Residual Stresses In Coatings Research Articles

A structured approach to the determination of residual stresses in an epoxy-amine coating and the influence of thermal ageing on the thermomechanical properties, residual stresses and the corresponding failure modes of coating

The purpose of this research was to develop a structured approach for the calculation of residual stresses in organic coatings through the experimental determination of thermomechanical properties of the epoxy-amine coating. The feasibility of this proposed method was validated by the presence of cracks on epoxy amine coating subjected to isothermal ageing at 180 °C for a period of 8 weeks, followed by thermal shock by water quenching at 0 °C, when the tensile strength of coating (8.00 MPa) was surpassed by the accumulated residual stress in the coating (9.66 MPa). The influence of thermal ageing on the thermomechanical properties, residual stresses and the corresponding failure modes were also evident. Significant variation of thermomechanical properties such as the increase in Tg from 77.60 °C to 120.50 °C, reduction of thermal expansion coefficient from 51.74×10−6°C−1 to 40.27×10−6°C−1, reduction of elastic modulus from 1600 MPa to 1400 MPa, and reduction of ultimate tensile strength from 27.00 MPa to 8.00 MPa after thermal ageing were observed. These variations have ultimately led to the increase of residual stresses in coatings that has resulted in the formation of cracks.

Residual Stresses in Coatings Formed by Electrospark Treatment

Residual Stresses in Coatings Formed by Electrospark Treatment

Residual Stresses in Coatings Formed by Electrospark Treatment

Residual Stresses in Coatings Formed by Electrospark Treatment

Estimation of Residual Stresses in Coatings of “Hard” Topocomposites by Repeated Microindentation

Estimation of Residual Stresses in Coatings of “Hard” Topocomposites by Repeated Microindentation

Study of the Evolution of the Residual Stresses in Thermal Barrier Coatings from Manufacturing to Its Operation Work

Residual stresses’ magnitude generated by deposition, quenching stress, thermal stress operation temperature, and infiltration in the thermal barrier coating (TBC) of gas turbines was determined. A thermal barrier coating was manufactured by the deposition of two layers, CoNiCrAlY and yttria-stabilized zirconia (YSZ), on an AISI 304 stainless steel substrate. The CoNiCrAlY was deposited by using an HVOF gun and the YSZ by an atmospheric plasma spray (APS). The TBCs were heat-treated at 1250 °C, with a CMAS (CaO, MgO, Al2O3, and SiO2) attack with a concentration of 10 mg/cm2 for 6 h in order to evaluate the evolution of the state of residual stresses in the coating at a high temperature. Residual stresses were determined by employing the modified layer removal method for duplex coatings (MLRMDC), ANSYS Version R19.2, and the equations proposed by Noda et al. In the YSZ, the total maximum residual stresses were 139 MPa in compression, and in the CoNiCrAlY, the maximum residual stress was 214 MPa in compression. The factor that has the largest effect on the magnitude of residual stresses was the infiltration of the CMAS in the YSZ.

Mechanical Properties of Arc Coatings Sprayed with Cored Wires with Different Charge Compositions

The mechanical properties (hardness, cohesion, and residual stresses) of arc coatings designed for operation under conditions of boundary friction and corrosive-abrasive wear are analyzed. The coatings were formed by arc spraying cored wires (CW) with different charge compositions (the content of carbon, aluminum, and boron in CW charge varied). It is shown that the hardness of the coatings increases with an increase in the carbon content in them up to 1 wt. %, and then decreased due to an increase in the content of residual austenite in their structure. The level of residual stresses of the first kind in such coatings increased by four times with an increase in the carbon content to 2 wt. %. The hardness of the coatings and the level of residual tensile stresses in them also increase with a decrease in the aluminum content in them. In this case, the cohesive strength of the coatings increased due to the implementation of aluminothermic reactions in the droplets of the CW melt during their flight and crystallization on the sprayed surfaces. However, then, with an increase in the aluminum content in the coatings of more than 2 wt. %, their cohesive strength decreased. The level of residual tensile stresses in coatings with a high content of retained austenite decreased after heat treatment (tempering) of the specimens. Sometimes, after tempering, these stresses even transformed into residual compressive stresses (in particular, under using CW C1.4Cr14Ni2). At the same time, the tempering of specimens with a predominance of ferrite in the coating structure increased the level of residual tensile stresses in them, which is due to the precipitation of finely dispersed carbides or borides. It has been shown that the addition of boron-containing components (ferrochromium-boron, chromium-boron) to the composition of the CW charge leads to a significant increase in the hardness of the coatings. Thus, an increase in the boron content in coatings from 0 to 4 wt. % leads to an increase in their hardness from 320 HV to 1060 HV. However, this is accompanied by an increase in tensile residual stresses in the coatings and a decrease in their cohesive strength.

