The effect of scandium on the phase stability of Al sub 3 Nb and Al sub 3 Zr

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:6389156

Nicholson, D M; Schneibel, J H; Shelton, W A ^[1]; Sterne, P ^[2]; Temmerman, W M ^[3]

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1. Oak Ridge National Lab., TN (USA)
2. Lawrence Livermore National Lab., CA (USA)
3. Daresbury Lab. (UK)

A series of Al-25 (Nb,Sc), at. %, and Al-25 (Zr,Sc), at. %, alloy buttons were arc-cast 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 (DO{sub 22}) had to be replaced by Sc in order to obtain the L1{sub 2} structure. In the case of Al{sub 3}Zr much less Sc was required -- the single phase L1{sub 2} composition is approximately Al-16Zr-8Sc. Recent calculations show that once the tetragonality is properly included in the phase stability of the Tri-Aluminide 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., L1{sub 2}, DO{sub 22}, or DO{sub 23}, 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 (LMTO) electronic structure calculations are compared to the rigid band model and checked against the experimentally determined phase boundaries. 5 refs., 5 figs., 1 tab.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: DOE/CE
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6389156
• Report Number(s): CONF-900466-92; ON: DE91002657
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360104* -- Metals & Alloys-- Physical Properties
656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM BASE ALLOYS
CALCULATION METHODS
COHERENT SCATTERING
DIFFRACTION
ELECTRON MICROSCOPY
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY
ENERGY-LEVEL DENSITY
FREE ENERGY
METALS
MICROSCOPY
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SCANDIUM
SCANNING ELECTRON MICROSCOPY
SCATTERING
STABILITY
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
X-RAY DIFFRACTION