Harri Lille

Determination of Residual Stresses in Thermal and Cold Sprayed Coatings by the Hole-Drilling Method

Residual stresses in most coatings have a significant influence on adhesion, on mechanical properties and on tribological performance. Residual stress can not be measured directly, rather strain is measured and stress is calculated. In this study residual stresses were investigated in thick thermal Ni95Al5 and cold sprayed Ni, Cu, NiZn, AlZn powder coatings using the semi-destructive hole-drilling and layer growing curvature methods. Residual stresses obtained for the thermal spray coating were compressive and with a relatively large deviation of the results indicating the nonuniformity of residual stress. Cold sprayed coatings have more uniform structure than thermal sprayed coatings. Residual stresses were compressive, and results obtained by hole-drilling and curvature method were comparable.

Comparison of Curvature and X-Ray Methods for Measuring of Residual Stresses in Hard PVD Coatings

Physical Vapour Deposition and PVD coatings are designed for several applications, from industrial to biomedical. Residual stresses, arising during coating deposition, have important effect on the coating’s service life as their influence to the mechanical and tribological properties. Our aim was to investigate the residual stresses in five different PVD coatings (TiN, TiCN, TiAlN, TiAlN, nc-(AlTi) N/α -Si3N4) (presence of the Ti as adhesion layer) by the layer growing curvature method and the X-ray diffraction techniques using a plate and a strip as the substrate. Residual stresses were compressive and very large (2.98 - 7.24) GPa in all coatings and comparable in TiN, TiAlN, TiAlN coatings in the case of both methods. The magnitude of residual stresses is influenced by intrinsic strain in the case of layer growth rather than by thermal stress.

Investigation of Residual Stresses in Flame Sprayed Ni-Based Wear Resistant Coatings by the Hole-Drilling and X-Ray Methods

The present investigation was carried out in order to determine residual stresses inNi-based self-fluxing alloy based high velocity oxy-fuel (HVOF) coatings with different wearresistant additives. The main components of the alloy were Ni, Cr, Si and B. To increase the wearresistance of self-fluxing NiCrSiB alloy based coatings, different ceramics and hard metals(WC-Co, TiC-NiMo and Cr2C3-Ni) were added. Residual stresses were measured by the holedrillingmethod and the X-ray method. The incremental hole-drilling technique combined with theintegral method was applied. This combined method allows to analyse non-uniform throughthicknessresidual stresses. The results obtained with the incremental hole-drilling method indicatethat through-thickness residual stress distribution is non-uniform. The determined residual stresseswere tensile on the surface of the coating and became compressive toward the interface.The values of the modulus of elasticity and microhardness of the coatings were obtained byinstrumented indentation. The microstructures of the studied coatings were investigated with theSEM technique.

On Determination of Residual Stresses in Coatings from the Measured Longitudinal Deformation of a Strip Substrate

This paper presents an algorithm for the calculation of initial stresses from the longitudinal deformation of a straight strip substrate, measured during the simultaneous deposition or dissolution of a coating on the two sides of the substrate. The possibility of prestressing the substrate by an elastic element (spring, semiconductor) is taken into account. An example of application is presented.

A Device for Determination of Residual Stresses in Galvanic Coatings from the Measured Longitudinal Deformation of a Strip Substrate

A method was elaborated for the determination of residual stresses in the galvanic coating by measuring the longitudinal deformation of a straight strip (ribbon) and of a cylindrical (wire) substrate. For this purpose an experimental measuring system was designed. The experiments were carried out using a nickel coating deposited bilaterally from Watts electrolyte on a copper or brass strip substrate, and initial stresses were calculated. The strip substrate was fixed by one end and loaded with a calibrated weight on the other. The longitudinal displacement of the free end of substrate, depending on coating thickness, was determined by measuring the deformation of the elastic element. The effect of the rigidity of an elastic element on initial stresses was investigated. The results are compared with the literature data.

