具有体心立方结构的碳间隙难熔高熵合金

Interstitially carbon-alloyed refractory high-entropy alloys with a body-centered cubic structure

间隙碳掺杂是改善高熵合金性能的一种有效方法.然而,迄今为止的相关探索局限于具有面心立方结构的高熵合金体系.本文系统研究了难熔高熵合金(Nb_(0.375)Ta_(0.25)Mo_(0.125)W_(0.125)Re_(0.125))_(100−x)Cx(x=0,5.9,11.1,15.8,20)的结构、力学和物理性能.实验结果显示,虽然初始的Nb_(37.5)Ta_(25)Mo_(12.5)W_(12.5)Re_(12.5)高熵合金(x=0)具有体心立方结构的主相和明显的杂相,其体心立方相的比例随着碳含量的增加而增加,并在x为20时接近100%.不仅如此,碳含量的增加导致体心立方晶格的膨胀、韦氏硬度的增强、剩余电阻率的增大,以及费米面附近的态密度的微小变化.所有这些特征与碳原子占据间隙位的预期一致.当碳含量大于或等于11.1时,X射线光电子能谱研究结果表明碳和金属原子间形成化学键,暗示一部分碳原子也可能占据晶格位.此外,半定量分析表明碳原子的引入导致的混合熵增加对稳定(近乎)单相固溶体发挥了关键作用.我们的工作不仅揭示了第一个具有体心立方结构的碳间隙高熵合金系列,而且有助于更好地理解碳在难熔高熵合金中的合金化行为.

The introduction of carbon interstitials into high-entropy alloys(HEAs)provides an effective way to improve their properties.However,all such HEA systems explored so far are limited to those with the face-centered-cubic(fcc)structure.Here we report the structural,mechanical and physical properties of the refractory(Nb_(0.375)Ta_(0.25)Mo_(0.125)W_(0.125)Re_(0.125))_(100−x)C_(x) HEAs over a wide x range of 0≤x≤20.It is found that,whereas the starting HEA(x=0)is composed of a major body-centered-cubic(bcc)phase with significant impurities,the bcc phase fraction increases with the C concentration and achieves almost 100%at x=20.Moreover,the increase of C content x results in an expansion of the bcc lattice,an enhancement of the microhardness,an increase in residual resistivity and a small variation of density of states at the Fermi level.All these features are consistent with the expectation that carbon atoms occupy the interstitial site.For x≥11.1,the X-ray photoelectron spectroscopy indicates the bond formation between the carbon and metal atoms,suggesting that some carbon atoms may also reside in the lattice site.In addition,a semiquantitative analysis shows that the enhanced mixing entropy caused by carbon addition plays a key role in stabilizing the(nearly)single solid-solution phase.Our study not only provides the first series of carbon interstitial HEAs with a bcc structure,but also helps to better understand the alloying behavior of carbon in refractory HEAs.