Alloy phase analysis from measurements of bulk magnetic properties
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INTRODUCTION
THE objective of this research was to determine whether bulk magnetic properties can be used to evaluate the microstructure and phase stability of an alloy. The ability to characterize alloy properties and phase stability through correlation with electromagnetic measurements may allow significant improvements in the nondestructive evaluation of advanced alloy properties and the prediction of service life. For example, the aluminum industry would benefit from improved methods of phase determination to assure that desired microstructure and resulting strength exists within the alloy.E~I Empirical studies have shown that in many alloy systems, the electron concentration is the important parameter that influences such factors as the extent of primary solid solubility, the presence or absence of a particular crystallographic structure, the range and stability of intermediate phases, the formation of long-period superlattices, trends in lattice spacings, the number of vacant sites in defect structures, the magnetic susceptibility, and many other qualities.[2] The stability of electron phases, like the stability of the primary solid solutions, appears to be a consequence of interactions between the Fermi surface and the Brillouin zones of these structures, with emphasis on the influence of such interactions upon the density of states at the Fermi surface. As the number of conduction electrons is varied by alloying with constituents of a different valence from that of the solvent matrix, the relative positions of the Fermi surface and zone boundaries are altered. As a result of the change in the relative positions, it is often energetically favorable for the crystal structure to change or for precipitates to form. The metallurgical stability of intermetallic phases as well as some of the mechanical properties in certain alloys have been successfully correlated to electron concentration. Hume-Rothery and Rayno~3~has determined that some intermetallic phases occur at specific electron-to-atom ratios and has called these phases electron compounds. K.A. LINDAHL, Research Engineer, D.L. OLSON, Professor of Metallurgical and Materials Engineering, and J.U. TREFNY, VicePresident of Academic Affairs and Professor of Physics, are with the Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401-1887. Manuscript submitted February 23, 1995. 2958--VOLUME 27A, OCTOBER 1996
Brewert4.5.61has established a relationship between electron concentration and compositional range for a specific crystal structure or phase. Cho t71connected many mechanical properties, including bulk modulus, shear modulus, and Young's modulus to the electron concentration and thus to the Fermi energy. In an attempt to nondestructively determine the properties of materials, electrical and magnetic measurements have been conducted on several alloy systems. The correlation between magnetic susceptibility and the precipitation of solute in heat-treatable aluminum alloys has been investigated.IS] Magnetic pha
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