Single-phase concentrated solid-solution alloys (CSA), i.e., alloys without a principle alloying element but one randomly populated crystal structure, exhibit attractive material properties such as very high ductility at cryogenic temperatures, a gentle decrease of strength with temperature, or an unexpectedly high resistance against irradiation. For clarification of those observations assessment of atomic transport mechanisms including formation and migration of equilibrium point defects is indispensable. Positron annihilation lifetime spectroscopy measurements are performed to quantify the concentration of quenched-in thermal vacancies in fcc CSAs after quenching from temperatures close to their onset of melting. For various alloy compositions the concentration of quenched-in vacancies decreases with increasing entropy of mixing $\mathrm{\Delta }{S}_{\mathrm{mix}}$. Whereas alloys with three constituents in nonequimolar fractions (CrFeNi) exhibit vacancy concentrations in the ${10}^{-5}$ range, the studied alloys with four (CoCrFeNi) and five constituents (CoCrFeMnNi, AlCoCrFeNi) do not show a vacancy-specific positron lifetime. Therefore, the concentration of quenched-in vacancies must be in the range of ${10}^{-6}$ or less. It can be concluded that there is either only a vanishingly small fraction of vacancies present at temperatures near the onset of melting or the generated vacancies are inherently unstable.

中文翻译：

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在具有fcc晶体结构的浓固溶合金中寻找空位

单相浓固溶体合金（CSA），即不具有主要合金元素但具有随机填充的晶体结构的合金，具有有吸引力的材料性能，例如在低温下的延展性非常高，强度随温度的降低或出乎意料的高抗辐射性。为了澄清这些观察，必须评估原子输运机制，包括平衡点缺陷的形成和迁移。进行正电子lifetime没寿命光谱测量，以量化从接近其熔化开始温度的淬火后，fcc CSA中淬火的热空位的浓度。对于各种合金成分，淬火空位的浓度随着混合熵的增加而降低$\mathrm{\Delta }{\mathrm{小号}}_{\mathrm{混合}}$。而具有非等摩尔分数（CrFeNi）的三种成分的合金在合金中表现出空位浓度。${10}^{-5}$在此范围内，所研究的具有四种（CoCrFeNi）和五种成分（CoCrFeMnNi，AlCoCrFeNi）的合金没有显示空位比正电子寿命。因此，淬火空位的浓度必须在${10}^{-6}$或更少。可以得出结论，或者在接近熔化开始的温度下仅存在很小一部分的空位，或者所产生的空位本质上是不稳定的。