EFFECT OF BORON OR CARBON ON AMORPHOUS FORMATION OF LA55AL25NI20 ALLOY

The area ratio of the amorphous region formed by water quenching is qu antitatively observed when boron or carbon is added to a La55Al25Ni20 alloy. The pre-formed specimen, which is the size of 12 mm in diameter and 6 mm in thickness, is made by a high frequency induction heating. The disk specimen is made by quenching the pre-formed specimen into w ater after heating it in an Ar how. The area ratio of the amorphous re gion is measured by image processing of the image given by an optical microscope. The ratio depends on the temperature before quenching of t he alloy and on the added amounts of boron or carbon. In the case of B addition, the area ratio of the amorphous region sensitively depends on the quenched temperature and the amount of the addition. In the cas e of C addition, the ratio becomes almost 100% at the quenching temper ature from 953 to 1113 K with the addition from 1.5 to 5 at%. Taking a ccount of the measured ratio of the amorphous phase to the super-coole d region of the liquid measured with DSC, we conclude that an amorphou s formability of La55Al25Ni20 can be improved highly by about 5 at%C a dded in the size of our specimen.