Glass-Forming Ability and Crystallization of High Purity Pd-Cu-Ni-P Alloy
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Glass-Forming Ability and Crystallization of High Purity Pd-Cu-Ni-P Alloy Nobuyuki Nishiyama, Mitsuhide Matsushita and Akihisa Inoue1 Inoue Superliquid Glass Project, ERATO, JST, Sendai 982-0807, JAPAN 1 Institute for Materials Research, Tohoku University, Sendai 980-8577, JAPAN ABSTRACT Glass-forming ability, thermal stability and nucleation behavior of a Pd40Cu30Ni10P20 alloy prepared using a high purity polycrystalline phosphorus are investigated. The critical cooling rate for glass formation for the high purity alloy is the same as that for the previous result, but the improvement of undercooling reaches about 80 K as compared with the fluxed ordinary alloy. In comparison with the non-fluxed alloy, the solidified structure of the present highly purified alloy is significantly different. The non-fluxed sample shows the characteristic “island-like” structure consisted of acicular fcc-Pd2Ni2P solid solution and Cu3Pd intermetallic compound. These acicular phases appear to be caused by the growth of quenched-in nuclei. In the isothermal experiment, nucleus density exhibits time dependence even at 683 K near the nose temperature. It is assumed that the crystallization behavior for the highly purified alloy is closer to homogeneous nucleation from quenched-in nuclei dominant behavior. In order to investigate the nucleation behavior, in-situ TEM observation was carried out. Spherical Pd15P2 particle with a diameter about 15 nm is observed, and this spherical region repeats generation and annihilation during isothermal annealing. The reason for the high glass-forming ability is discussed on the basis of the obtained results. INTRODUCTION In the last decade, a number of multi-components alloys with particular alloy combinations such as Ln- [1,2], Mg- [3,4], Zr- [5-7], Fe- [8,9] and Co- [10] systems have been reported to have a high glass-forming ability (GFA) which leads to the formation of bulk metallic glasses (BMG). In particular, a new quaternary Pd-Cu-Ni-P metallic glass [11] has an outstanding high GFA, and much effort has been devoted to prove its exceptional high resistance against crystallization in an undercooled liquid state [12-14]. The exceptional high GFA and high thermal stability gave us a unique opportunity to access a number of physical properties for the undercooled alloy. For example, the critical cooling rate ( Rc ) of 0.1 K/s for glass formation [13], viscous flow behavior [15], dynamic viscoelastisity [16], local atomic structure [17,18], crystallization kinetics [19,20], electrical resistivity [21,22], atomic diffusion [23], thermal expansion and specific volume [24] thermodynamic property [25] and elastic property by ultrasonic measurement [26] have been reported. However, the direct reason for the achievement of high GFA remains unknown. If the thermal stability against crystallization could be enhanced, it is possible to obtain useful knowledge for further deep understanding of GFA. Nishiyama et al. have already pointed out that the crystallization behavior of the undercooled melt is dominated
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