Production and characterization of boron carbide / boron carbide silicon layered composites by spark plasma sintering

In this study, B4C/B4C-Si functional graded composites heve been produced by adding different volume amount of silicon powder to boron carbide powder on a pure B4C substrate by spark plasma sintering technique. It is preferred to sinter boron carbide with spark plasma system cause of advantages of this system such as sintering at lower temperatures, at lower pressure and accomplishment on materials which are hard to be densified due to their chemical properties. SPS process is basically a modification of hot pressing and the fundamental difference is that high electric current passes directly through the pressing mould and powder compact, whereas a powder compact in a diepunch assembly is heated by external heating source in hot. Typically, the die-punch assembly in hot pressing is heated by external heating with the heating coils being placed around the inner wall of the vacuum chamber. On the contrary, the sample and die in the SPS process are heated by Joule's heating with the current passing partly through die and rest through the powder compact, depending on temperature and thermophysical properties of the powder compact. As far as the characteristics of the starting powders are concerned, conducting powders are heated by Joule effect and by heat transfer from the die-punch, while the nonconductive powders are heated only through the heat transfer from the die-punch. The SPS process utilizes pulsed high DC along with uniaxial pressure to enhance consolidation of powders. During the process, the combination of a low-voltage, high intensity pulsed DC and uniaxial pressure are simultaneously applied, which in turn offers the possibilities of using rapid heating rates and very short holding times to obtain highly dense samples.