Arnold C. Vermeulen

Applicabilities of the Warren-Averbach Analysis and an Alternative Analysis for Separation of Size and Strain Broadening

The validities of the Warren–Averbach analysis and of an alternative analysis for separation of size and strain contributions to diffraction line broadening are investigated. The analyses are applied to simulated and experimental line profiles. The Fourier coefficients of the simulated line profiles are derived from expressions for the distortion field around specific lattice defects: misfitting inclusions and small-angle grain boundaries. Applicability tests are also performed on experimental powder diffraction line profiles taken from plastically deformed specimens: thin aluminium layers and ball-milled molybdenum powders. It is concluded that for both methods finite but different classes of specimen exist for which they give meaningful results. In practice, each time an analysis is performed the results must be tested against common (physical) sense and all information available on the specimens.

The Sensitivity of Focusing, Parallel Beam and Mixed Optics to Alignment Errors in XRD Residual Stress Measurements

The sensitivity of various combinations of optics to alignment errors is investigated. A large number of tests with varying specimen displacements and incident beam misalignments are performed for both line and point focus residual stress optics combinations. This investigation includes experiments with mixed combinations of typical “focusing beam optics” and “parallel beam optics”. It is verified if the peak positions are either sensitive to height errors like for the focusing beam geometry or insensitive like for the parallel beam geometry. The peak position sensitivity is classified for all combinations of incident beam and diffracted beam optics modules.

Data collection requirements for the analysis of residual stress in polycrystalline coatings

Residual stress in polycrystalline coatings can be determined by X-ray diffraction. The data collection requirements are summarized and evaluated in this paper. First, general requirements for stress measurements are described. Then, requirements related to the diffraction geometry and the specimen manipulation are considered. Finally, requirements with respect to specimen characteristics, including various coating-substrate combinations are presented. Polycrystalline coatings can be nanocrystalline, randomly orientated or highly textured. The substrates can be of any nature: amorphous, polycrystalline or single crystal. The complete set of requirements leads to a measurement advice for a particular coatingsubstrate specimen, which includes the choice of diffraction geometry and the data collection strategy. Based on two complementary test cases it is demonstrated that the set of rules is complete and that they can be applied to any type of polycrystalline specimen.

Alignment of a ¼-Circle Cradle for Reliable Residual Stress Measurements

The alignment of a ¼-circle Eulerian cradle is discussed. The method is based on diffraction and uses a special alignment tool and a stress-free powder sample. A new profile shape function is introduced to describe better distorted diffraction peaks.