Nano-Al₂O₃ Reinforced Fe-Cr-Ni Composites Fabricated by Reactive Hot Pressing

Based on low-temperature hot-press sintering and rapid thermit reaction, heat-resistant metal matrix composites with nano-ceramic reinforcement were prepared via reactive hot pressing. According to XRD, the composites comprised predominantly of (fcc) Cr0.19Fe0.7Ni0.11, (fcc) Fe-Cr and alumina at 700°C through the highly-exothermic thermit reaction between the starting powders. Three-point bending strength, fracture toughness, Vickers hardness and relative density increased with the increase of hot-press sintering temperature and holding time. The improving mechanical properties may be explained by increasing of content of (fcc) Cr0.19Fe0.7Ni0.11. SEM analysis showed a microstructure consisting of equiaxial granules at 700°C for 1 h and a uniformly dispersed network of very fine grains at 700°C for 2 h. It is considered that, in the reactive hot-pressing process, Al atoms diffused into the metal matrix (Fe2O3, Cr, Ni) sites and formed Al2O3 and Fe-Cr-Ni matrix. Such a technique offers the possibility of synthesizing heat-resistant metal matrix composites with nano-ceramic reinforcement materials at considerably lower temperature.