Design of super-strong and thermally stable nanotwinned Al alloys via solute synergy

Abstract

Al alloys have widespread industrial applications. However, their mechanical strength is often much lower than steels. Here, we investigate the influence of solutes on achieving ultrahigh strength and thermal stability...

Achieving strong and stable nanocrystalline Al alloys through compositional design

“…In contrast to sputtered and electrodeposited NC Al alloys with stable nanograins prior to coarsening temperature, the nanograins and mechanical properties of mechanically alloyed NC Al alloys are sensitive to low and moderate temperatures. NC Al-Fe-Ti underwent recrystallization and mechanical softening as temperature exceeded 400 °C, whereas Al-Ni-Ti coarsened and softened at ~ 250 °C [42]. This strongly suggests that the solute as the grain refiner considerably influences the thermal stability of the NC ternary Al alloys as well.…”

“…An et al showed that Al could effectively refine the grain size of Cu, but the microstructure of Cu-Al alloys coarsened at low homologous temperatures [137,138]. In sputtered Al alloys, Co, Ni and Fe demonstrated astounding ability to refine grain sizes of Al down to less than 10 nm, but Al-Ni, Al-Co and Al-Fe manifested unsatisfactory thermal stabilities [29,35,37,40,42]. Mohjoub et al used first principles calculations to predict general tendency for solute segregation at GBs in Al and found that Sr, Mg, Si and Ca were expected to achieve stable segregated GB state and on the contrary, Ni, Co and Fe are bound to lead to metastable or unstable segregated state due to the formation of stable intermetallic compounds [41].…”

“…Notwithstanding these NC Al-TM alloys endowed with strengths greater than 1.5 GPa, first principles calculations in combination with the NC stability criterion suggest that those Al-TM systems are subjected to very large weighted fraction of unstable segregated GBs, reflective of low propensity for good thermal stability [41]. Indeed, it was found that those NC Al-TM alloys were largely plagued by precipitous softening at low or moderate homologous temperatures upon the intermetallic formations [29,42].…”