Overcoming the strength-ductility trade-off of an aluminum matrix composite by novel core-shell structured reinforcing particulates

Abstract

The trade-off between strength and ductility of particulate reinforced metal matrix composites (PRMMCs) has been a longstanding puzzle. Here we propose an effective strategy to surmount the inverse relationship between strength and ductility of an A356 Al alloy based PRMMC by in situ synthesizing novel reinforcing particulates with a special core-shell (CS) structure. Such structure features a Ti core inside a dual-layer shell: the inner layer has a nano-grained (~130 nm) heterogeneous structure, and the outer layer possesses a composite structure composed of a (Al,Si)3Ti substrate with dense dispersion of nanoparticles. As a result, the obtained composite reinforced with such CS reinforcing particulates (CS composite) achieves an unprecedented tensile elongation to failure of 8.3 ± 0.8% and a uniform elongation of 7.1 ± 0.6%, which nearly triples that of the same alloy based composite reinforced with monolithic (Al,Si)3Ti particulates (monolithic composite) and equivalent to corresponding matrix alloy while maintaining high ultimate tensile strength of 373 ± 8.8 MPa and yield strength of 268 ± 7.9 MPa, equivalent to monolithic composite simultaneously. This special architecture of shell renders itself a high capability of stress bearing and good toughness, and the nanoparticles in outer layer further slower crack development, which significantly postpone crack formation in shell. Subsequent propagation of cracks in Ti core is also constrained remarkably by the transformation-induced plasticity effect occurred ahead of crack tips resulting from stress-induced phase transformation of hcp-Ti into fcc-Ti. These factors lead to highest work hardening rate that undergoes a long plateau and thus overcome the strength-ductility trade-off of A356 alloy based PRMMC.