Determination of Residual Stress Fields in a Thermally Grown Oxide under Thermal Cycling Loadings, Using XRD and Raman Spectroscopy — Correlations with Microstructural States

Abstract

Abstract. The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed. IntroductionNiCr alloys are currently used at high temperatures because it develops a dense chromia surface oxide film which slows down the oxidation process. In turn, the material durability depends on the ceramic film integrity. The isothermal oxide layer growth or the cooling steps usually induce the development of high residual stress in the ceramic film. The determination of such growth or residual stress has already been undertaken [1][2][3][4][5][6][7]. And subsequent stress release may induce buckling or spalling phenomena which will renew oxidation of the metallic alloy [8][9][10]. In addition, stress release may also proceed by creep which should be less detrimental for the system. This behaviour has been suggested by [2,11] from growth stress evolution measurements in Ni30Cr alloys. In order to increase the durability of chromia forming alloys, it is mandatory to better understand such stress build up and relaxation mechanisms. The aim of the present work is a first attempt to evaluate quantitatively the stress release processes in Ni-30Cr alloys. To this end, in addition to stress evaluation, the delamination rates (buckling and spalling) will be determined. The influence of different metallurgical parameters (cooling rate, oxidation temperature and duration) which in turn modify the microstructure, will also be investigated.