Phase stability is an important topic for high entropy alloys (HEAs), but the understanding to it is very limited. The capability to predict phase stability from fundamental properties of constituent elements would benefit the alloy design greatly. The relationship between phase stability and physicochemical/thermodynamic properties of alloying components in HEAs was studied systematically. The mixing enthalpy is found to be the key factor controlling the formation of solid solutions or compounds. The stability of fcc and bcc solid solutions is well delineated by the valance electron concentration (VEC). The revealing of the effect of the VEC on the phase stability is vitally important for alloy design and for controlling the mechanical behavior of HEAs.

The alloy design for equiatomic multi-component alloys was rationalized by statistically analyzing the atomic size difference, mixing enthalpy, mixing entropy, electronegativity, valence electron concentration among constituent elements in solid solutions forming high entropy alloys and amorphous alloys. Solid solution phases form and only form when the requirements of the atomic size difference, mixing enthalpy and mixing entropy are all met. The most significant difference between the solid solution forming high entropy alloys and bulk metallic glasses lies in the atomic size difference. These rules provide valuable guidance for the future development of high entropy alloys and bulk metallic glasses

Nanoparticle superalloy: Improving the strength of a metal alloy is hard to do without sacrificing the ductility. Yang et al. designed an iron-nickel-cobalt (Fe-Ni-Co) alloy laced with aluminum-titanium (Al-Ti) nanoparticles with both high strength and ductility. The key was getting the composition tuned correctly, because the Fe-Ni-Co matrix reacts with the Al-Ti nanoparticles. This was vital for avoiding environmental embrittlement, enhancing work hardening, and improving ductility. Science , this issue p. 933