Carbide reinforcement in two directionally solidified alloyed nickel eutectic alloys

Two directionally solidified carbide-reinforced alloyed nicel eutectics were evaluated; an alloy consisting of monocarbide fibers in a single phase matrix and one containing monocarbide fibers in a two-phase γ-γ′ matrix. The mechanical properties and microstructures of these alloys are compared to those of two directionally solified alloys having the same nominal matrix compositions, but not containing carbide fibers. The calculated strengths of the monocarbide fibers in the γ′-containing eutectic alloy are 1,400,000 psi (9650 mn/m²) and 243,000 psi (1680 mn/m²) at room temperature and 1000°C, respectively, while those in the single phase γ matrix eutectic at the same temperatures are 590,000 psi (4060 mn/m²) and 298,000 psi (2050 mn/m²). At room temperature, the lower strength of fibers from the γ matrix alloy is believed to result from stress concentrations induced by the presence of growth facets on the fibers. The lower apparent strength at 1000°C of fibers from the γ′-containing eutectic alloy is related to nucleation of needles believed to be M₂₃C₆ on the monocarbide fibers during deformation. These needles appear to act as stress raisers and cause early failure of fibers.