Determining the Residual Stresses in High-Chromium Cast Iron Plasma Coatings

The paper presents the results of studies of the plasma spraying modes effect on the level of residual stresses in coatings. The analysis of experimental data has shown that the sign of residual stresses is not changed in the spraying process. The magnitude of the tensile stresses mainly depends on the temperature of samples heating, the biggest influence being that of plasma torch current arc. An increase in the current leads to an increase in the substrate temperature, which is explained by the increase in the thermal power of the plasma jet. An increase in the flow rate of the plasma-forming gas leads to a decrease in the temperature of the samples, since the heat content of the plasma decreases. An increase in the spraying distance has a similar effect, and its increase leads to a decrease in the substrate temperature. We obtained the functional dependence of the residual stress level on the plasma spraying modes.

Effects of sample bias on adhesion of magnetron sputtered Cr coatings on SiC

Swelling of SiC at 300 ∘C due to in-service neutron irradiation causes tensile residual stresses in coatings which are expected to adversely affect the performance of coated SiC composite fuel cladding for light water reactors. Matching the coating swelling with the substrate, a solution common for thermal expansion, is not practical in the case of neutron irradiation. Biasing samples during magnetron sputtering deposition induces compressive residual stress which may counteract this. In this study, chromium coatings were deposited on SiC by DC magnetron sputtering with no external heating at bias voltages of –50V, –75V, and –100V. The effects of the bias voltage on morphology, residual stress, microstrain, texture, and adhesion are shown. The low deposition temperature resulted in the coating microstructure evolution following an energetic particle bombardment dominated trend. At the two lower bias voltages knock-on implantation dominated increasing the residual stress and microstrain while at the highest bias voltage, thermal spike migration allowed for defect relaxation. When the knock-on induced compressive residual stress exceeded 0.8 GPa microcrack formation in the SiC substrate decreased coating adhesion. While no microcracks formed at the lowest bias voltage, insufficient atomic mobility during coating growth lead to voids forming in the coating. A balance is needed to form void-free coatings that have high compressive residual stress.

DETECTION OF RESIDUAL STRESSES IN COATINGS OBTAINED BY THE METHOD OF ARC METALLIZATION WITH A PULSATING SPRAYING FLOW

Purpose. The authors propose to develop a mathematical model for the calculated determination of residual stresses in arbitrary layer of a thermal gas coating based on the change magnitude in the base geometry (sample deflection) and the variation law of the layer thickness derivative, further regulation of these stresses by changing the technological parameters of spraying for each type of sprayed coating. Methodology. Based on known works on stress detection of in welded joints, the approach of determination of samples deflection after layer-by-layer spraying was developed. These deflection parameters are the basis for the developed mathematical model of influence on the stress state. The data on the study of the main types of residual (internal) stresses, as I type, distributed in the volume of the whole part (sample) with coating, and II type, localized in the volume of sprayed particles, are systematized. Findings. We presented investigations of the residual stresses arising in the applied layer, the magnitude and nature of the distribution of which depend on the type, base and sprayed materials, methods and parameters of spraying, the rigidity of the part, and other factors. The important role of evaluating residual stresses in a thermal gas coating by the calculation method is shown in connection with the complexity of the experimental determination of the kinetics of stress development in the coating-base composite. Originality. The authors of this work, on the basis of the first created mathematical model and software product Mathcad-Prime 6 2020, conducted a study of the level and principles of the formation of residual stresses in the coating during gas-thermal layer-by-layer spraying with various material, including the possibility of using a pulsating spraying air flow. Analytical studies have shown that the attention in the literature over the past five to seven years has been paid only to the study of residual stresses and deformations in welded joints, and only the growing interest in spraying technology opens up wide possibilities for studying the formation of stress fields in a thermal gas coating. Practical relevance. The results obtained in this paper confirm the formation of residual stresses in coatings and can be used as computational programs to solve design tasks, as well as for educational purposes during experts training in engineering fields.

