Ferromagnetic bulk amorphous alloys
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I.
HISTORY OF THE DEVELOPMENT OF BULK AMORPHOUS ALLOYS
SINCE the first synthesis of an amorphous phase in an Au-Si system by rapid solidification in 1960,[1] there has been a strong demand for obtaining a bulk amorphous alloy at a lower cooling rate. For the subsequent 3 decades before 1990, a great number of amorphous alloys have been synthesized with the aim of obtaining an amorphous alloy exhibiting useful properties and a large glass-forming ability. When attention is paid to bulk amorphous alloys with low critical cooling rates for glass formation, it is known that Pd40Ni40P20[2] and Pd76Cu6Si18[3] amorphous alloys can be produced in a bulk form with diameters up to 3 and 0.3 mm, respectively, by water quenching. Subsequently, a flux treatment using a B2O3 medium for the Pd-Ni-P alloy was noticed to be effective in increasing the maximum sample thickness for glass formation, and the maximum thickness has been reported to reach about 10 mm.[4,5,6] Thus, for the long period before 1990, no other bulk amorphous alloys except the Pd- and Pt-based systems have been synthesized, because of the necessity of high cooling rates above 105 K/s for glass formation. Recently, a number of bulk amorAKIHISA INOUE, Professor, and AKIRA TAKEUCHI and TAO ZHANG, Research Associates, are with the Institute for Materials Research, Tohoku University, Sendai 980-77, Japan. This article is based on a presentation made in the ‘‘Structure and Properties of Bulk Amorphous Alloys’’ Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10-11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory. METALLURGICAL AND MATERIALS TRANSACTIONS A
phous alloys with critical cooling rates below 103 K/s have been found in multicomponent alloy systems of Ln-AlTM,[7,8] Mg-Ln-TM,[9,10] Zr-Al-TM,[11,12] Zr-Ti-Al-TM,[13,14] Ti-Zr-TM,[15] Zr-Ti-TM-Be,[16] and Pd-Cu-Ni-P[17] (Ln 5 lanthanide metal and TM 5 transition metal). Table I summarizes the alloy systems of the bulk amorphous alloys, the years when their alloy systems were found, and the maximum sample thickness and critical cooling rate for glass formation. It is to be noticed that the maximum sample thickness reaches about 30 mm for the Zr-Al-TM[18] and Zr-Ti-Al-TM-Pd[19] alloys, 25 mm[20] for the Zr-Ti-TM-Be alloys, and 40[17] to 72 mm[21] for the Pd-Cu-Ni-P alloy. However, these bulk amorphous alloys found before 1993 had been limited to nonferrous metal–based systems, and no bulk amorphous alloys with ferromagnetism at room temperature had been obtained. If we succeed in finding a ferromagnetic bulk amorphous alloy, it is expected that the finding will cause a significant increase in the engineering importance of bulk amorphous alloys. Based on the previously described new multicomponent systems, we have proposed[22–28] the three empirical rules
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