Symbiotically engineered crystalline-amorphous nanostructure in a strong-yet-stable Al alloy with large twinning-induced plasticity

Abstract

<p>High performance structural materials with combinations of excellent yet often mutually exclusive properties such as high yield strength, ductility and thermal stability are primarily accessed by synthesizing heterogeneous microstructures. Age-hardened Al alloys with hierarchical nanoprecipitates manifest a good combination of strength and ductility compared to fully amorphous Al alloys, however their thermal stability is in general low, stem from the fast-diffusion element-driven coarsening of nanoprecipitates at elevated temperature. Utilizing the sluggish-diffusion element Cr in the Al matrix, we propose a novel strategy of architecting symbiotically crystalline-amorphous nanostructure (CANS) endowed with self-assembled Cr segregation at crystalline/amorphous interfaces, to develop thermally stable, ultrastrong and ductile Al alloys. The symbiotic CANS-AlCr alloys with homogeneous twinning-induced plasticity of -15% strains at room temperature have ultrahigh compressive yield strength of -1.75 GPa and outstanding thermal stability up to -623 K, simultaneously superior to the parent nanocrystalline and amorphous Al alloys. The interfacial Cr segregation not only promotes twinninginduced plasticity of crystals but also triggers dynamic elemental partitioning between interfaces and amorphous nanolayers, which is critical to their thermodynamic and mechanical stabilization of symbiotic CANS-AlCr alloys. Our strategy advances efficient creation of hierarchical nanostructure and offers a facile route that is regulated across atomic and nanoscopic scales to achieve desirable materials with diverse-yet-precise performances.</p>