BCC alloys have unique properties as structural or functional materials; at present they are mainly produced by the ingenious technological processes. Of particular interest are the promising functional materials based on BCC alloys containing nanoscale elements in the structure. It is important to emphasize that the pre-transitional low-stability state of a system is understood to mean its state near the structural-phase transformation in which anomalies of structure or properties are observed. It is this state that provides the functional properties of ‘smart’ materials, allowing one to vary the physicomechanical properties by changing external conditions. The analysis of the effect of the concentration of vacancies on the structural phase states and energy characteristics during heating and cooling showed that the presence and concentration of vacancies turn out to be significant factors in the region of pre-transitional low-stability structural phase states before the transformation.