THEORETICAL CONSIDERATION OF SOLID SOLUBI LITY AND FORMATION OF COMPOUNDS IN FE ALLOYS BY EXTENDED HUCKEL-METHOD

In the present work the solid solubility, compound formation and stren gth in Fe alloys have been examined by the calculation of energy and M ulliken's population of cluster models by the extended Huckel method. The results of the present work are as follows: 1) The stability of al loy systems and the nature of chemical bonds between Fe atoms and allo ying atoms can be estimated based on the cohesive energy, atomic bond populations and atomic populations. 2) The tendency of mutual solid so lubility, insolubility and compound formation in Fe alloys can be judg ed as follows: a) In the case of elements which make compounds and hav e no mutual solubility with Fe, the change of cohesive energy with the composition deviates markedly from lineality and the nature of chemic al bonds is ionic or covalent. b) In the case of elements which make c ompounds and have mutual solubility with Fe, the change of cohesive en ergy with the composition deviates a little from lineality and the nat ure of bonds is the mixture of (an ionic or covalent bond) and a metal lic bond. c) In the case of elements which make no compounds and have mutual solubility with Fe, the cohesive energy changes linearly with t he composition and the nature of bonds is a metallic bond or its mixtu re with a covalent or ionic bond. d) In the case of elements which mak e no compounds and have no mutual solubility with Fe, the change of co hesive energy with the composition deviates a little from lineality an d the nature of bonds is anti-bonding. 3) The hardening ability of sol ute atoms in Fe alloys may be attributed to the (covalent + ionic) par t in the nature of chemical bonds between Fe atoms and solute atoms.