On the nature of the electrochemically synthesized hard Fe-0.96 mass pct C alloy film
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I. INTRODUCTION
THE most important of all structural materials, steels, are basically alloys of iron and carbon. The ability of FeC–based alloys to transform into a martensitic structure of high hardness upon proper heat treatment is one of the main reasons for their widespread use in machine components. In industrial practice, a hard martensitic structure is achieved by heating steels to a temperature around 1123 K or higher, followed by rapid quenching. Thus, achieving hard Fe-C– based alloys through low-temperature processing routes can be rather attractive from practical as well as theoretical points of view. It was reported that hard Fe-C alloys with 0.43–1.26 mass pct C can be obtained directly by electrochemical deposition or electrodeposition at 323 K from sulfate-based baths containing a small amount of citric acid and L-ascorbic acid.[1,2,3] Izaki et al.[3] found that the hardness of the electrochemically deposited Fe-C alloy with 1 mass pct C was around 812 HV, a value close to that of the thermally prepared Fe-C martensite. A similar hardness in electrochemically deposited Fe-C alloys was also found in other studies.[4,5] The effects of electrodeposition parameters on the carbon content of the alloys were also described in these latter studies. These electrochemically synthesized hard FeC alloys have the potential to replace hard chrome plating and carburizing, in some cases. The use of electrodeposited Fe-C alloys, instead of the electrodeposited iron currently in use, in the salvage of worn components can extend their service life. This process can also lend itself to direct electroforming of small complex-shaped components. The possibility of incorporation of alloying elements like nickel also exists. Although the electrochemically deposited Fe-C alloys are A.S.M.A. HASEEB, Professor, is with the Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka 1000, Bangladesh. Contact e-mail: haseeb@ mme.buet.ac.bd or [email protected] Y. HAYASHI, Professor, M. MASUDA, Associate Professor, and M. ARITA, Research Associate, are with the Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, 6-10-1 Hakozaki, Fokuoka 812-8581, Japan. Manuscript submitted February 4, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
loosely termed as martensitic, presumably because of their high hardness,[1–5] their exact nature is yet to be understood. It has been revealed by X-ray diffraction (XRD) study[1] that in spite of its high hardness, the tetragonality of the electrodeposited Fe-1.21 mass pct C alloy is very small. The c/a ratio of the electrodeposited alloys was found to be 1.005, as compared to 1.059 for the thermally prepared martensite of similar composition. Moreover, the characteristic laths in the microstructure of quenched Fe-C martensite were not observed in the electrochemically deposited FeC alloys.[3] This work presents some structural, thermalstability, and magnetization data on an electrodeposited FeC al
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