A mechanistic interpretation of the strength-ductility trade-off and synergy in lamellar microstructures

Abstract

Among various mechanisms responsible for the strength-ductility trade-off in metallic materials, the leading strategy is to delay the onset of necking by improving the work hardening rate via a number of metallurgical approaches such as heterogeneous or gradient microstructures. Recent research activities on high-entropy alloys also witness a wide range of alloy design capabilities that permit these microstructural designs such as the dual-phase lamellar microstructures. This work addresses the contrasting strength-ductility behavior of equiaxed and lamellar microstructures when geometric features are the only tuning parameter. It is found that failures in lamellae are preceded by necking in the hard phase, the growth of which is significantly confined and suppressed by the surrounding soft phase. Detailed finite element simulations reveal various degrees of strength-ductility trade-off and synergy, which mainly depend on the microscopic processes that govern the delayed neck growth and ductile fracture. The upper limit of tensile ductility is theoretically believed to be determined by short-wavelength necking in the hard phase.

Keywords

• Strength-ductility relationship
• Lamellae
• Necking
• Ductile fracture