Crystallization of amorphous Zr2Pd and Zr3Rh alloys

Abstract

The thermal stability behavior of the metallic glasses a‐Zr₂Pd and a‐Zr₃Rh was studied by means of x‐ray diffraction, differential scanning calorimetry (DSC), and isothermal annealing. While several a‐Zr₂Pd alloys each exhibit two exothermic peaks during the DSC heating sequence, three different types of exothermic behavior have been observed for a‐Zr₃Rh alloys with nominally identical stoichiometries. These variations in DSC behavior are probably related to different conditions during the rapid quenching procedures. The three types of differential scanning calorimeter behavior shown by a‐Zr₃Rh alloys include (1) two peaks of about 715 K and 790 K, (2) a single large peak at about 730 K, and (3) a strong peak at about 725 K with a much weaker peak at about 850 K. The a‐Zr₃Rh alloys of type (1) crystallize to form a tetragonal lattice that is a newly identified Zr₃Rh phase of the D0_e structure type. The a‐Zr₃Rh alloys of types (2) and (3) crystallize first to form a face‐centered cubic lattice which appears to be an E9₃‐type structure. Both the D0_e and E9₃ phases are metastable and ultimately anneal to the Zr₂Rh phase with the tetragonal C16‐type structure. The formation of the Zr₂Rh phases with either the C16 or E9₃ structure is accompanied by α‐Zr. The a‐Zr₂Pd alloys undergo a two‐step crystallization with the initial formation of a disordered body‐centered‐cubic phase followed by the tetragonal Zr₂Pd phase with the C11b‐type structure.