Al-Cr-Ni-Ti (aluminum-chromium-nickel-titanium)

Abstract

Using starting metals of 99.995% Al, 99.65% Cr, 99.95% Ni, and 99.9% Ti, [1956Tay] inductionor arcmelted about 45 Ni-rich quaternary alloys. The alloys were annealed at 1000 °C for 24 h or at 750 °C for 4 days and quenched in water. The phase equilibria were studied by metallography and x-ray powder diffraction. The pseudoternary sections on the Ni3Al-‘Ni3Cr’-Ni3Ti plane determined by [1956Tay] at 1000 and 750 °C are shown in Fig. 1. The lower boundary of the ( + + Ni3Ti) region was found to be slightly curved, as the sections are not strictly pseudoternary. The L12-type cubic phase Ni3Al ( ) dissolves more than 15 at.% Ti, which substitutes for Al. Ni3Ti (D024-type hexagonal compound denoted by [1956Tay]) is stoichiometric and shows no solubility for Al or Cr. Perspective views of the quaternary phase relationships at 1000 and 750 °C are shown in Fig. 2 [1956Tay]. In addition to the and Ni3Ti phases, NiAl and NiTi (both B2-type cubic) and Ni2AlTi (L21-type cubic) are present. Not all tie-lines and three-phase regions are seen in Fig. 2. The only tie-tetrahedron ( + + Ni3Ti + Ni2TiAl) identified by [1956Tay] is indicated in Fig. 2(b). Using pure metals, [2004Pic] prepared eight quaternary alloys. Four of these had a Ni content of ∼76.5 at.%. The other four had ∼71.5 at.% Ni. The Al, Cr, and Ti contents were in the ranges of 4-10, 5-14, and 5-19 at.%, respectively. The alloys were annealed at 1100 for 16 h or at 1000 °C for 112 h and quenched in water. The phase equilibria were studied with scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy. The phases identified are (fcc), (L12 type cubic), Ni3Ti (D024 type hexagonal), and body-centered cubic (bcc, denoted by [2004Pic]). The experimental data were used to compute the phase equilibria by the CALPHAD method at 1100 and 1000 °C. The computed equilibria showed some additional phases, NiTi or NiAl (B2 type, denoted by [2004Pic]) and Ni2AlTi (L21-type cubic, denoted H by [2004Pic]), in regions where no experimental points were determined. The computed isothermal sections at 1100 °C and at constant Al contents of 76.5 and 71.5 at.% are shown in Fig. 3 and 4, respectively, along with four experimental points in each case. There is general agreement between the experimental results and the computed equilibria, with one or two small differences. The experimental homogeneity range of in Fig. 3 is smaller than the computed range.