Am. Huntz et al., EVIDENCE OF STRESS-RELAXATION IN THERMALLY GROWN OXIDE LAYERS - EXPERIMENTS AND MODELING, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 248(1-2), 1998, pp. 44-55
High temperature X-ray diffraction was used for determining the stress
es created in chromia layers formed on Ni-Cr as a function of various
parameters: substrate and oxide layer thickness, grain size, yttrium d
oping, cooling rate. After oxidation, stresses at room temperature in
the oxide layer are compressive. During further heating, their values
decrease with annealing temperature and they tend to zero at 900 degre
es C, indicating that the oxide growth stresses are negligible. Beside
s, relaxation phenomena were experimentally evidenced during heat-trea
tments after previous oxidation. A numerical model was developed to ca
lculate the stress and the relaxation phenomena. It takes into account
the mechanical behaviour of both the substrate and the oxide, and par
ameters such as substrate thickness, oxide grain size, cooling rate or
heat-treatment duration, etc. This elasto-visco-plastic model correla
tes the experimental results with the various parameters of the study
and agrees with previous results obtained for NiO layers. Finally, usi
ng a finite element model, it was shown that the stress gradient in th
e oxide is negligible. (C) 1998 Elsevier Science S.A. All rights reser
ved.