Effect of High Pressures on the Formation of New Compounds in the Al₈₆Ni₂Co₆Gd₆ Alloy

Abstract

Using the X-ray diffraction and electron microscopy methods, the structure and the elemental and phase compositions of hypereutectic alloy Al₈₆Ni₂Co₆Gd₆ (hereinafter, elemental composition in at %) are studied during melt solidification from 1500°C at a rate of 1000 degree/s under high pressures of 3 and 7 GPa. Melt solidification under high pressure leads to a change in the phase composition of the alloy and the formation of an abnormally supersaturated α-Al(Gd) solid solution. The following new phases were synthesized at a pressure of 7 GPa: the Al₃Gd* phase (of the Al₃U type) containing Co and Ni, which has primitive cubic structure cP4/2 with a lattice parameter of a = 4.285 ± 0.002 Å; the Al₈Co₄Gd* phase (of the Al₈Cr₄Gd type), which has tetragonal structure tI26/1 with parameters of a = 8.906 ± 0.003 Å and c = 5.150 ± 0.003 Å. The structure of all obtained samples is homogeneous, densely packed, and finely dispersed, without shrinkage cavities and pores. The average microhardness of the samples is high due to the formation of a solid solution and dispersion strengthening.