科研之友
微信
新浪微博
Facebook
分享链接
摘要
The paper contains results of studies on X-ray diffraction analysis XRD (studying the phase composition, crystallite sizes and lattice deformations) of oxide layers on P91 steel, operated for a long time at an elevated temperature (T = 535 degrees C, t = 70,000 h). X-ray studies were carried out on the inner surface of a tube, and then the layer surface was polished down to 3.5 mu m and the diffraction measurements were performed again to determine individual oxide layers. It has been found that a three-zone oxide layer is formed as a result of long-term operation of P91 steel at the temperature of 535 degrees C. Hematite occurs on the inner surface of the tube. Then magnetite appears below hematite. Going deeper into the layer there is a spinel, i.e. a mixture of magnetite and chromite. A visible decay of total intensity for Fe2O3 is observed already at the polishing depth of 3.5 mu m. In the case of Fe3O4 and FeCr2O4 an increase in total intensity is observed already from 7 mu m, what manifests in narrowing the diffraction line and hence in increasing the crystallites size and in the relaxation of stresses in this oxide layer. The broadening of a diffraction line caused by a small size of crystallites is expressed by the Scherrer relationship. Instead, the beta(z) broadening resulting from lattice distortions (relaxation of stresses) was determined from the Taylor relationship.
- 出版日期2013
