Diffraction stress analysis of highly planar-faulted, macroscopically elastically anisotropic thin films and application to tensilely loaded nanocrystalline Ni and Ni(W)

The presence of planar faults complicates the diffraction stress analysis enormously owing to fault-induced displacement, broadening and asymmetry of the Bragg reflections. A dedicated stress-analysis method has been developed for highly planar-faulted, fibre-textured thin films of cubic crystal symmetry, using only specific reflections for diffraction stress analysis. The effect of unjustified use of other reflections has been demonstrated in the course of application of the method to Ni and Ni(W) thin films exhibiting excessive faulting and subjected to (1) a planar, rotationally symmetric stress state and (2) a planar biaxial stress state. In case 1 the crystallite-group method has been used, whereas in case 2 the stress-analysis method based on X-ray stress factors had to be applied. The successful separation of stress- and fault-induced reflection displacements has enabled the investigation of the mechanical behaviour of Ni and Ni(W) thin films by in situ stress measurements during tensile loading, thereby exposing pronounced stiffness and increased strength by alloying with W.