Microstructure and mechanical behavior of spark plasma sintered TiB2/Fe-15Cr-8Al-20Mn composites

Highlights: • Bulk TiB₂/Fe-15Cr-8Al-20Mn composites have been fabricated by MA and SPS. • CrFeB, Mn₂B and Fe₂AlCr phases form during SPS. • An explanation on the formation of CrFeB-type boride and Fe₂AlCr phase is proposed. • The sintered composites exhibit excellent hardness and compressive strength. Fe-15Cr-8Al-20Mn matrix composites with varying volume fractions of TiB₂ (15–30 vol%) were fabricated by the combination of mechanical alloying (MA) and spark plasma sintering (SPS). The influence of TiB₂ particulate content on the microstructure and mechanical properties of the composites was investigated in detail. Mechanical alloying between metallic elements was almost completed after approximately 30 h of milling, and the final ball milled powders consisted of a supersaturated α-Fe(Cr, Mn, Al) metallic solid solution and TiB₂ ceramic component. Following the sintering process, the sintered composites were composed of Fe₂AlCr, CrFeB-type boride, Mn₂B-type boride and TiB₂. The compressive strength and Vickers hardness of the sintered composites were related to the volume fraction of TiB₂ in the matrix, which are all much higher than those of the reported TiB₂/Fe-Cr composites with the same volume fraction of TiB₂. The highest Vickers hardness and compressive strength at room temperature are 767 ± 18 HV and 2835 ± 21 MPa, respectively. These composites still show relatively high compressive strength as the testing temperature increasing up to 600 °C. The high Vickers hardness and compressive strength were mainly attributed to the precipitation strengthening of CrFeB, Mn₂B and Fe₂AlCr and nanocrystalline microstructure produced by the combine of MA and SPS.