電析Fe-C合金膜の相変態と硬度変化

概要

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Iron-carbon alloy films with 0.43 to 1.18mass%C were electrodeposited from an iron (II) sulfate solution containing small amounts of citric acid and L-ascorbic acid. Phase transformations and hardness changes in the alloy films resulting from annealing at 473K to 1173K for 3.6ks were studied by X-ray diffraction and hardness measurement. The alloy films had a single martensitic phase with a body-centered tetragonal structure, and the axial ratio of the phase increased with the increase in the C content in the films. A new intermediate carbide phase and Fe3C phase were formed on annealing at 623K and 1173K. The intermediate carbide phase had an orthorhombic structure with a=0.4787nm, b=0.4360nm and c=0.2902nm. The increase in the hardness of the Fe-C alloy films at carbon contents of above 1mass% started at around 473K, and softening began at about 753K. The alloy films annealed at temperatures between 473K and 753K showed the hardness of Hv 1000 to Hv 1100 at room temperature.