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Microstructural Evolution of a Nickel Ferrite–Copper Alloy Cermet During Sintering and High‐Temperature Oxidation
Author(s) -
Tao Yuqiang,
Li Zhiyou,
Zhang Dou,
Xiong Huiwen,
Zhou Kechao
Publication year - 2012
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.1551-2916.2012.05305.x
Subject(s) - cermet , materials science , sintering , alloy , microstructure , oxide , metallurgy , non blocking i/o , porosity , ferrite (magnet) , copper , internal oxidation , nickel , ceramic , composite material , chemistry , catalysis , biochemistry
The microstructural evolution during sintering and high‐temperature oxidation of a cermet comprised of (wt%) a 40/60 ratio of an alloy of composition 80% Cu /20% Ni and a ceramic of composition 90% NiFe 2 O 4 /10% NiO has been studied as a function of processing temperature. The porosity of the cermet reduced significantly without undue coarsening of the microstructure during sintering up to the melting temperature of the alloy phase ( T m ≈ 1160°C), whereas at sintering temperatures higher than T m , the ferrite rapidly coarsened with little additional reduction in porosity, and the alloy phase formed a continuous interconnected network while partially extruding from the composite. Upon oxidation in air at temperatures between 850°C and 1000°C, the cermet developed a multilayered oxidized scale, comprising a thin copper‐rich outer oxide layer formed via external oxidation and a thicker zone of internal oxidation. The external oxide scale transformed from CuO to Cu 2 O with increasing oxidation temperature. Out‐diffusion of the copper to the externally oxidized layer led to significant porosity at the internal interface between oxide and unoxidized cermet.