A novel ODS high-entropy composite with improved strength and ductility

Body-centered cubic (BCC) structured high-entropy alloys (HEAs) usually exhibit excellent strength, thermal stability, irradiation tolerance and corrosion resistance but low ductility. In this study, a novel oxide dispersion strengthened (ODS) AlCrFeNi high entropy composite (with BCC-structure reinforced by face-centered cubic (FCC) ODS-CoCrFeNiMn HEA reinforcement was designed and prepared by mechanical alloying and spark plasma sintering. The effects of sintering temperatures (950 °C, 1000 °C, 1050 °C and 1100 °C) and reinforcement amount (5%, 10%,15% and 20%) on microstructure and mechanical properties were investigated. The results showed that the optimal sintering temperature of the ODS AlCrFeNi composites is 1100 °C. The hardness decreases with the increase of the reinforcement content (from 5% to 20%). Compared to the reference alloy (RA) without the addition of reinforcement, the compressive strain of the composite with 15% reinforcement (B–15%F) increases significantly from 8% (RA) to 18%, while the compressive strength increases from 2823 MPa (RA) to 3078 MPa. The B–15%F is composed of matrix, reinforcement and intermediate transition regions. The thickness of transition regions increases with increasing sintering temperature. The matrix consists of fine BCC FeCr phase and B2 NiAl phase, due to spinodal decomposition, together with high-density nanoscale oxides Y4Zr3O12 and a small amount of Y–Al–O. Surprisingly, the crystal structure of reinforcement transforms from FCC into the BCC during SPS. Meanwhile, the mutual diffusion of Al elements in the matrix and Co and Mn elements in the reinforcement also results in similar spinodal decomposition in the reinforcement. The domain size of spinodal decomposition in the reinforcement is coarser than that in the matrix. The reinforcement is mainly distributed on the prior particle boundaries (PPBs), which can effectively reduce/suppress the formation and propagation of micro-cracks along the PPBs, and thus improve both the strength and ductility of the composite.