Positive excess volume of liquid Fe-Cu alloys resulting from liquid structure change

The densities of liquid Fe-Cu alloy system were investigated in the temperature range of 1200-2000 K, covering both a superheating range and a large metastable undercooled regime. For all the Fe_xCu_{100 - x} (x=0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100) alloys, the density is a linear function of temperature. In all the cases, the densities of Fe-Cu alloys with different compositions are smaller than those of ideal solution. This indicates that Fe-Cu alloys deviate from ideal solution and have positive excess volumes. Furthermore, the liquid structure change is described by the pair distribution function and the coordinate number for different liquid Fe-Cu alloys. It is revealed that the atomic packing degree is responsible for the positive excess volume. Moreover, the thermal expansion coefficients are also derived and display a rise with the increase of Cu content.