Systematic investigation of the microstructure evolution and dynamic recrystallization mechanisms of as-cast Fe–TiB2 composites under different hot deformation parameters

Abstract

Fe–TiB2 composite shows great potential in lightweight materials for automotive parts due to its lightweight, high strength and high specific modulus etc. However, challenges remain with regard to establishing a fine hot working process of Fe–TiB2 composites. Here, a series of isothermal hot compression tests was conducted to systematically investigate the microstructure evolution and the dynamic recrystallization (DRX) mechanisms of as-cast Fe–TiB2 composites at different sets of hot deformation parameters. The results indicate the true stress drops more significantly after reaching its peak at low temperatures compared to high temperatures, since low temperatures favors the DRX through particle stimulated nucleation (PSN) in Fe–TiB2 composites, as featured by layers of DRXed grains surrounding TiB2 particles. Continuous dynamic recrystallization (CDRX) process gradually dominates as strain rate increase from 0.01 s−1 to 1 s−1 in Fe–TiB2 composites hot compressed to the true strain of 0.69 at 900 °C, as evidenced by the presence of DRXed grains with larger size and uniform distribution in matrix. DRX through PSN is the primary DRX mechanism at low temperature and low strain rate, while CDRX dominates the DRX mechanism at high temperature and high strain rate. Both DRX behaviors deepen with the increase of the strain. Different hot deformation parameters favor different DRX mechanisms. The increase in temperature and strain rate leads to a transition of the dominant recrystallization mechanism from the DRX through PSN to CDRX which is attributed to the competition for stored energy between the DRX through PSN and CDRX process.