Investigation of specific heat and thermal expansion in the glass-transition regime of Pd-based metallic glasses

The alloys Pd-Ni-P and Pd-Ni-Cu-P have an outstanding glass-forming ability and stability against crystallisation in the undercooled liquid state at t emperatures greater than the glass-transition temperatures. Samples of the copper containing alloys can be vitrified readily by cooling the liquid at rates greater than or equal to 0.1 K/s. This rate allows us to investigate the thermodynamic quantities of this alloy system in the liquid as well as in the glassy state during continuous cooling or heating without interferen ce from crystallisation. In the present work, the specific heat and the vol ume expansion coefficient in the glassy and in the undercooled liquid state were determined at temperatures less than and greater than the glass-trans ition temperature by applying differential scanning calorimetry (DSC) and s essile drop (SD) technique, respectively. The glass temperatures of the sam ples resulting from the cooling rate were investigated during re-heating by both the methods. By comparing the results, a correlation between enthalpy and specific volume as a function of temperature could be demonstrated exp erimentally for these metallic alloys. We attribute the characteristic cour se of the enthalpy and the specific volume in the range of the glass-transi tion to structural relaxation processes and to the fraction of free volume in the glass as a function of temperature and time. (C) 2000 Elsevier Scien ce B.V. All rights reserved.