Dispersion hardening using amorphous nanoparticles deployed via additive manufacturing

Nanoparticles or precipitates are long used to block dislocations to strengthen metals. However, this strengthening mechanism unavoidably adds stress concentrations at the obstacles, instigating crack initiation that hampers ductility. Here, we demonstrate a strategy that replaces the traditional crystalline dispersions with dense amorphous nanoparticles, which is made possible via laser powder bed fusion. Porosity-free copper-based nanocomposites are demonstrated as a prototype, consisting of densely and uniformly distributed amorphous boron-carbide nanoparticles (~47 nm in average diameter, up to 12% volume fraction) via an in situ nanofragmentation and melt-quench process. The amorphous nanoparticles act as dislocation sinks, thereby alleviating local stress concentration. They also self-harden along with tensile deformation, promoting strain hardening and therefore homogeneous plastic flow. The as-built composite achieves a tensile strength of more than one gigapascal and a total elongation of approximately 10%, more than twice that of its crystalline dispersion counterpart. Defect accumulation is also suppressed upon cyclic deformation of the as-built bulk nanocomposites, delivering a fatigue strength limit (at > 10⁷ cycles) of more than 70% of the tensile strength. Our results demonstrate an effective strategy for additive manufacturing of metallic materials with superior properties.