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Surface Roughening Transition and Coarsening of NbC Grains in Liquid Cobalt‐Rich Matrix
Author(s) -
Cho Young Kyu,
Yoon Duk Yong,
Kim ByoungKee
Publication year - 2004
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2004.00443.x
Subject(s) - nucleation , materials science , classification of discontinuities , grain growth , sintering , matrix (chemical analysis) , cobalt , surface energy , condensed matter physics , transition temperature , surface (topology) , crystallography , grain size , mineralogy , composite material , metallurgy , geometry , chemistry , thermodynamics , superconductivity , physics , mathematical analysis , mathematics
When NbC–30 wt% Co powder compact is sintered at various temperatures where NbC grains (with small amounts of Co) coexist with a liquid Co–NbC matrix, the NbC grains undergo a surface roughening transition with temperature increase and the grain growth changes from abnormal to normal growth. When sintered at 1400°C, the grains are polyhedral with sharp edges (and corners) and grow abnormally because their singular surfaces move by nucleation of surface steps. When sintered at 1600°C, the edges become round, indicating the surface roughening transition. The grains still grow abnormally, but their number density is larger than that at 1400°C because of the smaller surface step free energy. When sintered at 1820°C, the grains are nearly spherical, but the flat‐surface segments still remain. The grain growth at this temperature is nearly normal because of very small surface step free energy. The surface roughening transition is reversed when a specimen initially sintered at 1820°C is heat‐treated again at 1400°C, but some grains show transition shapes with nearly flat edges and slope discontinuities (shocks).