Multistage strain hardening facilitated by in-situ TiO(C) nanoparticles in CoCrFeMnNi high entropy nanocomposite subjected to high strain rate compression

Second phase nanoparticles have been notable reinforcements to enhance strength of high entropy alloys based on Orowan mechanism, but their contributions to improving strain hardening ability through facilitating deformation behaviors are still unclear. In this study, an in-situ TiO(C) nanoparticles reinforced CoCrFeMnNi high entropy nanocomposite was fabricated through powder metallurgy routes. The microstructure subjected to high strain rate compression was investigated to elucidate the deformation behaviors facilitated by TiO(C) nanoparticles and the corresponding contributions to strain hardening ability. The results demonstrated that stacking faults and nanotwins were triggered under the sufficient high flow stress facilitated by Orowan mechanism of TiO(C) nanoparticles. It is noted that a FCC to HCP phase transformation was only nucleated adjacent to TiO(C) nanoparticles due to extra stress concentration. These multiple deformation mechanisms including stacking faults, nanotwins and HCP phase transformation led to multistage strain hardening phenomenon, achieving a simultaneous increase of strength and ductility from 1487 MPa and 51.7% to 1735 MPa and 68.2% compared with CoCrFeMnNi high entropy alloy without nanoparticles.