Abstract
A multiphase (Mo,Cr)(Si,Al) 2 intermetallic alloy matrix-composite comprising body-centered tetragonal, C11 b (tI6) structured (Mo 0.23 Cr 0.10 )(Si 0.67− x Al x ) and hexagonal, C40 (hP9) structured (Mo 0.16 Cr 0.17 )(Si 0.67− x Al x ) (where x ≤ 0.0008) phases as well as a dispersion of α-Al 2 O 3 and β-SiC phases has been processed by reaction hot pressing of Mo, Si, Al, MoSi 2 and Cr 3 C 2 powders. A noticeable increase could be observed in the hardness of the matrix as well as that of the composite. The indentation cracks follow a more tortuous path and have shorter lengths compared to those in MoSi 2 , although the testing of Single Edge Notch Bend specimens has not shown any improvement in fracture toughness. Oxidation at 1873 K has shown the formation of a scale, containing the crystalline SiO 2 identified as crystoballite, Cr 2 O 3 , α-Al 2 O 3 and Cr 2 MoO 6 phases. With increase in the time of oxidation, a relatively smooth and thick SiO 2 film appears to overlap the other crystalline phases, and cracks develop in the scale due to development of internal stresses during growth of different oxides or cooling to room temperature.
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