Correlation between residual stresses and the tribological behaviour of Inconel 625 coatings

Residual stresses in thermal spray coatings are amongst the major limiting factors in achieving maximum performance of these coatings in both corrosive and high wear service environments. Moreover, due to the complexity of their origin and distribution in coatings there is a lot of variability in studies aimed at understanding their nature and influence on performance of thermal spray coatings. The aim of the research work was therefore to investigate the effect of residual stresses on the tribological behaviour of high velocity oxy-fuel sprayed Inconel 625 coatings. In order to achieve different stress states, coatings were deposited at different thicknesses of 250 μm, 300 μm, 400 μm and 500 μm. The sin2ψ method was then used to determine the evolved surface residual stresses in the coatings. Sliding wear tests were carried out at three loads of 70 N, 110 N and 150 N in order to study the influence of the residual stresses on the frictional and wear behaviour of the coatings under different loading conditions. The coefficient of friction was observed to decrease with increasing sliding load for all the Inconel 625 coatings of different thicknesses. A positive correlation was established between the residual stress state of the coatings and their wear volumes at the different loading conditions.

Study of Part Restoration Modes Using Electrocontact Welding with Gauze Filler Materials

This article proves the advantage of gauze compared to the wire, tape, and powder materials as a filler material for electro contact welding. The gauze as a tape material consisting of wires has the advantages of wire (high adhesive strength and high fatigue life) and the tape advantages (high producibility, ease of use). The paper presents the coating study methods and results using gauze welding and the effect of this coating on the adhesive strength depending on electro contact welding modes, material and gauze parameters, residual stresses in coatings, and coating wear-resistance. During electro contact welding in rational modes, the woven gauze adhesive strength is 41% higher than the steel tape. When analyzing residual stress as a relation of the effective stress to the material yield strength of the sample or coating, it was found that residual stresses have a smaller effect in the woven gauze coating compared to the tape made of steel 45. A stainless steel woven gauze coating and a steel tape coating made from steel 45 are equal in wear resistance. Thus, a metal gauze can be used as filler material during electro contact welding on the surface of worn parts instead of steel tape made from a similar grade of steel applied to the worn parts' surface.

Experimental and Numerical Investigation of Residual Stress in Coatings on Steel

Abstract In the present work, an alumina–titania (13 %) coating has been deposited by the air plasma spray process on a mild steel substrate by preheating the substrate to different temperatures. Coating thickness was measured by a scanning electron microscope, the hardness of coatings was measured, and morphology was also checked. The crack compliance technique has been used to determine the residual stress, as it is a very simple method, and also, it is compatible with conventional machining equipment and wire electric discharge machining equipment. Specimens were cut by the diamond cutter up to certain depth in microns, and the strain relieved was recorded. For finding out the residual stress, these recorded values of strain have been used by doing a finite element analysis (FEA) using the ANSYS 15.0 (Ansys, Inc., Canonsburg, PA) software. For validation of the model, uniaxial tension was applied on a sample by using the INSTRON universal testing machine (Instron Inc., Norwood, MA), and strain values at both the coating side and the substrate side were recorded and matched with the model under the same value of the load. After verifying the model, an equation has been developed using the Minitab software (Minitab Inc, Bengaluru, India), and the strains previously recorded were used as an input to the equation obtained, and the value of residual stress was calculated. The maximum value of residual stress was found at the coating–substrate interface, and the values of residual stress for sample preheated at 250°C, 200°C, and 150°C were found to be compressive, with the magnitude of −176.28 MPa, −243.54 MPa, and −255.42 MPa, respectively.

