Equi-penetration grazing incidence X-ray diffraction method: Stress depth profiling of ground silicon nitride

In this work a new modification of the grazing incidence X-ray diffraction method for residual stress determination is presented. This equi-penetration grazing incidence X-ray diffraction method is especially suitable for the precise determination of the residual stress depth profile in materials. It originates from a sin2ψ approach based on the determination of the lattice spacing of various selected diffraction planes. Additionally, for each measurement the condition ∂τ/∂ψ = 0 is here fulfilled and one dataset corresponds strictly to a specific mean penetration depth τ independent of the tilt angle ψ. This can be achieved by the individual adjustment of the incidence angle for each measured diffraction maximum. In the actual work, the influence of different surface finishes on the stress depth profile of commercial silicon nitride ceramic samples is investigated. The ground specimen displays an almost biaxial compressive stress parallel and near to the specimen surface of 3 GPa, which decreases almost up to zero in a depth of 5 μm. After the polishing process, the specimens show a strongly reduced compressive stress maximum at the surface of 1 GPa, which diminishes similarly with increasing depth. The orientation between the stress component and the grinding direction is of minor influence. Furthermore, the influence of a possible residual stress component perpendicular to the sample surface is discussed.