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a b s t r a c tThere is increasing interest in both relating the mechanical behavior of high-entropy alloys to their microstructural evolution and in their development for various applications. A special two-day international workshop on the above topic was held in Guiyang, China, in December 2014. The workshop gathered scientists and engineers to exchange information on recent progress in high-entropy alloys, to discuss the scientific issues and challenges to foster international collaborations, and to identify future directions. In this paper, a summary of this workshop is presented, including aspects of definition/terminology, phase formation, microstructure and phase stability, strengthening mechanisms, and hightemperature properties. Future research directions are also outlined. SynopsisThe continued development of high-performance materials is required for increased energy efficiency and sustainability. Traditionally, metallic alloys have been widely applied as structural materials. The conventional alloy design strategy usually is to start with one element as the principal constituent and adding other minor elements for the further optimization of properties and performances. After extensive efforts on these traditional alloys, the development of traditional alloys is approaching its limits. Recently, a new alloy design concept was proposed: the idea is to simultaneously alloy several principal elements (usually !5) to obtain high mixing entropy. As a result, many novel concentrated multicomponent alloys are in the process of being developed [1e6]. In a timely response to this rapid development, a two-day international workshop was held in Guiyang, PRC in December 2014 to exchange information on recent progress, foster international collaborations, and identify future research directions. The main theme of the workshop was the relationship between microstructures and mechanical properties. In this paper, a summary of this special workshop is presented, which includes; 1) Definition/terminology, 2) Main characteristics resulting from multiple primary constituents, 3) Atomic size effects on phase formation, 4) Microstructure and phase stability, 5) Strengthening mechanisms, 6) High-temperature mechanical properties, and 7) Future directions for research Definitions/terminologyAlthough "high-entropy alloys (HEAs)" have now become a new class of materials, the name has not been clearly defined since its inception. This often causes confusion in the scientific community.

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The relaxation spectrum of glassy solids has long been used to probe their dynamic structural features and the fundamental deformation mechanisms. Structurally complicated glasses, such as molecular glasses, often exhibit multiple relaxation processes. By comparison, metallic glasses have a simple atomic structure with dense atomic packing, and their relaxation spectra were commonly found to be simpler than those of molecular glasses. Here we show the compelling evidence obtained across a wide range of temperatures and frequencies from a La-based metallic glass, which clearly shows two peaks of secondary relaxations (fast versus slow) in addition to the primary relaxation peak. The discovery of the unusual fast secondary relaxation unveils the complicated relaxation dynamics in metallic glasses and, more importantly, provides us the clues which help decode the structural features serving as the ‘trigger' of inelasticity on mechanical agitations.

a b s t r a c tWe report on the alloy design strategies, precipitation mechanism and mechanical properties of an ultra-high strength steel hardened by co-precipitation of nanoscale NiAl and Cu particles. The steel, developed through a computational-aided alloy design approach, exhibits a tensile strength of $1.9 GPa, an elongation of $10% and a reduction in area of $40%. Atom probe tomography (APT) reveals an interesting type of co-precipitation mechanism of NiAl and Cu nanoparticles, in which the NiAl particles first come out of the supersaturated solid solution and the rejection of Cu solutes leads to the heterogeneous precipitation of Cu particles adjacent to the NiAl particles. The observed precipitation sequence of ''supersaturated solid solution ? NiAl ? NiAl + Cu'' is substantially different from the one previously reported in Cu-strengthened steels, which involves the process of ''supersaturated solid solution ? Cu ? Cu + NiAl''. The modulation of the precipitation sequence is attributed not only to the relatively high Ni/Cu and Al/Cu ratios but also the synergistic combination of Ni, Al, Mn and Cu additions in the steel. In addition, APT also reveals the precipitation of a small amount of nanoscale Fe 3 (Mo, W) 3 Cand NbC-type carbides. The combination of the strengthening effects from the nanoscale NiAl particles, Cu particles and carbides contributes significantly to the overall ultra-high strength of the steel.