High-precision determination of residual stress of polycrystalline coatings using optimised XRD-sin2ψ technique

The aim of the research is to optimise the XRD-sin2ψ technique in order to perform high precision measurement of surface residual stress. Residual stresses existing in most hard coatings have significant influence on the adhesion, mechanical properties and tribological performance. In the XRD-sin2ψ stress measurement, the residual stress value is determined through a linear regression between two parameters derived from experimentally measured diffraction angle (2θ). Thus, the precision coefficient (R2) of the linear regression reflects the accuracy of the stress measurement, which depends strongly on how precise the 2θ values are measured out of a group of very broad diffraction peaks. In this research, XRD experiments were conducted on a number of samples, including an electron beam evaporated ZrO2 based thermal barrier coating, several magnetron sputtered transitionmetal nitride coatings, and shot-peened superalloy components. In each case, the diffraction peak position was determined using different methods, namely, the maximum intensity (Imax) method, the middle point of half maximum (MPHM) intensity method, the gravity centre method, and the parabolic approaching method. The results reveal that the R2 values varied between 0.25 and 0.99, depending on both the tested materials and the method of the 2θ value determination. The parabolic approaching method showed the best linear regression with R2=0.93±0.07, leading to high precision of the determined residual stress value in all cases; both the MPHM (R2=0.86±0.16) and gravity centre (R2=0.91±0.11) methods also gave good results in most cases; and the Imax method (R2=0.71±0.27) exhibited substantial uncertainty depending on the nature of individual XRD scans

Effect of the degree of high power impulse magnetron sputtering utilisation on the structure and properties of TiN films

TiN films were deposited using high power impulse magnetron sputtering (HIPIMS) enabled four cathode industrial size coating system equipped with HIPIMS power supplies. The standard version of this system allows control over the ion bombardment during coating growth by varying the strength of the electromagnetic field of the unbalancing coils and bias voltage applied to the substrate. The coatings were produced in different coating growth conditions achieved in combined HIPIMS — direct current (dc) unbalanced magnetron sputtering (HIPIMS/UBM) processes where HIPIMS was used as an additional tool to manipulate the ionisation degree in the plasma. Four cathode combinations were explored with increasing contribution of HIPIMS namely 4UBM (pure UBM), 1HIPIMS + 3UBM, 2HIPIMS + 2UBM and 2HIPIMS (pure HIPIMS) to deposit TiN coatings. Optical emission spectroscopy (OES) measurements were carried out to examine the plasma generated by the various combinations of HIPIMS and UBM cathodes. The micro-structural study was done by scanning electron microscopy (SEM). X-ray diffraction (XRD) technique was used to calculate the residual stress and texture parameter. It has been revealed that the residual stress can be controlled in a wide range from − 0.22 GPa to − 11.67 GPa by intelligent selection of the degree of HIPIMS utilisation, strength of the electromagnetic field of the unbalancing coils and the bias voltage applied to the substrate while maintaining the stoichiometry of the coatings. The effect of the degree of HIPIMS utilisation on the microstructure, texture and residual stress is discussed. Combining HIPIMS with dc-UBM sputtering is also seen as an effective tool for improving the productivity of the deposition process

Stress in and texture of PVD deposited metal nitride films

Thin metal nitride films deposited by Physical Vapor Deposition (PVD) are used amongst many other applications as wear protective coatings in tool industry or as diffusion barriers in integrated circuit technology. Typically these films exhibit a residual in-plane stress when deposited onto rigid substrates such as silicon wafers or cutting tools. This stress influences the performance of the films in application: too high compressive stress will cause buckling of the film; too high tensile stress will promote cracking of the film under load. Both consequences are undesirable in the application of the thin film. The aim of this thesis is to extend the knowledge on the influence of deposition parameters on the characteristics of metal nitride thin films deposited by magnetron sputtering, a commonly employed PVD technique. More specifically the correlation of the generation of film stress and the crystallographic texture of thin titanium nitride films is studied.Material Science and EngineeringMechanical, Maritime and Materials Engineerin

DESIGN, ANALYSIS AND MANUFACTURING OF A THERMOPLASTIC UD CF-PEEK SLAT

Composite structures are increasingly being used within aircrafts, but not within impact endangered areas. In co-operation with DLR and EADS IW, a new advanced thermoplastic composite slat concept, based on the aerodynamic shape of an A340 outer slat, had been developed with the aim of minimizing weight and manufacturing costs

Design, analysis, and manufacturing of a carbon-fibre-reinforced polyetheretherketone slat

Composite structures are increasingly being used in aircraft applications. Regarding Airliners, the application of composites within impact endangered areas is unusual. In cooperation with DLR - Institute of Structures and Design and EADS - Innovation Works, an advanced thermoplastic composite slat, based on an aluminum A340-600 outer slat, had been developed with the aim of minimizing weight and manufacturing costs in series production. The investigation of many manufacturing techniques had been performed as well as integration of new materials. Several generic and full scale thermoplastic demonstrators were manufactured, using endless fiber reinforced CF-PEEK. The critical point, concerning the casting of thick and highly tapered, single curved thermoplastic shells, was identified and new manufacturing methods had been developed. Additionally, the thermoplastic welding process was improved, resulting in a low cost assembly technique as alternative to state-of-the-art joining methods such as riveting. In addition to conventional linear static analysis, dynamic high velocity impact simulations were carried out. A numerical approach for high velocity bird strike impact had been developed. The results were used to dimension the residual strength of a damaged slat. Furthermore, a good compliance between the dynamic analysis and the performed tests has been reached. It has been shown, that a significant weight reduction is possible by numerical optimization, even if brittle materials as composites are used for impact sensitive areas. The verification of the impact performance for high performance thermoplastic materials had been demonstrated as well as the possibility of manufacturing skins of complex geometry, using out-of-autoclave manufacturing methods. Existent welding methods had been adapted to usage with endless carbon fiber reinforced CF-PEEK

Stress and texture in HIPIMS TiN thin films

Titanium nitride (TiN) films in the thickness range of 0.013 mu m to 0.3 pm were grown by high power impulse magnetron sputtering (HIPIMS) on silicon substrates in two deposition modes: a) the substrate was grounded and b) - 125 V bias was applied to the substrate. On the films we performed microstructure-, film texture- and film stress-analysis. The films deposited under - 125 V bias experienced a more energetic ion bombardment than the films deposited on grounded substrates. This difference in ion bombardment energy is reflected in the different microstructure. In contrast to previous results for TiN films grown by conventional reactive magnetron sputtering, we observe no major film stress gradient for increasing film thicknesses. We explain this observation from the absence of a 200-to-111 texture crossover during film growth. A moderate ion bombardment leads to TiN films with (111) texture. while an intense ion bombardment leads to films with (001) texture (Greene et all.: Appl. Phys. Lett. 67 (20) 2928-2930 (1995)). At the same time (001) oriented grains are much more susceptible to compressive stress generation by ion bombardment than (111) oriented grains. (C) 2009 Elsevier B.V. All rights reserved