X-ray investigation of stress measurement on heat resisting materials

The elastic constants of nickel base alloy at high temperatures were studied by the X-ray method with a new apparatus consisting of a horizontal type tensile testing machine and a vacuum furnace. Residual stresses due to precipitation hardening were also studied. In connection with the above experiments, the authors performed the observations of microstructure of the material at various temperatures. After the heat treatment for precipitation hardening, all the plate specimens of Inconel Xwere finished and then electropolished before being exposed to X-ray. The characteristic X-ray of CrKβ was irradiated on them through a thin beryllium foil, and the strain was determined by measuring the diffraction from (311) atomic plane by means of the conventional sin2psi diagrams using counter technique. The conclusions obtained are as follows. (1) The elastic constants of Inconel X obtained by the X-ray technique are in good agreement with those measured mechanically within the experimental errors. The values obtained, however, decrease slightly more with temperature. (2) The lattice spacings or lattice constants changed about 5.2 degree in 2theta from room temperature to 923 K. Consequently, it is necessary to take great care of slight change in temperature for stress measurement by X-ray. (3) For precipitation hardened Inconel X, the compressive residual stress is generated on the surface and remains from room temperature to about 700 K. (author)