcc和hcp结构高熵合金主要是通过位错进行。高压扭转后,样品硬度增大,并达到饱和状态,高熵合金都表现出较高的加工硬化率。为了研究冷却速率对高熵合金组织结构的影响,通过甩带法获得了较高的冷却速率,研究了冷却速率对Al0.5CoCrCuFeNi和AlCoCrCuFeNi高熵合金组织结构的影响。结果表明,高冷却速率有效细化高熵合金组织,从粗大的枝晶状组织到细小的等轴组织。同时,高的冷却速率还能有效抑制Cu元素的相分离,提高AlCoCrCuFeNi高熵合金中富铜纳米相的含量,降低其尺寸。冷却速率越高,合金的硬度越大。通过甩带法制备的AlCo CuFeNi高熵合金中,存在大量fcc结构的富铜纳米孪晶相,fcc相与基体B2相之间保持K-S取向关系,{111}fcc∥{110}B2,110fcc∥111B2。退火过程中,纳米孪晶沿着{111}fcc孪晶面方向生长。硬度和弹性模量随着孪晶长大而降低。
[Abstract]:High entropy alloy is a new kind of alloy developed in recent years. It breaks the traditional design concept of alloy and has many excellent properties. The microstructure and stability of the alloy have a vital impact on its properties. The microstructure and structural stability of high entropy alloys with different structures were studied under various conditions. And the deformation mechanism in plastic deformation process has very important theoretical significance and practical application value. In this paper, high-entropy alloy as the research object, in situ high-pressure synchrotron radiation X-ray experimental technology. The stability of high entropy alloys with different structures at high pressure, Al0.1CoCrFeNi and bulk centered cubic (BCC) have been studied. The Al3CoCrFeNi high entropy alloy is in the pressure range of 30 GPa. The rare earth HoDyYGdTb high entropy alloy with dense hexagonal structure has experienced hcp at high pressure. 鈫扴m-type. 鈫扗hcp (double tiered hexagonal). 鈫扵he phase transition process of DFC (twisted face-centered cubic). The phase change pressure is the average value of the phase transition pressure of several kinds of the alloy. Two kinds of high entropy CoCrFeCuNi and CoCrFeMnNi alloys were prepared by ball milling and high pressure sintering with a six-sided press. Both alloys have fcc structure and the grain size is about 100nm. The structure stability is maintained in the pressure range of 31 GPa. The bulk modulus is 117.5 GPa and 136.1 GPA, respectively, and the hardness is much higher than that of the as-cast samples (494Hv and 587Hv, respectively). CoCrFeCuNi has relatively high saturation magnetization and CoCrFeMnNi saturation magnetization is relatively low. Therefore, the properties of high entropy alloys can be controlled by changing the elements. The effect of Al addition on the microstructure and properties of Al0.5CoCr CuFeNi and AlCoCrCu FeNi high entropy alloys during high pressure annealing was studied. The plastic deformation mechanism of high entropy alloy at room temperature including dislocation slip and twin, plane dislocation slip along fcc slip system: {111} 110 has been studied. The twin plane of the twin is {111} plane, which will produce secondary twin when the strain is large. The high entropy alloy of bcc and hcp structure is mainly carried out by dislocation. The hardness of the sample increases after high pressure torsion. In order to study the effect of cooling rate on the microstructure of the high entropy alloy, the high cooling rate was obtained by the strip throwing method. The effect of cooling rate on the microstructure of Al0.5CoCrCuFeNi and AlCoCrCuFeNi high entropy alloys was studied. The results show that the high cooling rate can refine the microstructure of high entropy alloys effectively. At the same time, the high cooling rate can effectively restrain the phase separation of Cu and increase the content of copper-rich nanophase in AlCoCrCuFeNi high-entropy alloy. The higher the cooling rate, the greater the hardness of the alloy. In the AlCo CuFeNi high-entropy alloy prepared by banding method, there are a large number of copper-rich nanocrystalline twinning phases with fcc structure. There is a K-S orientation relationship between the fcc phase and the matrix B2 phase, {111} fcc / {110fcc / 111B2.In the annealing process. The nanotwins grow along the {111} fcc twin plane. The hardness and elastic modulus decrease with the twin growth.
【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】：TG139

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