Direct evidence of free-volume relaxation and the crossover effect in Ni25Zr55Al20 metallic glass

✍ Scribed by K. Krištiaková; J. Krištiak; P. Švec; O. Šauša; P. Duhaj

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 629 KB
• Volume: 39
• Category: Article
• ISSN: 0921-5107
• DOI: 10.1016/0921-5107(95)01529-9

✦ Synopsis

The changes in positron annihilation lifetime in a thermally treated Ni,,Zr,,Al,, alloy were observed. The glass transition temperature T, lies around 700 K. Isothermal annealing was used to treat samples sequentially in the amorphous (at 640 K) and the undercooled liquid (at 740 K) states. This provides insight into the microstructural processes taking place via determination of the evolution of the positron capture site density and distribution. The observed shifts in the positron lifetime distribution are analyzed in terms of relaxation of the free volume V, i.e. chemical and topological short-range ordering (CSRO, TSRO) which are known to be influenced in an important manner by the relaxation processes. The upper limits of the activation energies of the two relaxation processes (2.2 and 2.6 eV) are determined. For the first time, the "crossover" effect in the free-volume distribution has been observed.