J.J. Kai

Nanoscale Structural Evolution and Anomalous Mechanical Response of Nanoglasses by Cryogenic Thermal Cycling

One of the central themes in the amorphous materials research is to understand the nanoscale structural responses to mechanical and thermal agitations, the decoding of which is expected to provide new insights into the complex amorphous structural-property relationship. For common metallic glasses, their inherent atomic structural inhomogeneities can be rejuvenated and amplified by cryogenic thermal cycling, thus can be decoded from their responses to mechanical and thermal agitations. Here, we reported an anomalous mechanical response of a new kind of metallic glass (nanoglass) with nanoscale interface structures to cryogenic thermal cycling. As compared to those metallic glasses by liquid quenching, the Sc75Fe25 (at. %) nanoglass exhibits a decrease in the Youngs modulus but a significant increase in the yield strength after cryogenic cycling treatments. The abnormal mechanical property change can be attributed to the complex atomic rearrangements at the short- and medium- range orders due to the intrinsic nonuniformity of the nanoglass architecture. The present work gives a new route for designing high-performance metallic glassy materials by manipulating their atomic structures and helps for understanding the complex atomic structure-property relationship in amorphous materials.

Ductilizing brittle high-entropy alloys via tailoring valence electron concentrations of precipitates by controlled elemental partitioning

ABSTRACT High-strength high-entropy alloys (HEAs) reinforced by hard intermetallics generally show a propensity for embrittlement, significantly undercutting their applications. Here we report a strategy to intrinsically toughen strong-yet-brittle HEAs via altering the valence electron concentration (VEC) of precipitates. It was found that a decrease of the VEC of precipitates by Co substitution for Ni atoms effectively destabilizes the brittle hexagonal-ordered precipitate and promotes the formation of ductile cubic-ordered nano-precipitates in Ni–Co–Fe–Cr–Ti system. Benefiting from such a transformation, a fivefold enhancement of tensile elongation (from 7% to 35%) was successfully achieved together with a simultaneously improved strength up to ∼1.35u2009GPa. GRAPHICAL ABSTRACT IMPACT STATEMENT An effective VEC strategy is proposed to optimize the precipitation behaviors in high-entropy alloys systems. High strength and large ductility are simultaneously achieved in the resultant alloys.