The tensile properties and serrated flow behavior of a thermomechanically treated CoCrFeNiMn high-entropy alloy
The tensile properties and serrated flow behavior of a thermomechanically treated CoCrFeNiMn high-entropy alloy
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热处理CoCrFeNiMn高熵合金的拉伸性能和锯齿流行为
DOI：
10.1016/j.msea.2017.03.031
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发表时间：
2017-04-06
期刊：
影响因子：
6.4
通讯作者：
Peng, L. M.
中科院分区：
文献类型：
--
作者：
Fu, J. X.;Cao, C. M.;Peng, L. M.
在较宽的温度和应变速率范围内，系统地研究了CoCrFeNiMn单面心立方相高熵合金的锯齿状流动行为。该合金具有优异的抗断裂性能，拉伸伸长率高达56%。随着温度的升高和应变速率的降低，在中温范围内出现了明显的锯齿形，其演化顺序为A -> A+B -> B -> B -> C -> C。初始的小塑性产生了低密度的位错堆积在晶界处，高密度的位错在随后的剧烈变形阶段被缠结形成细胞亚结构。在400和600℃时，经常观察到弯曲和扭位错。随着温度的升高和应变速率的降低，发生锯齿状流动的临界应变降低，表明由于合金的热力学稳定性，存在正常而非反向的波特文勒沙特列（PLC）效应。得到了两个随温度变化的锯齿状流动活化能(Q)。估计的低Q值（116 kJ mol(-1)）表明，在300 ~ 500℃，位错的钉住过程是由管道扩散引起的。相反，在500 ~ 600℃之间，较高的Q值（295 kJ mol(-1)）表明，位错的钉住或解钉住过程是由高熵合金中最缓慢的扩散物质（即Ni）控制的。
Serrated flow behavior of CoCrFeNiMn high entropy alloy with a single face-centered cubic phase was systematically examined over a wide range of temperature and strain rate. The alloy exhibited excellent fracture resistance with RT elongation up to 56%. Prominent serrations occurred at the medium temperature range and evolved in the sequence of A -> A+B -> B -> B -> C -> C with increasing temperature and decreasing strain rate. The initial small plasticity produced low density of dislocations piled up at grain boundaries and high density of dislocations were tangled to form cell substructures during subsequent severe deformation stage. Bowing and kinks of dislocations were frequently observed at 400 and 600 degrees C. The critical strain for the onset of serrated flow decreased with increasing temperature and decreasing strain rate, indicating a normal and not inverse Portevin Le Chatelier (PLC) effect due to the thermodynamic stability of the alloy. Two temperature-dependent values of activation energy for serrated flow (Q) were obtained. The estimated low value (116 kJ mol(-1)) implied that pipe diffusion is responsible for the pinning process of dislocations from 300 to 500 degrees C. In contrast, a higher Q (295 kJ mol(-1)) between 500 and 600 degrees C suggested that the pinning or unpinning process of dislocations is controlled by the most sluggish diffusion species (i.e. Ni) in the high-entropy alloy.