Residual stresses exist in all solids. They result from mechanical or chemical phenomena. At the moment, physico-chemical researchers are starting to pay attention to the part played, in surface reaction, by these stresses developed a few microns below the sample surface, in crystallized materials. X-ray diffraction is a privileged tool for investigating this domain. Measurements are carried out by using sin$^{2}\psi$ technics [1,2].
Such determinations can be obtained as post-reactional events; i.e. the reaction being achieved is brought back to ambient temperature under standard atmosphere. This is a classical way to determine the residual stresses developed by thermal treatments or welding. However, as residual stresses can result in cooling down, if one is dealing with the role of stresses on the reaction mechanisms, "in-situ" measurements are of basic interest.
According to the above point, we developed a high temperature, controlled atmosphere device especially built for residual stress investigations by X-ray diffraction. This apparatus was built at the laboratory "Ractivit‚ des Solides" [3]. The basic goal for realising such a chamber was, first, to place the sample under thermal equilibrium with a heating spherical cavity of sufficient volume to ensure that the whole sample would not undergo a temperature - gradient greater than 1$^{o}$C at 1000$^{o}$C. Secondly, it was important for the positioning accuracy not to be modified by temperature dilatation of more than 0.1 mm between ambient temperature and 1200$^{o}$C.
This paper describes a device dedicated to studying, by X-ray diffraction the residual stresses developed on surface samples as a function of temperature and atmosphere conditions.
1. G.MARDER, J.L. LEBRUN, J.M. SPRAUEL, Matriaux et
Techniques (Avril-mai
1981) p135.-139.
2. G.MAEDER, Chemica Scripta, 26A (1986) p23-31.
3. F.BERNARD, thesis, University of Burgundy (1993).