Abstract:The main subject of this work is an investigation of the effects of heating rate and current on the crystallisation of amorphous precursors in spark plasma sintering (SPS). For this, dry gel of Al 2 O 3 -SiO 2 with a molar ratio of 1:1, was synthesized and sintered in-situ by SPS, and also by hot pressing (HP) for comparison. Phase analysis showed that the only crystalline product in both cases was mullite, whose Al 2 O 3 content was lower in the SPS specimens. The microstructures showed a low volume fraction of large mullite fibers in the SPS specimens, whereas a high volume fraction of fine equiaxed grains was present in the HP specimen. The main difference in microstructure between HP and SPS specimens could be explained in terms of the higher heating rate of the SPS specimens. The size of the SPS die also affected the size and aspect ratio of the mullite fibers produced, which might have been due to either the different electrical current required or a difference in specimen temperature profile.

High-entropy alloy of NiCoCrFeMnCuC were made by vacuum non-consumable arc furnace in the present work. The crystal structure of NiCoCrFeMnCuC was analyzed by XRD. The corrosion resistance of NiCoCrFeMnCuC in 10%HNO3-3%HF, 10%H2SO4, 5%HCl and 10%HF was investigated, respectively with weight loss experiment. The results show that main intermetallics of the alloy are CoCx, FeNi3 and Fe3Mn7. The NiCoCrFeMnCuC has simple crystal structures with face-centered cubic crystal structure FCC and Quartet and has excellent corrosion resistance in some medium acid liquids.

A new porous nozzles for refining molten aluminum were made from mullite，graphite powder, red mud and sodium silicate. The relationships between graphite content and permeability, sintering parameters and permeability, graphite content and compressive strength were investigated, respectively. The internal structures of the nozzle before and after sintering were observed by SEM. The experimental results show that the permeability of sample can be improved by sintering at temperature of 1000°C for 2 hours. As graphite content increases, the permeability of sample increases, yet the ultimate compressive strength decreases. The compressive strength can be enhanced by using combination of different sizes of mullite particles.