Bend Testing of Forged Al₆₆Ti₂₅Cr₉

Abstract

Several recent reports on the mechanical behavior of polycrystalline L1₂ trialuminides, particularly those based on the ternary Al-Ti-Cr and Al-Ti-Mn systems, have indicated limited tensile ductility at low temperatures (≤623K) as measured in uniaxial tension or in three- and four-point bending. While plastic elongation in bending and in uniaxial tension was not observed for forged Al₆₆Ti₂₅Cr₉ at and below 473K, some room temperature ductility was reported in bending for this compound in the cast and HIPed as well as in the extruded and annealed conditions. This study attempts to understand this discrepancy by subjecting the forged compound to a variety of heat treatments that influence the residual dislocation content and the grain size, and then evaluating bend specimens at 473K. After identifying the heat treatment that provided the maximum ductility, a second set of bend specimens were heat treated and tested at 473K as a function of strain rate (crosshead speed). All bend tests were conducted in air. Bend specimens that were optimally heat treated were also tested at 473K at a slow strain rate in diffusion pump oil to isolate the possible role of environment on ductility. Notched bend specimens were independently tested in the as-forged condition as a function of temperature to obtain a measure of fracture toughness.