INVERSE MELTING OF A METASTABLE NB45CR55 SOLID-SOLUTION

An Nb45Cr55 solid solution was prepared by mechanical alloying in a planetary ball mill and investigated by x-ray diffraction and calorimetry. It was found that the structure evolution upon heating exhibited three distinct stages, the first resulting in complete amorphization, whereas the second and third are related to the subsequent crystallization of the amorphous phase. These results are in agreement with the free-energy functions calculated from the thermochemical data of the system. They show that for a composition of Nb45Cr55 a second melting point (often termed ''inverse melting point'') exists at about 900-degrees-C, below which the undercooled liquid has a lower free energy than the crystalline body-centered-cubic phase.