Determination of steep stress gradients by X-ray diffraction — results of a joint investigation

Stresses caused by surface treatments show principally a profile versus the depth beneath the surface. The stress profile may be very steep near the surface, in which case the methods of its determination are restricted to those using X-ray diffraction. Various methods of stress gradient determination are known using layer removal or determining the profile from measurements at the original surface. The evaluation procedures are very susceptive to the accuracy of the measurements, especially when gradients are steep. Recommendations for measurement parameters and for the evaluation of steep stress gradients should be assessed. This was the reason to initiate this joint task to study very steep gradients and to elaborate respective recommendations. Participants came from several universities, research institutes and from industry. Two sets of identically treated specimens were produced and studied at the different institutions. Case hardened and subsequently ground samples of 16MnCr5 steel and ground samples of Si3N4 ceramic material were chosen. One special set of lattice-strain distributions has been evaluated by several participants to compare and test the procedures of stress gradient evaluation that are used by the different institutions. Recommendations are given for the procedure of measurement and evaluation to determine steep stress gradients from measurement at the original surface.