Effect of Ga addition on the glass-forming ability of Fe-based bulk glassy alloy

Abstract

It has been clarified that Fe Al Ga P C B bulk glassy alloy exhibits high glass-forming ability and good soft magnetic properties [1–3]. Recently, we have developed a number of Fe-based bulk glassy alloys with high glass-forming ability in Fe (Cr, Mo) Ga P C B and Fe Co Ga P C B systems [4–6]. Furthermore, with the aim of increasing saturation magnetization (Is), we also developed Fe Ga P C B and Fe Ga P C B Si bulk glassy alloys in which the content of Fe is higher than the above-described alloys [7–9]. These bulk glassy alloys with diameters of 1 to 2.5 mm can be easily prepared by copper mold casting and exhibit high Is of 1.3 to 1.4 T. Here, it is noticed that Ga is a common element in all these alloys. This paper intends to investigate the reason why the addition of Ga to Fe P C B alloys is effective in enhancing glass-forming ability. Multi-component Fe80P13C7, (Fe0.8P0.13C0.07)95Ga5, [(Fe0.8P0.13C0.07)0.95Ga0.05]95B5 and Fe80−x Gax P12C4B4 alloys were examined in the present study. The ingots were prepared by induction melting a mixture of pure Fe and Ga metals, prealloyed Fe-C and Fe-P ingots, and pure B crystal in a purfied argon atmosphere, respectively. Their compositions are nominally expressed in atomic percentage. From the master alloy ingot, a ribbon with a cross section of about 0.020 × 1.0 mm2 was prepared by melt spinning. The amorphicity of the ribbons was examined by X-ray diffractometry with Cu-Kα. The specific heat associated with glass transition, supercooled liquid region and crystallization was measured at a heating rate of 0.67 K/s with a differential scanning calorimeter (DSC). The liquidus temperature (T1) of alloys was measured by cooling the molten alloy samples at a rate of 0.033 K/s with a differential thermal analyzer (DTA). It was confirmed by X-ray diffraction that the present melt-spun Fe80−x Gax P12C4B4 alloy ribbons were composed of an amorphous phase without any crystallinity over the whole composition range up to 10 at.% Ga. Fig. 1 shows the DSC curves of Fe80−x Gax P12C4B4 (x = 0 to 10 at.%) glassy alloys. All the glassy alloys exhibit a glass transition and a supercooled liquid region prior to crystallization. The supercooled liquid region, defined as the difference between the glass transition temperature (Tg) and the onset temperature of crystallization (Tx), Tx (=Tx − Tg), increases into the range of 25 to 37 K with increasing Ga content from 1 to 5 at.%, accompanying an increase in Tg and Tx. A distinct supercooled liquid state with full structural relaxation is observed for the 5 at.% Ga alloy. It is clearly seen that the supercooled liquid region in an internal equilibrium state is retained over a temperature interval of 20 K. The further increase in Ga content to 10 at.% causes a decrease in Tx and the largest Tx of 37 K is obtained for the 5 at.% Ga alloy. Fig. 2 shows the DSC curves of the Fe80P13C7, (Fe0.8P0.13C0.07)95Ga5 and [(Fe0.8P0.13C0.07)0.95Ga0.05]95B5 glassy alloys. The Fe80P13C7 alloy is a typical amorphous ferromagenetic alloy with good soft magnetic properties developed in 1974 [10]. As shown in the figure, there is no distinct supercooled liquid state with full structural relaxation for Fe80P13C7