Phase transformation behaviour in continuously cooled Zr₆₅Al_7.5Ni₁₀Cu_17.5−xPd_x (x= 0 − 17.5) glass-forming alloys and consequences for structure and property control

Abstract

Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr₆₅Al_7.5Ni₁₀Cu_{17.5− x} Pd _x (x = 0 − 17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x = 5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x = 17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x = 5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x = 17.5).

Keywords:

• metallic glasses
• phase transformation
• undercooling
• quasicrystals

Acknowledgements

This work was supported by a Grant-in-Aid for Priority Areas on ‘Materials Science of Bulk Metallic Glasses’ and ‘Scientific Research B’ from the Ministry of Education, Sports, Culture, Science and Technology, Japan and Japan Science Promotion Society (JSPS), Asian Core Program.