Microstructural Evolution of a Nickel Ferrite–Copper Alloy Cermet During Sintering and High‐Temperature Oxidation
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%
/20% Cu and a ceramic of composition
90% Ni 2 NiFe 4/10% O 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 NiO to CuO 2 Cu 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.
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Document Type: Research Article
Publication date: October 1, 2012