H. Izui, Nihon University, Chiba, Japan
Discontinuously reinforced titanium composites containing titanium boride(TiB) whisker are emerging as possible candidate materilals for advanced aerospace applications. Because all of the attractive reinforcements, such as SiC, Al2O3, Si3O4, and B4C, lead to the formation of reaction products at the interfaces. TiB as reinforcement for Ti is the most attractive because of the absence of an intermediate phase between Ti and TiB. The TiB phase provides significant increase in strength and stiffness without increasing density. The coefficient of thermal expansion of TiB is comparable to that of titanium, which eliminates residual stresses at the interfaces between Ti and TiB. A TiB reinforced titanium matrix composite is produced by a cost-effective sintering process called Spark Plasma Sintering (SPS). In the SPS, the pulsed DC current goes through the powder directly. Compared to HIP or hot-pressing(HP) SPS can be consolidated lower temperature and shorter sintering duration. The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) by exploiting the simultaneous TiB whisker formation and the densification occurring during the spark plasma sintering process. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at sintering temperature ranging from 800°C to 1000°C and at sintering duration from 10 min to 50 min. The mechanical properties of TiB whisker-reinforced titanium composite were found to be influenced by the sintering conditions. Tensile specimens of TiB/Ti composites were tested at room temperature, 200, 400, 600, and 800oC. Fatigue tests of the composites were carried out at room temperature and 600oC. The evolution of the composite microstructure, the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.
Summary: A TiB reinforced titanium matrix composite is produced by a cost-effective sintering process called Spark Plasma Sintering (SPS). The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) by exploiting the simultaneous TiB whisker formation and the densification occurring during the spark plasma sintering process. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at sintering temperature ranging from 800C to 1000C and at sintering duration from 10 min to 50 min. The mechanical properties of TiB whisker-reinforced titanium composite were found to be influenced by the sintering conditions. The evolution of the composite microstructure, the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.
