Room-temperature mechanically induced solid-state devitrifications of glassy Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Pd_5 alloy powders

摘要

The high-energy ball milling technique was employed for synthesizing a single phase of glassy Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Pd_5 alloy powder, using a room-temperature mechanical alloying method. Whereas the glass transition temperature of the obtained glassy alloy is 683 K, the crystallization temperature is 783 K. The mechanically alloyed Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Pd_5 glassy powders maintain their unique disordered structure through a large supercooled liquid region (100 K). The possibility of devitrification of the synthetic glassy phase upon increasing the ball milling time was investigated. The results have shown that the glassy powder that is obtained after 173 ks of milling is subjected to numerous lattice imperfections and tends to transform into a metastable big-cube phase after further ball milling (259-432 ks). After 540 ks of milling, a complete glassy-metastable phase transformation is achieved and the end-product of this stage of milling is nanocrystalline big-cube powder that has a lattice constant of 1.2293 nm. As the milling time increases (720 ks), the obtained big-cube phase can no longer withstand the shear and impact stresses that are generated by the milling media and is transformed into a new metastable phase of nanocrystalline fcc- Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Pd_5. The fcc-metastable phase transforms into a mixture of Zr_2Cu and Zr_6NiAl_2 crystalline phases at rather high temperature, as high as 993 K.