Evaluation of Residual Stresses and Their Influence on Cavitation Erosion Resistance of High Kinetic HVOF and HVAF-Sprayed WC-CoCr Coatings

Thermal spray processes have been developing toward lower particle temperature and higher velocity. Latest generation high-velocity oxygen-fuel (HVOF) and high-velocity air-fuel (HVAF) can produce very dense coating structures due to the higher kinetic energy typical for these thermal spray processes. Thermally sprayed coatings usually contain residual stresses, which are formed by a superposition of thermal mismatch, quenching and, in case of high kinetic energy technologies, peening stresses. These stresses may have a significant role on the mechanical response and fatigue behavior of the coating. Understanding these effects is mandatory for damage tolerant coating design and wear performance. For instance, wear-resistant WC-CoCr coatings having high compressive stresses show improved cavitation erosion performance. In this study, comparison of residual stresses in coatings sprayed by various thermal spray systems HVOF (Thermico CJS and Oerlikon Metco DJ Hybrid) and HVAF (Kermetico AcuKote) was made. Residual stresses were determined through thickness by utilizing Tsui and Clyne analytical model. The real temperature and deposition stress data were collected in the coating process by in situ technique. That data were used for the model to represent realistic residual stress state of the coating. The cavitation erosion and abrasion wear resistance of the coatings were tested, and relationships between residual stresses and wear resistance were discussed.

Simulation research on the thermal-mechanical coupling of YSZ thermal protective coatings prepared by laser-plasma composite heat source on the surface of high-intensity diesel engine cylinder head

To improve the reliability of the coating, a laser-plasma composite heat source was used to prepare the YSZ coating. Based on the thermo-elastoplastic finite element theory and using ANSYS simulation software, a numerical model of laser-plasma composite heat source for YSZ coating was established. The model took into account the thermophysical performance parameters of the material at different temperatures and the latent heat of the phase transition of the material. The paper focused on the value and distribution of the temperature and the residual stress of coatings when the powder deposition temperature was 300 °C, 500 °C, 700 °C, and 900 °C. The results showed that with the increase of powder deposition temperature, the maximum temperature of the component increased. The micro-metallurgical morphology existed at the interface between the coating and the substrate prepared by the laser-plasma composite heat source. With the increase of powder deposition temperature, the depth and width of the molten pool of the substrate tended to increase further under the combined effects of the thermal conductivity of the component itself and the convective heat transfer between the component and the external environment. With the increase of powder deposition temperature, both the lateral maximum residual tensile stress and the lateral maximum residual compressive stress of the component increased. With the increase of powder deposition temperature, the longitudinal maximum residual compressive stress of the component increased and the longitudinal maximum residual tensile stress decreased.

Mathematical Modeling on the Residual Stresses in Coatings Due to Heat Treatments

Coatings are implemented on engineering metals and alloys to augment the surface properties such as hardness as well as resistance to wear and corrosion. Heat treatments of coated metals/alloys are performed to aid in the progress of the bonding of the coatings to the substrate. During the air cooling process, the difference in the compositions of the coating and the substrate materials causes them to cool at different rates, which leads to straining in them. The paper presents the research on the mathematical investigation to evaluate the residual stresses in coatings caused due to heat treatments and subsequent air cooling. The mathematical modelling is executed to formulate the equations to represent the residual stresses retained in the coatings due to the heat treatments and subsequent air cooling. Air cooling undergoes two stages namely the initial quenching phase and the final cooling phase. During the quenching phase, the strain was expressed by considering the elastic, plastic and thermal strain components. Poisson’s ratio, deviatoric stress differential of the modulus of plasticity, coefficient of thermal expansion and change in temperature are used to express the elastic, plastic and thermal strain components. During the final cooling phase, the strain was expressed by considering only the elastic and thermal stain components, as the plastic staining the coating material generally does not occur during the final cooling phase and occurs only during the initial quenching phase. From the strain components, the residual stresses for the coatings in the x, y and z axis were formulated. Thus, the total residual stress is the sum total of stresses caused during the initial quenching phase and the final cooling phase.

Influence of bias voltage on structure and mechanical properties of TiCrN-Mo2N-Ni coatings

In this work, the influence of bias voltage on the structure, composition and physical properties of TiCrN-Mo2N-Ni arc Physical Vapor Deposition (arc-PVD) coatings were studied. Multilayer structure formed at all applied bias voltage due to planetary rotation of substrates. Thickness of sublayers range from 1 to 32 nm and defined by the plasma flow intensity from evaporators. Monte-Carlo calculation was used to study structure of prepared coatings. According to calculation and analysis of TEM images, sublayers composed by nitrides mixture. All coating characterized by high hardness, which correlated with residual stress of coatings.

