The semi-solid powder forming (SSPF) as a promising technology has a complicated process, but the formation mechanism of that remains unclear. The study of semi-solid compression of porous materials is an effective method to investigate the SSPF. Based on analyzing the influence of deformation strain, temperature, strain rate and initial relative density on microstructure evolution and relative density development of sintered porous 2024 aluminum alloy during semi-solid compression, the deformation mechanism and densification mechanism of semi-solid porous materials were proposed. The results show that main deformation mechanisms of porous materials during semi-solid compression are breakup of the solid skeleton or powders, and flowing of liquid with powders or fragments. Breakup mechanism is dominant at center area, whereas flowing mechanism dominates at the margin. With increasing strain and temperature and decreasing strain rate, breakup mechanism becomes primary. The densification mechanisms of porous materials during semi-solid compression are rearrangement of powders or fragments and filling of liquid, resulting from collapse of the solid skeleton or powders and flowing of liquid. The emergence of pores and densification occur simultaneously during semi-solid compression of porous materials.

In-situ synthesis, microstructure, and mechanical properties of four TiB₂-Reinforced Fe-Cr-Mn-Al Steel Matrix Composites have been researched in this work. The microstructure and phases of the prepared specimens have been characterized by using scanning electron microscopy (SEM), X-ray diffraction technique, and transmission electron microscopy (TEM). The sintered specimens consisted of Fe₂AlCr, CrFeB-type boride, and TiB₂. The mechanical properties, such as hardness and compression strength at room temperature (RT) and at elevated temperatures (600 °C and 800 °C) have been evaluated. The compressive strength and Vickers hardness of the sintered specimens increase with the volume fraction of TiB₂ in the matrix, which are all much higher than those of the ex-situ TiB₂/Fe-15Cr-20Mn-8Al composites and the reported TiB₂/Fe-Cr composites with the same volume fraction of TiB₂. The highest Vickers hardness and compressive strength at room temperature are 1213 ± 35 HV and 3500 ± 20 MPa, respectively. As the testing temperature increases to 600 °C, or even 800 °C, these composites still show relatively high compressive strength. Precipitation strengthening of CrFeB and in-situ synthesis of TiB₂ as well as nanocrystalline microstructure produced by the combination of mechanical alloying (MA) and spark plasma sintering (SPS) can account for the high Vickers hardness and compressive strength.