高熵非晶合金形成规律的参数研究

Parametric Study on Amorphous High-Entropy Alloys Formation

高熵合金主要有三种物相,固溶体、金属间化合物和非晶相,之前的研究表明可通过混合焓和拓扑参数来预测具体成份可形成哪种物相,但这些研究所采用的高熵合金成份差异较大,非晶的数量较少,而且也没有考虑到合金的制备过程对成相的影响,更为重要的是这些研究中均采用单质元素的原子半径来计算合金的拓扑结构,而这可能并不合适。本文制备了92个Ti Zr Hf M、Ti Zr Hf MM、Ti Zr Hf MMM (M=Fe,Cr,V,Nb,Al,Ag,Cu,Ni)高熵合金薄带,其中约一半合金形成非晶,构成了一个具有足够数量的且成份变化很窄的高熵合金数据库,以此来验证之前报道的参数能否有效区分晶相(包括固溶体和化合物)和非晶相,结果表明现有的四种拓扑参数均完全无效,这说明采用单质元素的原子半径来计算合金的拓扑结构并不合适。为此提出了一种考虑局域电子环境变化的合金组元原子半径的修正值,采用此修正值计算的拓扑参数在区分晶态和非晶态合金时有效性明显提高。另外,本文还发现合金组元在单质时的晶体结构对合金是否形成非晶具有很大的影响,主要原因是密排六方与面心立方金属元素间的混合焓偏负,而与体心立方元素的混合焓偏正,这一规律不单在本文所用的金属元素中存在,而且在所有金属元素中均存在。本文的结果不仅为高熵合金的参数研究提供了全新的角度,并且还揭示了冶金学、晶体学和原子物理三个领域中几个重要物理量间的潜藏联系。

Chemical and topological parameters have been widely used for predicting the phase selection in high-entropy alloys (HEAs).Nevertheless,previous studies could be faulted due to the small number of available data points,the negligence of kinetic effects,and the insensitivity to small compositional changes.Here in this work,92TiZrHfM,TiZrHfMM,TiZrHfMMM (M =Fe,Cr,V,Nb,Al,Ag,Cu,Ni) HEAs were prepared by melt spinning,to build a reliable and sufficiently large material database to inspect the robustness of previously estabhshed parameters.Modification of atomic radii by considering the change of local electronic environment in alloys,was critically found out to be superior in distinguishing the formation of amorphous and crystalline alloys,when compared to using atomic radii of pure elements in topological parameters.Moreover,crystal structures of alloying element were found to play an important role in the amorphous phase formation,which was then attributed to how alloying hexagonal-close-packed elements and face-centered-cubic or body-centered-cubic elements can affect the mixing enthalpy.Findings from this work not only provide parametric studies for HEAs with new and important perspectives,but also reveal possibly a hidden connection among some important concepts in various fields.