Study on Local Residual Stress in a Nanocrystalline Cr2O3 Coating by Micro-Raman Spectroscopy

Residual stress in coatings often affects the service performance of coatings, and the residual stresses in some local areas even lead to premature failure of coatings. In this work, we characterized the residual stress of local micro-areas of a nanocrystalline Cr2O3 coating deposited on a Si wafer through micro-Raman spectroscopy, including the depositional edge zone where the electrode was placed, the micro-area containing Cr2O3 macroparticles, and other micro-areas vulnerable to cracks. To accurately measure the thickness of the coating, we combined optical interferometry and direct measurement by a profilometer. The results indicate the existence of in-plane tensile residual stress on the Cr2O3 coating. In thick coatings, the residual stress is independent of the coating thickness and is stable between 0.55 GPa and 0.75 GPa. As the coating thickness is less than 0.8 μm, the residual stress is directly related to the coating thickness. This in-plane tensile stress is considered as the origin of the observed microcrack, which can partially release the stress.

Effect of heat transfer on residual stresses in thermal spray coatings

Herein, heat transfer from the coating to the substrate during the thermal spraying process is simplified as one-dimensional heat conduction and a formula to express the temperature distribution in the substrate is provided. To achieve this, the spray process was divided into two stages, namely deposition (coating sprayed onto the substrate) and post-deposition (cooling of coating and substrate to atmospheric temperature). The coating was achieved through a layer-by-layer deposition method. Residual stresses in the system (including both the coating and substrate) following deposition of each layer were calculated, as well as those induced by post-deposition. Finally, the proposed formulae were implemented in a real-case example to illustrate the effect of heat transfer with regards to torch velocity on residual stresses. The simulative results were shown to have a better agreement with experimental results at low rather than at high torch velocities. The residual stresses in the coating surface decreased with the increase in heat transfer time. When the heat transfer time exceeded a certain value, a sharp decline in residual stresses was observed.

Effect of high-voltage pulse bias on the stress and morphology of CA-PVD TiN coatings

ABSTRACTWe investigated the role of high-voltage pulse bias (HVPB) on the structure, morphology and residual stress of TiN coatings produced with cathodic arc physical vapour deposition and compared them with the ones produced with DC bias. Annealing heat treatment was also performed for surveying stress-relieving behaviour within the coatings. The preferred orientation of the coatings changed from (111) to (220) by the application of HVPB. Coatings produced with DC bias exhibited Zone T structure, while the growth morphologies of the coatings produced with HVPB were very similar to the structures in the beginning of Zone II. The presence of Ar in the deposition environment increased the residual stress of all coatings. Intra-grain stresses of the coatings produced with DC bias were almost totally annihilated by annealing. However, for coatings produced with HVPB, stress relief magnitudes were very low, indicating that intra-grain defects could not be totally annihilated.

Microstructural Characteristics and Residual Stresses in Arc-Sprayed Cermet Coatings Using Different Carbide Grain Size Fractions

Different studies have emphasized the technological relevance of residual stresses in engineered surfaces, such as thermally sprayed coatings, and their effect on the fracture and fatigue behavior. In arc-sprayed coatings, the microstructural characteristics and resulting residual stresses are determined primarily by the inherent process characteristics and feedstock material. With the scope of this work, a study on the residual stress field in coatings formed by an arc spraying process for different electric parameter settings has been carried out using different wire configurations. Thus, iron-based cored wires with different grain-sized tungsten carbides as filler material were used as feedstock. The coatings are mainly composed of eutectic carbides, and eta carbides such as M6C, M12C, or M23C and some iron-rich oxide phases, as well as characterized by an inhomogeneous, lamellar microstructure. The results demonstrated that the magnitude of the residual stresses in the coating depends on the carbide grain size fraction used as filling for cored wires. A smaller carbide grain size leads to a more pronounced dissolution of eutectic carbides, resulting in the formation of eta carbides, which in turn is accompanied by decreased tensile residual stresses across the coating. With respect to the spray parameter settings, reduced tensile residual stresses are observed when an increased voltage is applied, which can be attributed to phase evolution phenomena during spraying and thermal effects on the substrate-coating system.