Influence of Ga Substitution on the Nature of Glasses in Zr 69.5 Al 7.5-x Ga x Cu 12 Ni 11 and Ce 75 Al 25-x Ga x Metall
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Influence of Ga Substitution on the Nature of Glasses in Zr69.5Al7.5-xGaxCu12Ni11 and Ce75Al25-xGax Metallic Glass Compositions R.K. Mandal1, R.S. Tiwari2, Devinder Singh3 and Dharmendra Singh2 1
Metallurgical Engineering, IIT (BHU), Varanasi 221005, UP INDIA Department of Physics, BHU, Varanasi 221005, UP INDIA 3 Department of Physics, Panjab University, Chandigarh 160014, Punjab INDIA 2
ABSTRACT In this presentation, results of our recent investigations on the role of Ga on Al site in Zr69.5Al7.5-xGaxCu12Ni11 and Ce75Al25-xGax 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 Zr69.5Al7.5-xGaxCu12Ni11 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. INTRODUCTION Metallic glasses (MGs) and their nano-composites make them quite unique in comparison to conventional crystalline materials [1, 2] owing to their outstanding resilience. The Zr-based MGs have outstanding mechanical properties at room temperature i.e. high yield-strength (~ 2 GPa), micro plasticity up to 1 %, low Young’s modulus and high fracture toughness [1-4]. MGs form shear bands at room temperature due to localized deformation during micro-/nanoindentation [5, 6]. Another important class of MGs belongs to Ce-based compositions. They display unusual behavior due to variable nature of 4f electronic states [7, 8]. Thus, only small amount of energy is required to change the relative occupancy of the electronic levels e.g. when Ce subjected to high pressure or low temperatures, a volume change of approximately 10% results [8]. Therefore, the structural and physical properties of Ce-based MGs may have different characteristics than those of other known metallic glasses [5-8]. Indentation studies are widely applied to measure the mechanical properties and elastic/plastic deformation responses of MGs [9, 10]. Such studies are necessary to understand the nature of deformation mechanism in metallic glasses. Alloying addition is a powerful method for improving the mechanical properties of MGs by modulating the microstructure [9, 11]. I
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