Magnetic Behavior and Structure of Electrodeposited, Mechanically Hard Fe-C and Fe-Ni-C Alloys
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Magnetic Behavior and Structure of Electrodeposited, Mechanically Hard Fe-C and Fe-Ni-C Alloys A. S. M. A. Haseeb*, Y. Hayashi and M. Masuda Department of Materials Science and Engineering, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan *Permanent address: Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka 1000, Bangladesh. ABSTRACT Iron-carbon based hard, martensitic alloys are usually produced by conventional high temperature heat treatment. In the present work, the galvanostatic electrodeposition method has been employed to obtain hard Fe-0.96 mass % C and Fe-15.4 mass% Ni-0.70 mass% C alloys at around room temperature. The alloys have been investigated by SEM, XPS, XRD, and microhardness measurements, and their magnetic properties have been studied by vibrating sample magnetometer. The as-deposited alloys were found to possess high mechanical hardness, 750-810 HV. Both alloys exhibit a smoother surface morphology as compared to a non-alloyed iron film obtained under similar electrochemical conditions. The coercive force of the as-deposited Fe-C and Fe-Ni-C alloys is 3930 and 494 A.m-1 respectively. In comparison, pure iron film deposited under similar conditions possesses a coercive force of 1592 A.m-1. The Fe-Ni-C alloy has a combination of high mechanical hardness and relatively soft magnetic properties, which may be of interest in potential applications requiring both soft magnetic properties and improved tribological performance. The effects of annealing on the behavior of the alloys are discussed. INTRODUCTION Electrodeposition is often known to provide microstructures that are difficult and sometimes not quite attainable through conventional processing routes. Recently, it has been demonstrated [1-3] that iron-carbon alloy films with hardnesses as high as those of thermally quenched Fe-C martensite can be produced by electrodeposition. This is rather interesting because while hard Fe-C martensite is conventionally prepared by high temperature heat treatment (involving heating to 850 °C or higher, followed by rapid quenching), electrodeposition of the hard Fe-C alloys can be done directly near room temperature (50 °C). It was found [1], however, that in spite of the similar hardnesses, the tetragonality of the crystal structure of the electrodeposited alloys was far lower than that of the thermally quenched martensite. This indicates that detailed structure of the electrodeposited Fe-C alloys is different from that of their thermally processed counterparts. Fe-metalloid (C, N, B) systems are not only known for high mechanical hardness, their magnetic properties have also been of interest for some time [4-7]. Recently, there has been a trend toward decreasing the head-media distance in magnetic information storage systems. This implies that the head may actually contact the asperities of the disc during operation [8]. Under these contact situations, the tribological properties of the materials used becomes quite relevant. Ther
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