Effect of Al Addition on the Pressure Sintering Properties of B<sub>4</sub>C Powder

The effect of Al addition on the pressure sintering (so-called spark plasma sintering, SPS) behavior of B4C powder by transient liquid phase sintering (TLPS) was investigated. First, an accurate sample temperature evaluation in a closed graphite die was performed using elemental standard powders. It was found that as the sintering temperature increased, the measurable die surface temperature exponentially decreased compared to the die internal temperature (i.e., sample temperature) due to thermal radiation. Next, pressure sintering treatment of the mixed powder of B4C containing 5 vol.% Al was performed in vacuum at a constant compressive stress (50 MPa) and heating rate (2 K/s). Although densification due to Al melting was not observed at 933 K, it was found that densification began at temperatures above 1550 K, where the wettability of Al for B4C is improved, and reached the final stage of sintering at approximately 2200 K. As a result, the densification temperature of B4C with Al addition could be shifted to a lower temperature by approximately 250 K compared to B4C without additives. It was suggested that the formation of Al3BC3 between Al and B4C promoted the rearrangement and shape change of B4C particles, resulting in densification at low temperatures.