Grain Boundary Segregation of Carbon and Formation of Nanocrystalline Iron-Carbon Alloys by Ball Milling
Based on a novel defactants (defect acting agents) concept (R. Kirchheim, Acta Materialia 55 (2007) 5129 and 5139), a novel method of understanding and synthesizing NC material was proposed by introducing defactants (segregating solute atoms) into the materials to ease the formation of grain boundaries (GBs) and enhance the formation ability of nanocrystalline (NC) structures. The iron-carbon system was chosen as a model system where carbon acts as the so-called defactant. Iron powders mixed with different amount of graphite were ball milled to prepare NC iron-carbon alloys with different carbon concentrations (Co)-After ball milling, the as-milled powder with relatively low carbon concentration was annealed at a certain temperature to achieve saturation of GBs by carbon atoms. The microstructures of the powders were investigated by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The mean grain sizes (D) of the powders were determined by analyzing TEM dark field images and Xray line profiles. The results indicated that once the saturation of GBs is achieved, D of the NC ironcarbon powders will be strongly dependent on Co and will follow a simple mass balance of carbon in a closed system, i.e. D=3gbVm/(Co-Cg) with Cgthe carbon concentration in grains, Fgb the grain boundary excess, and Vm the molar volume of iron. Based on the experimental results, the formation of NC iron-carbon alloys was treated in detail within the framework of the defactant concept. The increase of Q significantly reduces the formation energy of GBs, leading to a substantial decrease of D.
Yuzeng Chen Andreas Herz Reiner Kirchheim
Institut fur Materialphysik,Georg-August-Universitat Gottingen,Friedrich-Hund-Platz 1,D-37077 Gottingen,Germany
国际会议
5th International Conference on Nanomaterials by Severe Plastic Deformation(第五届剧烈塑性变形纳米材料国际会议)
南京
英文
265-270
2011-03-01（万方平台首次上网日期，不代表论文的发表时间）