Klaus J. Martinschitz

Texture development in polycrystalline CrN coatings: the role of growth conditions and a Cr interlayer

The control of the texture of transition-metal nitride coatings by varying the energy of incident ions and the coating thickness and by introducing a highly textured interlayer was demonstrated on polycrystalline CrN coatings grown by reactive magnetron sputtering. Development of the preferred (1 1 1) orientation was observed at moderate ion bombardment as the adatom net flux from the (2 0 0) to (1 1 1)-oriented grains dominated. A reversal of this flux at higher ion energies associated with collisional dissociation of ions at the film surface resulted in the development of a (2 0 0) texture. Coatings composed of grains with mixed (2 0 0) and (2 2 0) orientations were developed under intense ion bombardment due to preferential re-sputtering. The preferred orientation also changes with increasing coating thickness from (2 0 0) towards (1 1 1) through competitive growth. In contrast, a complete (2 0 0)-oriented structure of the CrN layer is formed when it is grown on a Cr interlayer with strong preferred (2 0 0) orientation.

Rapid determination of stress factors and absolute residual stresses in thin films

A methodology is presented that allows the determination of experimental stress factors in thin films on the basis of static diffraction measurements. The approach relies on the characterization of thin films deposited on a monocrystalline substrate serving as a mechanical sensor. Rocking-curve measurements of the symmetrical reflections of the substrate are used to determine the substrate curvature and subsequently the macroscopic stress imposed on the film. The elastic strain in the film is determined by lattice-spacing measurement at different sample tilt angles. The calculated experimental stress factors are applied to thin films deposited on other types of substrates and are used to determine the absolute magnitude of the residual stress. The approach is applied to nanocrystalline TiN and CrN thin films deposited on Si(100) and steel substrates, characterized using a laboratory-type θ/θ goniometer.

X-ray elastic constants determined by the combination of sin2 ψ and substrate-curvature methods

Abstract A new methodology is presented that allows the quantification of experimental X-ray elastic constants of polycrystalline thin films without use of special diffractometer attachments. The approach is based on the combination of sin2 ψ and curvature methods. The elastic strains in the polycrystalline films are characterized by the measurement of lattice spacings at different sample tilt angles, while the macroscopic stress in the film is calculated from the substrate curvature applying the Stoney formula. The radius of the curvature is determined from a sequence of rocking curves measured at different sample positions. The method is demonstrated on Al thin films deposited on Si(100) substrates. The X-ray diffraction measurements were performed at the synchrotron source BESSY in Berlin.

High-temperature residual stresses in thin films characterized by x-ray diffraction substrate curvature method

A new x-ray technique to determine temperature dependencies of macroscopic stresses in thin films by characterizing the substrate curvature is introduced. The technique is demonstrated on polycrystalline TiN and Al thin films deposited on Si(100) wafers. The structures are thermally cycled in the temperature range of 25-400 degrees C using a newly developed heating chamber attached to a commercial x-ray diffractometer. The curvature of the freestanding samples was determined by the rocking curve measurement of substrate Si 400 reflections at different lateral positions of the samples, and the stresses are calculated using Stoneys formula. The results show that the magnitude of the stress is in good agreement with the results obtained by other techniques. For the practical application of the technique, the sample mounting and the temperature control are of great importance.

Temperature Dependence of Residual Stress Gradients in Shot-Peened Steel Coated with CrN

A temperature behaviour of residual stresses in shot-peened steel coated with 3m CrN is characterized using in-situ energy dispersive synchrotron X-ray diffraction performed in the temperature range of 25-800°C. The samples are thermally cycled and the development of volumeaveraged residual stresses in the coating and residual stress depth gradients in the steel is characterized. The results reveal complex changes of stresses in CrN and in the substrate. The annealing results in the removal of stress gradients in the steel which starts at the temperature of about 600°C. After cooling down, there are no stresses detected in the steel. The temperature dependence of stresses in CrN is very complex and indicates the presence of phenomena like an annealing of intrinsic stresses about the deposition temperature of 350°C, a formation and a closing of micro-cracks in the tensile region and finally a stress relaxation of approximately 500 MPa after the cooling down. The presented approach allows a complex characterization of thermo-mechanical processes in coating-substrate composites and opens the possibility to understand phenomena related to the thermal fatigue of coated tools.

Stress Factors and Absolute Residual Stresses in Thin Films Determined by the Combination of Curvature and sin²ψ Methods

A new method is presented which allows the determination of experimental stress factors in anisotropic thin films on the basis of static diffraction measurement. The method is based on the simultaneous characterization of macroscopic stress and elastic strain in thin film using substrate curvature and sin2ψ methods, respectively. The curvature of monocrystalline substrate with known mechanical properties is determined using rocking curve measurements on substrate symmetrical reflections. The experimental stress and strain values are used to calculate stress factors for the specific film as a function sample tilt angle and reflection measured. The approach represents a relatively simple recipe to determine residual stress magnitude in thin films on the absolute scale. The procedure is demonstrated on polycrystalline Cu thin film deposited on Si(100).