Corrosion behavior of amorphous fe-cr-al-p-c ribbon alloys
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I.
INTRODUCTION
L O T S of efforts have been made to develop the fundamental and application studies on amorphous alloys since the rapid quenching method from the liquid ~ was found. Much attention has been directed to these materials from those engaged in the studies not only of physics and metallurgy but of chemistry. 2'3 It has been reported by Hashimoto and his co-workers 4-s that many kinds of amorphous alloys revealed an extremely high corrosion resistance in acidic and neutral solutions. From the corrosion studies, they considered that the high corrosion resistance of amorphous alloys should be attributed to the chemical homogeneity and the immediate formation of passive thin film. It was investigated by Naka, Hashimoto, and Masumoto 4 that the amorphous Fe72CrsPj3C7 alloy has the high corrosion resistance in various corrosion solutions. In this amorphous system, the composition of Cr functions mainly to form the passive thin film on condition that the inclusion of Cr element is more than eight at. pct in the composition. With an aim to decrease Cr content of this alloy, A1 was introduced into the system in our present work. The amorphous Fe72Crs_xAlxPt3C7 systems revealed the high corrosion resistance with the almost same degree as the amorphous Fe72CrzPI3CT. In particular, even in the system with the low content of Cr, the amorphous alloys showed the high corrosion resistance inthe solutions employed here.
II.
EXPERIMENTAL
All the master ingots were prepared by melting commercial metals and metalloids in an induction furnace with an argon atmosphere. Amorphous alloy ribbons of 2 to 3 mm in width and 20 to 50 /zm in thickness were prepared by means of the rotating wheel method. 9 A jet of molten alloys is to impinge on the stainless steel surface of a rapidly rotating wheel through a quartz nozzle. This wheel is of 200 mm in diameter and 40 mm in thickness, and its rotating speed can be controlled at 2800, 4600, and 5800 rpm. The corrosion solutions used here were as follows: 1N-HC1, IN-H2SO4, 1N-NaOH, 3 pet NaCI, and 10 pct FEE13 9 6H20, which were prepared with the reagent grade chemicals and deionized water. An immersion test of amorphous ribbons was carried out in the solutions at the temperature of 303 - 1 K. Before and after immersion of the KANGJO CHO, Professor, CHOLL-HONG HWANG, Associate Professor, YEONG-JO RYEOM, Research Assistant, and CHANG-SU PAK, Laboratory Asststant, are all with the Department of Metallurgy, Faculty of Engineering, Korea University, Ogawa, Kodaira, Tokyo 187, Japan. Manuscript submitted August 26, 1981. METALLURGICALTRANSACTIONS A
sample into solutions, the sample weight was measured to obtain the weight discrepancy. Prior to electrochemical measurements, the specimens were put in a cycrohexan solution and then were polished mechanically with silicon carbide paper up to No. 1000. Electrolytes were exposed to air. Anodic polarization curves of amorphous Fe-A1-P-C and Fe-Cr-AI-P-C alloys were measured potentiodynamically at a potential sweep rate of 4 • 102 sec-V -l in
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