INVERSE MELTING OF A METASTABLE NB45CR55 SOLID-SOLUTION

An Nb45Cr55 solid solution was prepared by mechanical alloying in a pl anetary ball mill and investigated by x-ray diffraction and calorimetr y. It was found that the structure evolution upon heating exhibited th ree distinct stages, the first resulting in complete amorphization, wh ereas the second and third are related to the subsequent crystallizati on of the amorphous phase. These results are in agreement with the fre e-energy functions calculated from the thermochemical data of the syst em. They show that for a composition of Nb45Cr55 a second melting poin t (often termed ''inverse melting point'') exists at about 900-degrees -C, below which the undercooled liquid has a lower free energy than th e crystalline body-centered-cubic phase.