Achieving superior compressive strength-ductility synergy in a novel ODS-CrFeNi/AlCrFeNi heterostructured high-entropy composite

Abstract

A novel high-entropy heterostructured composite (ODS-CrFeNi/AlCrFeNi) was fabricated by powder metallurgy method. The microstructure and mechanical properties of the composites with various sintering temperatures (950 °C to 1100 °C) and various addition amounts (0% to 20%) of FCC-structured reinforcing phase (ODS-CrFeNi) were investigated. The results revealed a reduction in porosity and an increase in relative density, reaching up to 99% with increasing sintering temperature. The optimal sintering temperature is 1100 °C. In the composites with the addition of 5% and 10% ODS-CrFeNi reinforced phases, spinodal decomposition (SD), forming BCC and B2 phases, takes place both in the matrix and in the reinforcing phase. As the reinforcing phase content is increased to 15% and 20%, SD occurs exclusively in the matrix while is suppressed in the reinforcing phase. The reinforcing phase consists of hard BCC structured Cr rich phases and soft FCC-structured FeNi phases, forming a gradient network structure. The composite with 15% reinforcing phase exhibits high hardness of 841 HV and compressive yield strength, ultimate strength and strain of 6960 MPa, 7690 MPa and 15.5%, respectively, which are 2.5, 2.7 and 1.9 times higher than those of the reference alloys (without reinforcing phase). The excellent strength-ductility synergy originates from the unique gradient network structure formed in the reinforcing phase, i.e. complex heterogeneous structure, which results in hetero-deformation induced (HDI) strengthening for higher strength and HDI strain hardening for higher ductility.