Tensile properties of .GAMMA.-Al2O3-fiber-reinforced Al at room and cryogenic temperatures.

The present paper investigates tensile properties of γ-Al2O3-fiber-reinforced Al at room temperature and at cryogenic temperatures. Tensile tests of the metal-matrix composite at cryogenic temperatures were carried out by immersing specimens in liquid nitrogen and in liquid helium. During these tests, the deformation behavior of the specimens was monitored by strain gages of foil types. Stress-strain curves of the composite were composed of two nearly straight lines, which reflect earlier onset to plastic deformation in Al matrix, and implied that γ-Al2O3 fibers were deformed elastically until the specimens were finally fractured at a strain level of approximately 0.6%. The fracture stress, the elongation, and Young's modulus of the composite followed two-parameter Weibull distributions. The mean of the fracture stress and that of Young's modulus were linearly increased, whereas that of the elongation was linearly decreased as temperature is lowered ; nevertheless, the temperature dependence of the fracture stress and the elongation of the composite was small compared to other candidate cryogenic metallic materials. Scanning electron micrographs revealed brittle fracture surface of the γ-Al2O3 fibers in contrast with nearly perfect ductile fracture surface of the Al matrix at both room and liquid helium temperatures.