Compacts of TiB, with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of S i c was very effective in improving the sinterability of TiB,. The oxygen content of the raw TiB, powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO, and B,O,. Using vacuum sintering at 1700°C under 13-0.013 Pa, TiB, samples containing 2.5 wt% S i c achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that S i c reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, 0, and Ti, and X-ray diffraction showed the reaction to be TiO, + S i c + SiO, + TIC. Therefore, the improved sinterability of TiB, resulted from the SiO, liquid phase that was formed during sintering when the raw TiB, powder had 1.5 wt% oxygen.
The effects of spherically-shaped filler particles on bending strength, bending elastic modulus, and fracture toughness of resin composites were studied. The filler content was changed by 0, 20, 40, 60, and 70 wt%. Bending properties and fracture toughnesses were determined on three-point bending specimens. Acoustic Emission (AE), i.e., the elastic wave released from a localized source in the material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Detected acoustic emission signals were analyzed for parameters such as amplitude, events, and locations. The fractured surface was examined by a scanning electron microscope. The bending strength and the fracture toughness showed almost the same trend in their increasing rates by filler content, but the elastic modulus showed a much higher increasing rate. A microfracture mechanism of the dental resin composites containing spherically-shaped filler particles is proposed based on the results obtained from the AE-releasing pattern, two-dimensional AE location, and fracture surface findings. In addition to the toughening effects of crack pinning and crack branching, which are observed in the usual commercial resin composites, crack-deflecting effects are confirmed in this new type of dental resin composites.
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