Effect of Boron and Carbon Addition on the Phase Transformations during High-Energy Ball Milling and Subsequent Sintering of Si3N4+B and Si3N4+C Powder Mixtures
This study reports on effect of boron and carbon addition on the phase transformations during ball milling and subsequent sintering of Si3N4+B and Si3N4+C powder mixtures. Ball milling at room temperature was conducted using stainless steel vials (225 mL) and balls (19mm diameter), 300 rpm and a bal-to-powder weight ratio of 10:1. The as-milled powders were uniaxially compacted in order to obtain cylinder samples with 10 mm diameter, which were subsequently sintered under nitrogen atmosphere at 1500°C for 1h. Characterization of the as-milled powders and sintered samples was performed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Only peaks of Si3N4 were identified in X-ray diffractograms of as-milled Si3N4+B and Si3N4+C powders, suggesting that metastable structures were found during milling. After sintering at 1500°C for 1h, the Si3N4+BN and Si3N4+SiC ceramic composites were formed from the mechanically alloyed Si3N4+B and Si3N4+C powders.