标题: 高熵合金CoCrFeMnNi于高压下相变与机制探讨
Structural Transition in High Entropy Alloy CoCrFeMnNi Subjected to High Pressure
作者: 陈翊闳
黄尔文
Chen, Yi-Hung
Huang, E-Wen
材料科学与工程学系所
关键字: 同步X光绕射;金属与合金;相变;微结构;高熵合金;synchrotron x-ray diffraction;metal and alloys;phase transformation;microstructure;high entropy alloy
公开日期: 2017
摘要: 等莫耳比高熵合金CoCrFeMnNi在常温常压下为单一Face-centered cubic (FCC)相的合金,近期研究相信该高熵合金有低叠差能,低温下因奈米双晶有优秀的机械性质,但未观察到相变现象。本研究利用角度解析式X-光绕射(Angular-dispersive X-ray diffraction ,ADXRD)高压实验,结果发现该高熵合金在7.1GPa时观察到FCC至Hexagonal close packing (HCP)相的高压相变,两相持续共存到实验最大压力20GPa,卸载回常压后仍有残存HCP相,此过程为不可逆高压相变。本研究也计算两相的晶格常数、相比例与半高宽,也确认该高熵合金在高压下非受到静水压力,受到非等向性的压缩,材料在变形中将有对应的织构与滑移系统产生,与文献比对发现高熵合金转为HCP相后的织构分布与锌在高压下的结果相似,确认最终应转变为单一HCP相,最后此研究也对高压相变的机制进行探讨。
An equal-molar CoCrFeMnNi high-entropy alloy has the cubic crystal system of face-centered-cubic (FCC) at room temperature and atmospheric pressure. The recent research believed that the high-entropy has the property of low stacking fault energy, and excellent mechanic property because of the structure of nanocrystalline in low temperature. However, there was no phase-changing observed. This research used Angular-dispersive X-ray Diffraction (ADXRD) under high-pressure, pressurized the CoCrFeMnNi high-entropy alloy system to 20GPa. After analyzing diffraction data, there was phase transformation from FCC to Hexagonal Close Packing (HCP) when the pressure reached 7.1GPa. Both phases existed until the maximum pressure of 20GPa. When the pressure was unloaded to atmospheric pressure, there are remaining HCP-phase in the alloy, which shows the phase transformation is a non-reversible phenomenon. Besides observing phase transformation under high-pressure and the remaining HCP phase, this research will also calculate the lattice constant, ratio and full width at half maximum (FWHM) of both phases. Then, the result of the analysis will be compared with other theses, and to ensure that high-entropy alloy will not be affected by hydrostatic pressure in a high-pressure environment and non-isotropic compression. During the transformation of the material, there was corresponding texture and slip system. After comparison with other thesis, we discovered that when the phase of that alloy was transformed to HCP, the texture distribution is similar with Zine under pressurized. And confirmed the final phase of the alloy should be a uniform single phase. Finally, this research will investigate the phase transformation mechanism under high-pressure environment.
URI: http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT070451556
http://hdl.handle.net/11536/141494
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