W.G. Sloof

Diffraction analysis of nonuniform stresses in surface layers : Application to cracked TiN coatings chemically vapor deposited on Mo

Variations of residual stresses in layers on substrates can occur in directions parallel and perpendicular to the surface as a result of compositional inhomogeneity and/or porosity or cracks. Diffraction methods to evaluate such stress variations are presented. Comparison of the experimental value for the stress with a calculated value of the “diffraction-averaged stress,” on the basis of a model for the local stresses, proved to be a useful method of stress analysis. It is shown that a direct evaluation of occurring stress-depth profiles is less practical. The method of stress analysis proposed, is applied to chemically vapor deposited TiN coatings on Mo substrates. In these coatings a large tensile stress parallel to the surface develops during cooling from the deposition temperature, due to difference in thermal shrink between coating and substrate. As a result of the cooling-induced stress, cracking of the coating occurs. The mesh width of the crack pattern allows determination of the fracture-surface energy and the fracture toughness of the coating material. Conceiving the cracked coatings as assemblies of freestanding columns, and assuming full elastic accommodation of the thermal mismatch at the column/substrate interface, the stress variations in the coating are calculated. On this basis the diffraction-averaged stress and the depth profile of the laterally averaged stress can be predicted accurately for the cracked TiN layers.

Hard dense CrNx coatings on three-dimensional objects

Abstract Thin CrNx coatings were deposited on steel in an industrial, Hauzer HC 750 PVD machine equipped with a bucket plasma source. The microstructure, deposition rate and chemical composition of the deposited coatings all depend on the applied bias voltage, the nitrogen flow and the deposition temperature. The results show a constant high hardness and Youngs modulus for applied bias voltages above 50 V. Remarkably, the composition of the coating has only a small influence on the hardness and modulus. It was found that high hardness and high density correlate very well.

Composition, microstructure, and properties of crystalline molybdenum silicide thin films produced by annealing of amorphous Mo/Si multilayers

Amorphous Mo/Si multilayers were prepared by alternately sputtering Mo and Si onto silicon single‐crystal substrates covered with SiO2 and onto substrates covered with polycrystalline Si. The multilayer thickness was about 200 nm and the composition modulation period was about 0.8 nm. The Mo/Si atomic ratio averaged over the multilayer was about 0.6. These specimens were isochronally annealed for 1 h at temperatures up to 1000u2009°C. In order to analyze annealing‐induced variations in composition, microstructure, resistivity, and internal stresses, the specimens were investigated by x‐ray diffractometry, Rutherford backscattering spectroscopy, and resistometry. Although the multilayer remained amorphous during annealing at temperatures below 350u2009°C, interdiffusion of Mo and Si occurred. Above 350u2009°C the layered structure disappeared and crystalline phases, viz., hexagonal MoSi2, Mo5Si3, and tetragonal MoSi2, appeared successively for increasing temperatures. According to the (equilibrium) phase diagram both ...

Development and partial relaxation of internal stresses in thin TiC layers chemically vapour deposited on Fe-C substrates

TiC layers were chemically vapour deposited at 1273 K mn Fe-C substrates with carbon contents between 0.06 and 1.20w%C. X-ray diffraction stress analyses showed that large compressive stresses are present in the IC coatings and that small tensile stresses any present in the substrates. The stresses developed during cooling from the deposition temperature to room temperature, owing to the difference in thermal shrink between coating and substrate. However, stress relaxation was also evident. This was provoked by the phase transformation processes occuring in the substrate on cooling. Stress relaxation was hindered when grain-boundary cementite formed in the substrates. The stresses present in the TiC coatings on substrates without grain-boundary cementite can be predicted quantitatively.

Chemical constitution and microstructure of TiCx coatings chemically vapour deposited on Fe-C substrates; effects of iron and chromium

TiCx coatings were chemically vapour deposited in an industrial reactor on Fe-C substrates with carbon contents between 0.06 and 1.20 wt % C. Electron probe microanalyses showed that significant amounts of chromium and iron were present in the coatings and that chromium was also present in the substrate region adjacent to the coatings. By comparing calculated and measured lattice parameters (corrected for the internal stresses present) it became evident that the chromium was in solid solution in TiCx, whereas the iron was not. This was confirmed by micro Auger electron spectroscopy and X-ray diffraction phase analyses. The carbon to metal ratio,x, of the TiCx coatings decreased with increasing distance to the coating/substrate interface. The effect of iron on the X-ray diffraction line broadening and hardness of the coatings was large (in contrast with the effect of chromium) and increased with increasing distance to the coating/substrate interface because of a decreasing iron particle size. The TiCx crystallite size was small and constant throughout the thickness of the coatings. The chromium present in the substrate region adjacent to the TiCx coatings influenced the microstructure of the substrate by formation of iron, chromium-carbides and reduced the growth rate of the coatings.

Evaluation of Residual Stresses in Noncompact Surface Layers

A formulation of the ‘overall’ (effective) state of stress and an interpretation of diffraction strain data are given for noncompact materials. For surface layers subjected to strains of rotational symmetry with respect to the surface normal, the ‘overall’ state of stress can be described by a stress parallel and a stress perpendicular to the surface. Determination of such stresses and their gradients is illustrated for Y-Fe4N1-x and TiN surface layers.

Development of modern analysis techniques for characterization and testing of coatings

Abstract This paper presents some developments in methods and techniques for the analysis of deposited materials. These concern X-ray diffraction, electron probe microanalysis, X-ray photo-electron spectroscopy and soft X-ray emission spectroscopy.