【作者】 刘雄军；

【Author】 Liu Xiongjun;University of Science & Technology Beijing;

【机构】 北京科技大学；

【摘要】 高熵非晶合金是兼具高熵合金多主元的成分特征和非晶合金长程无序的原子结构堆垛特性的一种新型无序合金。自从高熵非晶合金被发现以来就引起了广泛的关注。然而,高熵非晶合金的内在结构本质及其优异性能的来源仍缺乏研究。本报告将主要介绍近来我们课题组在高熵非晶合金的玻璃转变行为方面的研究工作。(1)高熵非晶的形成能力:传统非晶合金的设计中,合金化是提高非晶形成能力(GFA)的有效方法,其实质是利用合金化多组元提高合金的复杂性(即:"混乱法则")。高熵非晶由于其多主元(至少5元)、等原子比(或近原子等比)的成分特征,具有高混合熵的特点。依据"混乱法则",高熵效应有利于非晶结构的形成。然而,研究发现高熵非晶相对于传统非晶具有较差的GFA。同时,研究还发现高熵非晶的GFA与其热稳定性之间存在异常关系。(2)高熵非晶合金异常玻璃转变行为:在加热过程中随着玻璃转变的发生,非晶固体转变为过冷液体,非晶态中冻结的平移自由度得到释放,因此非晶态过冷液体的比热通常将增加3R/2(R为气体常数)。然而,研究发现,高熵非晶合金的过冷液体具有异常小的过剩比热容,在玻璃转变过程中其比热值仅增加R/2,以及极其不明显的模量软化行为。进一步结构分析和计算模拟结果表明,高熵非晶合金具有更加均匀且致密的原子堆垛结构,同时高熵效应及缓慢原子扩散效应限制了原子运动,只有较少量的类液态原子发生局部的玻璃转变。更多还原

【Abstract】 High-entropy bulk metallic glasses(HE-BMGs) are a new kind of metallic materials, which simultaneously possess the compositional feature of multi-elements high-entropy alloys and the structural characteristics of amorphous alloys. HE-BMGs have attracted extensive attention due to their unique properties since the first HE-BMG was discovered. However, researches on the nature of atomic structures and structure-properties relationships in HE-BMGs are still lacking. In this talk, we will report our recent work on the glass transition behaviors of HE-BMGs.(1) Poor glass-forming ability(GFA) of HE-BMGs. Alloying is an effective method to improve GFA of traditional MGs. By increasing the complexity of alloys(i.e., "Confusion Principles") is beneficial to improve GFA. In this regard, HE-BMGs which are characterized by multiple principal elements(≥5) with equal or nearly-equal atomic ratio and high-mixing entropy are expected to possess good GFA. However, we found that HE-BMGs have worse GFA compared with respect to their traditional BMG counterparts. Moreover, we revealed an unusual relationship between the GFA and their thermal stability in HE-BMGs.(2) Abnormal glass transition(GT) behavior of HE-BMGs: For conventional MGs, the heat capacity jump was found to be a constant value of 3 R/2(R: gas constant) during GT due to the fact that each atom gains three translational degrees of freedom accompanying with the glass-liquid transition. However, it is found that the supercooled liquids of HE-BMGs exhibit an abnormally ultra-low heat capacity jump(about R/2), and a very inconspicuous modulus softening behavior. Further boson peak and structural analysis coupled with ab initio MD simulations show that the HE-BMGs have a more homogeneous and denser structure with fewer liquid-like atoms involved in GT with respect to traditional BMGs, which results in local GTs in HE-BMGs.更多还原