Copper Content Dependence of the Lattice Parameters of Ti(NiCu)<SUB>2</SUB>

Abstract

The ternary Ti-Ni-Cu system forms a tetragonal Ti(NiCu) 2 phase with C11 b -type structure, in a wide range of copper content. The copper content dependence of the lattice parameters of the Ti(Ni 1-Y Cu Y ) 2 (0.22 ≤ Y ≤ 0.75) alloys and those of the Ti(NiCu)2 precipitate formed in the Ti 49 (Ni 1-X Cu X ) 51 (0.06 ≤ X ≤ 0.4) alloys, were determined by powder X-ray diffraction. The parameters a and c both exhibit a minimum, but the ratio c/a decreases almost linearly as the copper content increases. The coherency between the matrix and the precipitate becomes worse as the copper content increases. The relation between the copper contents X and Y will be approximated as Y = 1.24X + 0.09. While the X-ray diffraction patterns can be indexed by the C11 b -type structure, diffuse 1/2{110} reflections appear in the electron diffraction pattern. The Vickers microhardness of Ti(NiCu) 2 decreases as the copper content increases.