Effect of milling temperature and additive elements on an Fe-C system alloy prepared by mechanical alloying

摘要

Mechanical alloying (MA) of elemental powder mixtures of Fe-C and Fe-C-X (X = Si and Cr) was performed in an argon atmosphere at various temperatures using a planetary ball mill. MAed powders were examined by X-ray diffractometry, differentialthermal analysis and scanning electron microscopy. MAed powders were hot isostatic pressed (HIPed) at both lower and higher temperatures than that of the eutectoid transformation point A{sub}1. The Vickers hardness and microstructure of HIPed compactswere examined. In the first stage of milling, amorphization of graphite occurs. As the milling time increases, super-saturated iron solid solution is formed by repeating fracture and cold-welding of iron powders. The iron/carbon amorphization and thesolution of carbon atom into iron solid solution progress parallel with each other. Finally the iron/carbon amorphous is formed entirely. This behavior depends on the milling temperature. The Vickers hardness of the HIPed compact is maximal at a carbonconcentration of 6 mass% for HIP at 853 K and 7 mass% for HIP at 1053 K, respectively. The hardness depends on the density of voids and the amount of Fe{sub}3C and graphite. Graphitization of Fe{sub}3C is promoted by silicon addition but retarded bychromium addition.