Influence of Ga Substitution on the Nature of Glasses in Zr_(69.5)Al_(7.5-x)Ga_xCu_(12)Ni_(11) and Ce_(75)Al_(25-x)Ga_x Metallic Glass Compositions

摘要

In this presentation, results of our recent investigations on the role of Ga on Al site in Zr_(69.5)Al_(7.5-x)Ga_xCu_(12)Ni_(11) and Ce_(75)Al_(25-x)Ga_x metallic glass compositions will be discussed. Ga like Al is normally expected to be in trivalent state. However, it may go in monovalent state depending on other alloying elements. The rapidly solidified melt spun ribbons of above two alloys gave rise to two important conclusions. The Zr_(69.5)Al_(7.5-x)Ga_xCu_(12)Ni_(11) system displayed metallic glass formation in the range of x=0 to 7.5. In this process, we have come out with a new composition of glass without Al corresponding to x=7.5. In contrast to the above, for Ce-Al(Ga) system, we have observed phase separation in glass after dilute substitution of Ga. It seems that such a phase separation in this system cannot be understood in terms of summation of enthalpy of mixing of the various possible binaries in this system. The substitution of Ga in different valence states might have created chemical pressure leading to creation of two types of distinct major clusters. The phase separation may be due to this. This has also given rise to excursion of Ce 4f-states of the alloy. This and aforesaid 'chemical pressure' will be corroborated based on results of binary Ce-Al system under pressure by other investigators.