The gradual development of microstructure is inherently characteristic for nanocrystalline thin films. It is controlled by competitive growth of adjacent grains and is responsible for the development of depth gradients of stresses if the structure develops from fine at the film/substrate interface to coarse in the film bulk [1]. Film growth is, however, typically also accompanied by the evolution of texture as the preferential orientation of grains may change in the course of film development as a consequence of competitive atomistic processes on the surface of the growing film. This phenomenon has been reported for almost every transition metal nitride thin film material [2, 3]. As soon as the change of the grain size during growth of nanocrystalline films is accompanied with a change of texture, it is not possible to isolate the effect of the individual phenomena on the development of residual stresses. The knowledge of the origin of stress gradients in thin films is, however, crucial in controlling the stress state of these materials. Thus, we discuss in this paper the exclusive effect of the grain size on the development of stress gradients in thin nanocrystalline films irrespective of the film texture. As examples, the stress gradients in TiN films having exclusively either (111) or (100) texture were studied. The effect of the varying film texture on the development of stress gradients is further discussed for TiN films exhibiting a crossover of texture from (100) to (111) with increasing thickness. As an evidence of the depth gradients of stresses in strongly textured film materials, stress measurements of the cross-section of a TiN(100) film by spatially resolved synchrotron nanodiffraction experiments is given. It will be shown that the development of stress gradients in nanocrystalline films is predominantly given by the variation of the grain size, whereas the contribution of the texture changes has only a minor effect.

[1] R. Daniel, K.J. Martinschitz, J. Keckes, C. Mitterer, Acta Mat. 58 (2010) 2621-2633.

[2] J.E. Greene, J.-E. Sundgren, L. Hultman, I. Petrov, D. B. Bergstrom, Appl. Phys. Lett. 67 (1995) 2928-2930.

[3] I. Petrov, P.B. Barna, L. Hultman, J.E. Greene, J. Vac. Sci. Technol. A 21 (2003) 117-128.

The CrZrSiN coatings were deposited on Si wafer and tungsten carbide substrates by cathodic arc deposition system using CrZr target and tetramethylsilane gas. The tetramethylsilane gas flow rate was adjusted to fabricate the CrZrSiN coatings with different silicon contents. The crystalline structure of coatings was measured by a glancing angle X-ray diffractometer. Microstructures of thin films were examined by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) , respectively. The hardness, adhesion and tribological properties of thin films were measured by nanoindentation, scratch tester and ball-on-disk wear tests. It was found that the micro structure and mechanical properties were strongly influenced by the tetramethylsilane gas flow rate and Si content of the CrZrSiN thin films. The optimal silicon content for the Cr ZrSiN coating was proposed in this study.

Toughness is one of the most important mechanical properties of protective thin films, especially those under erosive environments. In this paper, a method is presented for measuring the fracture toughness of hard coatings. Pre-cracked micro double cantilever beams of the coatings are fabricated using focused ion beam, which are subsequently compressed by nanoindentation with a flat diamond punch. The compression exerts a bending moment on the cantilever beams causing the pre- cracks to grow. Thus, the fracture toughness of the coating can be determined as a function of the compression load at the point of crack elongation. Crack growth has been studied experimentally and compared with FE simulations to evaluate effects such as friction between indenter tip and coating surface. This method has been demonstrated using materials of known toughness and found to be useful for materials with a large yield stress to toughness ratio. Finally, this technique was applied to determine the fracture toughness of different PVD hard coatings, which will also be compared and discussed here.

Cubic (c)- Ti_1-xAl_xN coatings are unstable and isostructurally decompose to c-TiN and c-AlN at elevated temperature for compositions inside the spinodal. Both theoretical and e xperimental studies of this alloy have revealed the detailed characteristics of this decomposition. However, a the details of the early stage spinodal decomposition behavior and the resulting microstructure of Ti_1-xAl_xN /TiN multilayers remains unclear . Such study is of interest since the kinetics of the spinodal decomposition is seen to differ compared to monolithic TiAlN. The characteristic of an interface-controlled decomposition is the formation of a layered microstructure parallel to the interface, i.e. surface directed spinodal decomposition (SDSD). If present in TiAlN/TiN layers it could explain the improved high temperature properties observed in these multilayers. Hence, in this study we investigate if SDSD is present in arc evaporated c-Ti_0.33Al_0.67N/TiN and c-Ti_0.50Al_0.50N/TiN coatings and discuss the prerequisites for such decomposition.

We have used DSC, XRD, STEM/TEM-EDX, and 3D atom probe tomography (APT) in combination with 2D phase field simulations to understand the decomposed morphology and the decomposition kinetics. The annealing procedure was chosen such that the spinodal decomposition was at an early stage, i.e. annealing at 700-900 °C with no isothermal period. DSC revealed that the isostructural spinodal decomposition, to c-AlN and c-TiN, in the multilayers has the same onset temperature regardless of composition. The onset is located ~100 °C lower compared to the monolithic coatings. Z-contrast STEM imaging confirms this by showing a decomposed structure of the multilayers at a temperature where it is not present in the monoliths. The APT shows an evolving AlN-rich layer followed by enrichment in TiN at the interfaces in the decomposed state. The phase field simulations also predict such SDSD. The simulations further show that the decrease of the total energy transpires over a longer time period in the multilayers compared to monoliths due to the SDSD. This is in line with the thermograms showing a broader spinodal decomposition peaks from the multilayers. We also note that the microstructure resulting from SDSD in TiAlN is highly dependent on the growth induced elemental fluctuations. The decomposition behavior of the coatings is discussed in terms of internal interfaces, elemental fluctuations, coherency stresses, and alloy composition. Understanding and controlling the evolving microstructure and the onset of the spinodal decomposition by interface architecturing, may facilitate optimization of the cutting performance of TiAlN coatings.