Representation of an Object as a Semiotic Sign in Engineering

The report analyses how to better proceed from general discussion on graphic literacy in engineering education, by differentiating between the different types of engineering drawings, from the semiotic point of view, which has inductive reasoning and plays an explanatory role. In the long history of visualization in engineering graphics one has gained (presented) new ideas for solving problems (Plans and architectural drawings in Ancient Egypt, http://www.ucl.ac.uk/museeums-static/digitalegypt/architecture/plans.html, [1]) and drawing is one of the oldest engineering disciplines. Real products are manufactured on the basic of engineering drawings. Engineering and technology students learn basic knowledge, in order compose engineering drawings as reflections of existing objects or concepts of future objects, within the Engineering Graphics course. The development of Engineering Graphics is influenced (besides other theories) by semiotics—the study of signs and symbols. Peirce’s triadic model can help encode and decode signs for which there international agreement that excludes different interpretations and includes the study of how meaning is constructed and understood (http://www.newworldencyclopedia.org/entery/Semiotics, [2]).

Evaluation of Residual Stresses in PVD Coatings by Means of Strip Substrate Length Variation and Curvature Method of Plate Substrate

The aim of the study was to determine macroscopic residual stresses in Physical Vapor Deposits (PVD) coatings through measurement of the length variation of the strip substrates coated on both sides. The length change of the strip was reduced to the deflection of the middle cross-section of the elastic element and was recorded by four strain gauges. For validating the obtained results, the conventional curvature method was used. As an application, residual stresses in hard AlCrN PVD coatings were investigated. The coatings were nanolayered to achieve better coating toughness for blanking and punching applications. The steel strips and steel plates with two thicknesses were used as the substrate. The values of the compressive residual stresses, determined by both methods for the investigated coatings, were very high (3.3 -3.6 GPa) independent of coating thickness and practically equal within the measurement uncertainty of the method. Good agreement between the experimental results obtained with both methods suggests that the presented method, strip length variation, is applicable for determination of residual stresses in coatings. Compressive stresses in coatings are desirable as they strengthen the coating.

Evaluation of Residual Stresses in PVD Coatings by Means of the Curvature Method of Plate

Physical Vapor Deposition (PVD) coatings are primarily designed for metal cutting tools operating in extreme machining and blanking conditions. Residual stresses arising during coating deposition exert an important effect on the service life of the coating through influencing mechanical and tribological properties and adhesion. To determine macroscopic residual stresses, the conventional curvature method was used. As an application, residual stresses in four aluminum based PVD hard coatings, i.e. AlTiN, AlTiSiN, AlCrN, and AlCrSiN, were investigated in the presence of the Ti adhesion layer. Nickel steel plates and steel plates were used as the substrate. Residual stresses were compressive and high (3.0-7.5 GPa) in all coatings. Compressive stresses in coatings are desirable in cohesive tool damage as they strengthen the coating. The values of residual stresses were not significantly dependent on the angle of plate placement (parallel (0°), inclined (45°) and perpendicular (90°)) in relation to the PVD cathode in the deposition chamber. The magnitude of residual stresses is influenced by intrinsic strain at layer growth rather than by thermal stress.

Comparative Analysis of Residual Stresses Determined by Various Methods in Brush-Plated Hard Gold and Silver Coatings

The investigated brush-plated silver and gold coatings are used for refining the surface properties of electric apparatuses. Tensile residual stresses generated in the plated coatings were determined with a thin-walled ring substrate using the curvature and instrumented indentation techniques. These stresses relax over time; the dependence of relaxation time was approximated by a linear-fractional function. The modulus of elasticity and the nanohardness of the coatings were determined by nanoindentation. The surface morphology and structure in cross-section of the coated substrates are presented.

Measurement of Residual Stresses in the Cold-Rolled Fe-Ni-Mn/Invar Thermo-Bimetallic Plate

The paper presents a method for measuring residual stresses in normal thermo-bimetal Fe-Ni-Mn/Invar strips with a thickness of 0.76 mm. For this purpose, a setup was designed which permits to remove layers from a strip substrate by electrochemical etching. Residual stresses in the directions that are longitudinal and transversal to rolling are determined by the curvature method based on the layer growing/removing techniques. As a reference, residual stresses were also determined by hole-drilling technique. Tensile and compressive residual stresses arose both in active and in passive layers and were considerably higher when determined by the hole-drilling technique.