Approaching theoretical strength in aluminum alloys via directional heterogeneous nanostructured design

Abstract

Strengthening a material to its theoretical limit is the unremitting pursuit in the field of materials science and engineering. However, it remains extremely difficult for polycrystalline alloys to reach the theoretical limit using conventional strengthening methods. Here, we propose a directional heterogeneous nanostructured strategy (DHNS) to develop super-strong metallic materials. Based on the microstructural strategy, an aluminum-titanium alloy was developed with a yield strength up to ∼3.9 GPa approaching the theoretical limit (G/τY∼22) and a record-breaking specific strength (∼1219 KNm/kg) among metals and alloys. Microstructural characterizations showed that the DHNS alloy mainly consists of directional nanoscale columnar fcc-Al crystals surrounded by nanosized stripe amorphous phases. The columnar crystals are shown to be in hard orientation and defect free, behaving crystalline whisker-like properties. The synergistic effect of hard-orientation nano-colunmar crystals and strong nanoscale amorphous phases renders the initiation of plastic flow difficult, eventually leading to the ultrahigh yield strength of the alloy. The DHNS strategy provides a facile and effective method for developing strong metallic materials especially for fcc-type alloys where slip systems are easy to be activated.