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The Effect of Scandium on the Phase Stability of Al3Nb AND Al3Zr

  • D. M. Nicholson (a1), J. H. Schneibel (a1), W. A. Shelton (a1), P. Sterne (a2) and W. M. Temmerman (a3)...

Abstract

A series of Al-25 (Nb,Sc), at.%, and Al-25 (Zr,Sc), at.%, alloy buttons were arccast in argon and homogenized for 2 h in vacuum at temperatures ranging from 1473 to 1573K. X-ray powder-diffraction indicated that almost all the Nb in Al-25 Nb (DO22) had to be replaced by Sc in order to obtain the Ll2 structure. In the case of Al3Zr much less Sc was required - the single phase Ll2 composition is approximately Al16Zr8Sc.

Recent calculations [1,2] show that once the tetragonality is properly included the phase stability of the trialuminide transition-metal binary alloys can be understood in terms of their electronic density of states. The dominating feature is a deep minimum in the density of states just below the major transition metal d-band peak. The exact position of the minimum changes with structure type (i.e., Ll2, DO22, or DO23, and with c/a). The alignment of the Fermi energy with the minimum appears to determine the equilibrium structure. The results of linearized-muffin-tin-orbital [3] (LMTO) electronic structure calculations are compared to the rigid band model and checked against the experimentally determined phase boundaries.

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References

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1. Nicholson, D. M., Temmerman, W. E., Sterne, P. A., Stocks, G. M., and Pettifor, D. G., Proc. of the Materials Research Society 133, 17 (1989).
2. Carlsson, A. E., Meschter, P. J., J. of Materials Research Society 4(5), 1060 (1989).
3. Anderson, O. K., Phys. Rev. B19, 3060 (1975).
4. Heden, L. and Lundquist, B. I., J. Phys. C4, 2064 (1971).
5. Christensen, N. E. and Satpathy, S., Phys. Rev. Lett. 5(6), 600 (1985).

The Effect of Scandium on the Phase Stability of Al3Nb AND Al3Zr

  • D. M. Nicholson (a1), J. H. Schneibel (a1), W. A. Shelton (a1), P. Sterne (a2) and W. M. Temmerman (a3)...

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