Abstract
A
polycrystalline Cantor alloy, equimolar in Co, Cr, Fe, Mn and Ni, was cast. It
was subjected to oxidation in a thermo-balance in a flow of synthetic dry air,
at 1000, 1050, 1100 and 1150 °C. The mass gain was globally parabolic but rather
irregular. The parabolic constants, ranging from 55 to 700 × 10
−12·g
2·cm
−4·s
−1,
are much higher than for a chromia-forming alloy. They obey an Arrhenius law
with an activation energy equal to 270 kJ/mol. The external oxide scales formed
are composed of an outer part made of manganese oxide and an inner part made of
(Cr, Mn) oxide containing a thin internal layer of chromia. The Mn and
Cr-depleted depths and the Mn and Cr masses lost by the alloy increase with the
oxidation temperature. Cr-rich acicular particles precipitated in subsurface at
1100 °C
and internal oxidation along the grain boundaries are present in the whole
thickness of the sample oxidized at 1150 °C. Oxide spallation occurred during
the cooling, at temperatures in the 200–350 °C range, only for the alloys
oxidized at 1050 and 1100 °C. Not too thick scale (1000 °C) or deep internal oxidation
(1150 °C)
may be favorable for scale adherence.
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