Abstract
We present a simple band model for the computation of the density of states and the enthalpy of formation for transitional alloys in the sigma phase. We apply this model for the computation of phase diagrams of ternary alloys between elements of the first transition row and we show that the good agreement obtained with experiment arises from the particular shape of the enthalpy of formation in the sigma phase, which deviates considerably from the parabolic law obtained in the regular solution approximation.