A new alloy design concept, high-entropy alloys (HEAs), has attracted increasing attentions and becomes a new research highlight recently. Different from traditional alloy design strategy which usually blends with one or two elements as the principal constituent and other minor elements for the further optimization of properties, HEAs are multicomponent alloys containing several principle elements (usually ≥5) in equiatomic or near equiatomic ratio. Due to their unique atomic structure, HEAs possess a lot of distinguished properties. Since the discovery of HEAs, a variety of HEA systems have been developed and shown unique physical, chemical and thermodynamic properties, especially the promising mechanical properties such as high strength and hardness, abrasion resistance, corrosion resistance and softening resistance. Here in this short review manuscript, starting from the research challenges for understanding the deformation mechanism of HEAs, this work briefly summarized the mechanical properties and deformation behavior of HEAs, reviewed the proposed strengthening-toughening strategies and their corresponding deformation mechanism in HEAs. A brief perspective on the research directions of mechanical behavior of HEAs was also proposed.
In recent years, the increasing application demand for Mg alloys in automobile, rail transport, aviation and aerospace industries brings about the growing prominence of seeking reliable techniques to join Mg alloys. As a solid state welding method, friction stir welding (FSW) exhibits unique advantages in joining Mg alloys, and thus arouses widespread research interest. This paper emphatically reviewed the research status of conventional friction stir butt-welding of Mg alloys, and highlighted the welding process, microstructure evolution, texture characteristics, mechanical behavior and their interaction mechanisms. It was indicated that the texture plays a vital role in FSW joint performance of wrought Mg alloys, which is quite different from that in the FSW Al alloy joints. The specific strong texture formed in the weld is the main factor that gives rise to the impediment to achieving equal-strength joints to base materials. At the same time, some focuses like the weldability and the factors that influence joint performance in other types of FSW like lap welding, spot welding and double-sided welding; the weldability, interface bonding mechanism, joint performance and its affecting factors and optimization methods in dissimilar FSW between Mg alloys and other materials like Mg alloys of other grades, Al alloys and steels, were summarized and discussed. Finally, the future research and development directions in FSW of Mg alloys were prospected.
Metallic glasses (MGs) have disordered microstructure and no defects like in crystalline materials and possess a suite of outstanding mechanical and functional properties, showing thus promising potential for wide applications. Due to the lack of long range structural order, it is fraught with difficulties to construct the structure-property relationship in amorphous materials. The study of relaxation dynamics provides a very important approach to understand MGs, and is vital to understand their stability and deformation behavior and remains a core issue in the field of condensed matter physics and materials science. In recent years, with the use of more advanced research methods and the deepening of research, it was found that there exists rich dynamics covered by the extremely wide time scale and the different length scales of glassy state. Different dynamic modes not only correlate with each other but also show distinction. This article reviews recent progress in the study of relaxation dynamics in MGs, and its role in understanding and modifying material properties and optimizing material preparation.