In-situ Synthesis of TiAl Matrix Composites by Combustion Process.

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A combustion reaction synthesis and self-propagating high-temperature synthesis (SHS) using the chemical reaction among elemental powders has been utilized for preparing ceramics and intermetallics. Recently, many attentions are focusing on synthesizing of ceramic matrix and intermetallic matrix composites by mean of this process. The aims of this study is to evaluate microstructures and properties of TiAl matrix composites reinforced with Ti2ALC or TiB2 for light-weight and high-temperature material prepared by the combustion reaction process, following arc melting or HIP reactive sintering.The composite formed by the combustion reaciton from Ti, Al, C powder mixture had a matrix of two phase γ+α2 (lamellar structure), reinforcement particulate Ti2AlC, and some porosity. Subsequent arc melting retained the matrix and reinforcement as before with significant reduction in porosity. In as cast specimens, reinforcement Ti2AlC particles are uniformly distributed in the matrix TiAl (〜30μm). … More The particles are rod-like in shape with sizes 5-15μm in length, and the aspect ratio is estimated to be about 5-10. While, such lamellar structure is not observed in the homogenized specimens. Instead, smaller particles with sizes of 0.5μm in diameter are visible. The strength of the composite both ambient and elevated temperatures clearly increased by the dispersion of reinforcement of Ti2AlC to about 800MPa at ambient temperature and about 400MPa at 1173K, respectively. Also, these composites have 0.9% ductility in bending test. Furthermore, fracture toughness value 14.0MPamィイD21/2ィエD2 is obtained for homogenized specimens.On the other hand, dual structure consisting of γand α2 grains were excited and small TiB2 particles less than 1μm were distributed in the matrix of as HIPed specimens produced from Ti-Al-B powders. However, duplex structure with newly precipitated TiB2 particles around the grain boundaries were occasionally visible in the matrix of homogenized TiAl/TiB2 composites. Those composites possessed bending strength of 700MPa, bending strain of 0/3% and fracture toughness of 15 MpamィイD11/2ィエD1, respectively. Less