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 FexCu100 − x (x=0x=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.