Dual hetero-structured Ti composites by manipulating self-assembled powder embedded with nano-reinforcements

Abstract

Traditional discontinuously micro-reinforced titanium matrix composites (DRTMCs) produced by casting or forging, are usually confronted with the strength-ductility trade-off dilemma. Their micro-scale reinforcements easily cause incompatible deformation and stress localization. Novel self-assembled composite powder embedding nano-reinforcements paired with additive manufacturing technology has great potential to address this dilemma. Here, we report a special dual-heterogeneous structure with micro-scale networks and grain size gradients. It bespoke exciting strength-ductility synergy and excellent uniform elongation surpassing the as-deposited Ti6Al4V alloy by 32 %, while manifesting a steadier strain hardening behavior. Primarily, alternating basal <a> and pyramidal <a> slips together with substantial pyramidal <c+a> slips induced by hetero-interfaces significantly improved the uniform deformation ability. Then geometrically necessary dislocation (GNDs) and long-range back stress induced by strain inhomogeneity remarkably enhanced the strain hardening ability. This work firstly determined the most preferred orientation relationship (OR) (58.91°/ ${\left[010\right]}_{TiB}$) between TiB_w and the adjoining α-Ti in as-deposited composites. These interfaces showed higher interface strength (16.42 GPa) than those with the most preferred OR of 0°/ ${\left[010\right]}_{TiB}$ in as-forged TMCs, making more contributions to promoting the load bearing capacity of TiB_w. It provided scientific guidance for in-situ synthesizing heterogeneous structures with attractive mechanical properties in Ti composites.