Abstract
Precipitation strengthening has been the basis of physical metallurgy since more than 100 years owing to its excellent strengthening effects. This approach generally employs coherent and nano-sized precipitates, as incoherent precipitates energetically become coarse due to their incompatibility with matrix and provide a negligible strengthening effect or even cause brittleness. Here we propose a shear band-driven dispersion of nano-sized and semicoherent precipitates, which show significant strengthening effects. We add aluminum to a model CoNiV medium-entropy alloy with a face-centered cubic structure to form the L21 Heusler phase with an ordered body-centered cubic structure, as predicted by ab initio calculations. Micro-shear bands act as heterogeneous nucleation sites and generate finely dispersed intragranular precipitates with a semicoherent interface, which leads to a remarkable strength-ductility balance. This work suggests that the structurally dissimilar precipitates, which are generally avoided in conventional alloys, can be a useful design concept in developing high-strength ductile structural materials.
Highlights
Precipitation strengthening has been the basis of physical metallurgy since more than 100 years owing to its excellent strengthening effects
Unceasing endeavors have been exerted in developing multiprincipal element alloys (MPEAs) through precipitation strengthening, and several studies demonstrated that homogenously distributed L12 nanoparticles in a FCC matrix are effective in significantly enhancing strength while retaining moderate ductility[17,18,19,20,21,22]
Our approach demonstrates that structurally dissimilar precipitates, which are generally avoided due to their negligible strengthening or detrimental effect on ductility, can provide a useful design concept for the development of high-strength ductile structural materials
Summary
Precipitation strengthening has been the basis of physical metallurgy since more than 100 years owing to its excellent strengthening effects. To implement our design philosophy and develop ultrastrong alloys with good ductility, we choose an equiatomic ternary Co–Ni–V alloy as a model matrix system This medium-entropy alloy (MEA), as a subclass of multiprincipal element alloys (MPEAs) or highentropy alloys (HEAs) possessing single-phase structure[13,14,15], exhibits great mechanical properties, in particular a yield strength of ~1 GPa, attributed to severe lattice distortion, and a tensile ductility of 38%15. We present a CoNiV-based MEA that can be strengthened through the formation of semicoherent nanoprecipitates and thermomechanical treatments enabling them to disperse homogeneously in the lattice To realize such a material, ~6.25 at% Al is added to form an L21 ordered body-centered-cubic (BCC) phase in a FCC matrix, based on density-functional theory (DFT) calculations. Our approach demonstrates that structurally dissimilar precipitates, which are generally avoided due to their negligible strengthening or detrimental effect on ductility, can provide a useful design concept for the development of high-strength ductile structural materials
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