Oxidation kinetics of chromium and morphological phenomena

Abstract

P02 show good sulphidation resistance due to the higher chromia content in the oxide scale. Yttrium-ion implantation of Incoloy 800H has also a beneficial effect on sulphidation, if preoxidation is applied. The reason for this is presumably the segregation of yttrium to grain boundaries of the oxide. Furthermore, the oxidation kinetics of Incoloy 800H are independent of the partial pressure of the oxygen. Mechanical testing of the preformed oxide scale/substrate combinations in air at 600~ by means of constant-extension-rate experiments shows that preoxidation at low partial pressures of oxygen leads to earlier scalecracking.

On ultra‐high temperature oxidation of Cr–Cr3Si alloys: Effect of germanium

“…As Fig. shows, only alloys SG1 and SG2 show the typical wrinkling , which does not appear in alloys S15 and SG12.…”

“…Scale wrinkling is a common feature that occurs in chromia scales and is attributed to the lateral growth of chromia within the scale . This feature is the result of a stress‐releasing process via plastic deformation of the scale at high temperature .…”

Effect of specimen thickness on chromia scaling of Ni25Cr in N2–O2–H2O test gases at 1000°C

“…23,24 In explaining experimental observations, some authors 19,23,24 assumed that classical defect equilibria related to an oxide lattice are applicable for describing transport processes along grain boundaries. Although it has not yet unequivocally been demonstrated that this is indeed the case, this assumption is also followed in the present considerations.…”

Effect ofin-situgas changes on thermally grown chromia scales formed on Ni–25Cr alloy at 1000°C in atmospheres with and without water vapour

“…31 A major problem in interpreting the results on the basis of point defects is that chromia growth is claimed to be dominated by grain boundary rather than lattice transport. 3,23 In explaining experimental observations, some authors 3,23,26 assumed that classical defect equilibria related to an oxide lattice are applicable for describing transport processes along grain boundaries, however, it has not yet unequivocally been demonstrated that this is indeed the case.…”

“…This may occur as a result of different types and/or concentrations of point defects in the two sublayers and/or due to large differences in densities of grain boundaries which will affect the overall ion transport as grain boundaries are known to be preferred diffusion paths in chromia scales at the prevailing temperature. 3,23 The formation of voids will reduce the area available for diffusion of the mobile species in the scale and will thus result in a decrease of the scale growth rate. This may be the explanation for the observed decrease in the weight gain rate in the thermogravimetric studies after switching the gas from the dry to the wet gas (Fig.…”