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Phase Diagram Evaluations: Section II

Al-C-Co-Fe (Aluminum-Carbon-Cobalt-Iron) V. Raghavan

Recently, [2006Mar] measured the shift in the Co3AlCx homogeneity region with the addition of Fe up to 3 at.% and the corresponding change in the Seebeck coefficient.

Quaternary Phase Equilbria An update of the Al-C-Co ternary system appears in this issue. With starting materials of high purity Co, Al4C3, C and Fe, [2006Mar] arc-melted under Ar atm three groups of four quaternary alloys each, containing 0.5, 1 and 3 at.% Fe respectively. All compositions were in the region of the Co3AlCx (j) phase, with Fe substituting for Co. The alloys were annealed at 1200 °C for 72 h and furnace cooled. The phases were examined by x-ray diffraction, scanning electron metallography and energy dispersive x-ray analysis. In Fig. 1, the homogeneity region of the j phase in the ternary alloys is compared with the region in the quaternary alloys. The j region in the quaternary alloys is larger and shifted somewhat to lower Al contents. The effect of increasing Fe from 0.5 to 3 at.% on the j region appears small. At 600 °C, the Seebeck coefficient for Co3AlC0.67 is 23.3 lV per K and increases to 32.6 lV per K at Co3.506Fe0.025AlC0.77.

Reference Fig. 1 Al-C-Co-Fe homogeneity range of ternary Co3AlCx (j) (shaded), compared with the same in Fe-containing quaternary alloys [2006Mar]

2006Mar: T. Maruoka and R.O. Suzuki, The Phase Equilibria and Seebeck Coefficient of (Co,M)3AlC (M = Fe or Ni), Mater. Trans., 2006, 47(6), p 1422-1427

Journal of Phase Equilibria and Diffusion Vol. 29 No. 1 2008

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