Synthesis and Properties of Bulk Metallic Glasses in Pd-Ni-P and Pd-Cu-P Alloys
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Tm, to the glass transition
temperature, Tg. Recently, a number of multicomponent metallic alloy systems have been found to have extraordinary glass forming ability. These alloy systems include La-Al-(Ni,Cu) [1], Mg(Cu,Ni)-Y [2], Zr-AI-(Cu,Ni,Co) [3,4], Zr-Ti-Cu-Ni-Be [5], Nd-AI-(CuNi,Co,Fe) [6], and Ti-ZrNi-Cu [7]. Most of these alloys can be quenched from the melt into a bulk amorphous state at a relative cooling rate of 1-100 K/sec. By bulk we mean a sample with minimum dimensions of about 1 mm. Because bulk amorphous alloys have large technological potential, understanding their synthesis and finding new compositions are topics of great scientific interest. Pd 40 Ni 40P20 was one of the first bulk amorphous alloys discovered. By quenching the melt in water, Chen produced amorphous Pd40 Ni40 P20 alloy rods with diameters of 1-3 mm [8]. Using surface etching and thermal cycling to eliminate the surface impurities, Drehman et al. [9] successfully produced amorphous Pd 40 Ni40 P20 solids with minor diameters up to 5.3 mm; and by fluxing molten Pd40 Ni4 0P20 with dehydrated B2 0 3 , Kui et al. [10] were able to prepare amorphous Pd 40 Ni40 P20 buttons with the minimum dimension of about 10 mm. These previous studies have concentrated on the particular composition of Pd 40 Ni4 0P20. In recent publications, we reported the homogeneity range for bulk glass formation in the Pd-Ni-P system [11,12]. In this paper we report a new ternary bulk glass forming system, Pd-Cu-P. The properties of bulk Pd-Cu-P and Pd-Ni-P glasses are compared and discussed.
495 Mat. Res. Soc. Symp. Proc. Vol. 455 ©1997 Materials Research Society
SYNTHESIS OF BULK AMORPHOUS ALLOYS The synthesis of bulk amorphous Pd-Ni-P and Pd-Cu-P alloys was based on an improved fluxing technique [11,12], which was pioneered by Tumbull and his colleagues [9,10]. The alloy synthesis starts by mechanically allying mixtures of elemental powders [13]. The alloyed powders are then purified in molten B20 3 which dissolves oxide impurities which would otherwise act as heterogeneous nucleation centers in the undercooled molten alloy. The bulk amorphous alloy was formed by quenching the molten alloy in water. The cooling rates are estimated at no more than 100 K/s. The structure and properties of the amorphous alloys was investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, scanning differential calorimetry (DSC), and resonant ultrasound spectroscopy (RUS). BULK GLASS FORMATION RANGE Pd-Ni-P System Using the fluxing technique, bulk amorphous Pd-Ni-P alloy rods with a critical diameter of 10 mm can be formed over a wide range of metal compositions, as indicated in Fig. 1. For bulk glass formation, however, the phosphorus concentration must be maintained close to 20 at.%. Previous research has shown that the glass forming ability correlates with the difference AT = Tx - Tg. For the Pd-Ni-P system, AT is largest for Pd 40Ni 40 P20 and we have found that amorphous Pd40Ni40 P20 cylinders, 25 mm in diameter and 300 g in weight, can be easily p
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