MICROHARDNESS AND COMPRESSIVE MECHANICAL-BEHAVIOR OF L1(2) TITANIUM TRIALUMINIDES

Vickers microhardness and compressive mechanical properties of L1(2) Al3Ti + X intermetallics, where X = Cr, Mn, Fe, and Cu, were studied. Compressive tests were carried out at the temperature range from room temperature to 900-degrees-C. At room temperature, both Vickers microhardness and yield strength (0.2 pct offset) decrease with increasing the long-range order parameter S. Essentially the same behavior of yield strength is observed at all compressive test temperatures up to 900-degrees-C. In general, apparent compressive ductility (permanent deformation) increases with increasing test temperature, although with different rates, for most of the alloys, except L1(2) Al3Ti + Mn (high Ti), which is characterized by the lowest long-range order parameter S. Compressive ductility increases with increasing long-range order at all temperatures, but the highest rate of increase occurs at high temperatures above approximately 600-degrees-C and the rate of increase at room temperature is minimal. At low temperatures, deformation-induced microcracks were formed in large numbers in all of the alloys studied, even in the matrix free of preexisting flaws. These microcracks can propagate catastrophically under tensile deformation conditions at a stress level barely approaching 0.2 pct offset prior to the onset of gross plastic flow, leading to a premature fracture. At high temperatures, the initiation of deformation-induced microcracks is inhibited. The mechanical behavior of L1(2) titanium trialuminides is discussed within a general framework of ductile-to-brittle transition.