The structural relaxation occurring in a Pd40Cu 30Ni10P20 metallic glass on annealing at temperatures that are both above and below its glass transition temperature (Tg) is investigated using differential scanning calorimetry (DSC). Bulk (slowly cooled) as well as ribbon (rapidly quenched) forms of the alloy were examined, in order to assess the connection between the cooling rate and subsequent relaxation behavior. An 'excess' enthalpy peak at Tg in the DSC scans, which appears irrespective of the annealing temperature (T a), is considered as a characteristic signature of relaxation. At a given Ta, the recovery increases rapidly with the annealing time (ta) before saturating. The rate of increase of the recovery is higher in the ribbon, but with a lower saturation value vis-à-vis that in the bulk, implying that the latter is more resistant to relaxation at low Ta. This is probably due to entirely different relaxation mechanisms in these two materials; free-volume annihilation in the ribbon and short-range ordering in the bulk. The enthalpy peak is a manifestation of the destruction of the short-range order that is induced on annealing. The short-range order may be compositionally different from crystallization nuclei, leading to improvement of the thermal stability of the glass. The activation energy calculations, reveal that the annealed ribbons transcend the glass transition more easily than the melt-spun ribbon, while the annealed bulk samples undergo the transition with more difficulty than the as-cast bulk sample. Furthermore, the ribbon is more susceptible to crystallization as compared to the bulk on annealing at the same temperatures.
|Number of pages||8|
|Journal||Transactions of the Indian Institute of Metals|
|Publication status||Published - 2006 Apr 1|
ASJC Scopus subject areas
- Metals and Alloys