Unusual two-step dealloying mechanism of nanoporous TiVNbMoTa high-entropy alloy during liquid metal dealloying
Unusual two-step dealloying mechanism of nanoporous TiVNbMoTa high-entropy alloy during liquid metal dealloying
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DOI：
10.1016/j.jmrt.2021.08.100
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
S. Joo;I. Okulov;H. Kato
中科院分区：
文献类型：
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作者：
S. Joo;I. Okulov;H. Kato
在这项研究中，使用液态金属脱合金 (LMD) 从 (TiVNbMoTa)25Ni75 铸态前体合金合成了 3D 互连纳米孔 (3DNP) TiVNbMoTa HEA。铸态前驱体表现出由offcc和hcp相组成的初始枝晶微观结构。在 600°C 下 1 小时后，均匀地合成了厚度约为 10 nm 的微小韧带。在 900°C 时，原始前体合金强烈发生体相转变。具体来说，原始相的枝晶形貌消失，并且offcc相的分数从63%下降到20%。这种预转变行为显着影响脱合金机制。 Kurdjumov-Sachs 方向关系 (OR) 控制先前 fcc 阶段的韧带形成，而 Pitsch-Schrader (P-S) OR 控制先前 hcp 阶段的韧带演化。当反应前沿的脱合金速率降低时，在 fcc 相区域观察到一种不寻常的两步脱合金机制。 Ni 的溶解通过逐步转变 offcc=>hcp=>bcc 发生。先前的fcc颗粒转变为异常大的hcpligaments和微小的bccligments。然后，在 P-S OR 后，异常的 hcp 韧带进一步脱合金为较小的 bcc 韧带。这项研究为通过脱合金设计具有定制形态和先进物理性能的成分复杂的多孔材料铺平了道路。
In this study, 3D interconnected nanoporous (3DNP) TiVNbMoTa HEAs were synthesized from the (TiVNbMoTa)25Ni75as-cast precursor alloy using the liquid metal dealloying (LMD). The as-cast precursor demonstrated the initial dendritic microstructure consisting offccandhcpphases. At 600 °C after 1 h, tiny ligaments about 10 nm thickness were homogeneously synthesized. At 900 °C, the bulk transformation intensively took place at the original precursor alloy. Specifically, the dendritic morphology of the original phases disappeared, and the fraction offccphase decreased from 63% to 20%. This pre-transformation behavior significantly influences the dealloying mechanism. Kurdjumov–Sachs orientation relationship (OR) governed the ligament formation at the priorfccphase while Pitsch-Schrader (P–S) OR controlled the ligament evolution at the priorhcpphase. An unusual mechanism of two-step dealloying was observed at thefccphase region when the dealloying rate was decreased at the reaction front. The dissolution of Ni occurs by stepwise transformations offcc=>hcp=>bcc. The priorfccgrain was transformed to the abnormally largehcpligaments and tinybccligaments. Then, the abnormalhcpligaments were further dealloyed to smallerbccligaments following the P–S OR. This study pave the way for the design of compositionally complex porous materials with a customized morphology and advanced physical properties by dealloying.