No abstract

An Inconel Alloy 600 C-ring was subjected to various strain levels and the deformation process was monitored by a Computer Aided Rocking Curve Analyzer (CARCA). A large grain population was sampled, and the calibration curve of average rocking curve halfwidth of the individual grains relating to the nominal strain was established. The strain distribution as a function of the angular position along the peripheral surface layer and layers at different depth distance was obtained. Up to C-ring closure at the nominal strain of 3.3% at the apex, the induced plastic strains were confined to a surface layer of 30–40 gm in depth.The largest strain and strain gradients below the surface occurred at the apex and near apex region. The extent and the spread of microdeformation inhomogeneity increased with applied strain. At ring closure some grains exhibited large plastic strains while others exhibited only small plastic strains or were not affected by the deformation process at all. These experimental results were not in agreement with the current theoretical understanding of the deformation of C-ring since these theories did not take shape changes into account. When such changes were included, good agreement on the angular strain dependence for the apex and near apex region were achieved between experiment and theory. It was concluded that the CARCA X-ray method can be a useful research tool in aiding and guiding mathematical modeling of non-linear inelastic behavior of solids by disclosing important microstructural and micromechanical aspects.

No abstract

The aim of this investigation was the establishment of a quantitative link between micro and macrodeformation and kinetic recovery of nickel-base Alloy 600 as well as the early detection of microcracks in this alloy when exposed to stress corrosion. To reach these objectives, X-ray rocking-curve measurements were carried out using the method known by its acronym CARCA (computer-aided rocking-curve analysis). Supported by transmission electron microscopy, a calibration curve was established relating dislocation density, X-ray rocking-curve halfwidth and strain. Applying CARCA, deformation levels and work-hardening characteristics of the alloys were measured by quantitative characterization of the induced defect structure. By correlating the analysis of the defect structure to the kinetic recovery of the alloys, including determination of the activation energies, it was possible to infer from the thermal stability of the alloys the dislocation obstacles responsible for hardening at different strain levels. It was shown that the recovery of the alloys was conditioned by their low stackingfault energy and that it depended on the strain level. Rapid recovery associated with grain boundary diffusion occurred at very small plastic strains up to about 0.7% with measured activation energies of recovery of about 25.6 Kcal/mol. At higher strains bulk diffusion was necessary to overcome the obstacles by dislocation climb with Q — 67 kcal/mol, The CARCA method proved itself to be a valuable research tool for assessing quantitatively the defect density and the mechanically and thermally induced changes. Relaxation effects, recorded by CARCA in the apex region of stressed C-rings exposed to a caustic medium, may open a path for early nondestructive detection of microcracks in stress-corrosion cracking.