Analysis of Thermal History and Residual Stress in Cold-Sprayed Coatings (original) (raw)
Related papers
Experimental and numerical study of residual stress evolutionin cold spray coating
Residual stresses are among the most important factors affecting the properties and service lifetime of materials and components. In the cold spray coating process there are two contradictory factors that influence the final residual stress state of the coated material; the impact of the high velocity micron-size particles induces compressive residual stresses, whereas the gas temperature can have an opposing annealing effect on the induced stresses. These two simultaneous phenomena can in turn change the residual stress profile, thus complicate the assessment of the final residual stress state.In this paper the residual stress evolution during cold spray coating process has been studied through experimental measurements and numerical simulations performed on several series of samples coated using different spray process parameters. A detailed finite element (FE) analysis of the process has been developed to calculate the stresses induced through impacts and then the annealing effect has been taken into account through an analytical model. The results of the experiments and numerical–analytical approach confirm the considerable effect of annealing on the eventual stress distribution in the coated samples.
Thermal Spray 2021: Proceedings from the International Thermal Spray Conference, 2021
The understanding of residual stress is of critical importance in the cold spray and thermal spray processes. It has a direct effect on the integrity of the coating related to the adhesion strength, fatigue life, and can lead to undesired effects such as the delamination of the coating. In cold spray, several investigations have evaluated the impact of the residual stress on the coatings, and it is generally accepted that cold spray coatings follow a similar profile to those obtained in the shot peening process. Although the measurement of residual stresses gives fundamental insight into the process, the estimation of such stresses considering the deposition of each layer by numerical methods has not been extensively studied. This work proposes a method for analyzing the evolution of residual stress on a cold spray coating, both on the coating and the substrate, as a function of the deposited layers, using Finite Element Analysis (FEA). The evolution of the residual stress profile w...
Numerical modelling of particle impact and residual stresses in cold sprayed coatings: A review
Surface and Coatings Technology, 2021
Cold spray technology provides protective coatings, additive manufacturing and repair to a wide array of industrial sectors. Alternative tags for cold spray include, kinetic metallisation, kinetic fusion, hypersonic spray, gas dynamic cold spray, cold spray printing, and cold spray additive manufacturing. These processes employ the same physics principles of accelerating micrometre-sized particles to supersonic velocities that impact and adhere onto a suitably prepared substrate. Numerical modelling has been used extensively to study particle impact modelling. The prediction of critical velocity, deformation mechanism and, more recently, residual stresses have been areas of interest that have been evaluated by numerical methods such as Lagrangian, Eulerian, Smoothed Particle Hydrodynamics, Coupled Eulerian-Lagrangian, and Molecular Dynamics. The crucial findings of these models are summarised, and their comparative outcomes assessed with a critical analysis of their merits and weaknesses. The process parameters applied in the simulations such as particle diameter, impact velocity, pre-heat temperature and material chemistry is compiled. The experimental techniques used for residual stress measurements; such as X-ray diffraction, neutron diffraction, material removal, curvature measurement and deformation techniques, are concisely reviewed from the context of being applied to cold spray deposits.
Modeling Residual Stress Development in Thermal Spray Coatings: Current Status and Way Forward
Journal of Thermal Spray Technology, 2017
An overview of analytical and numerical methods for prediction of residual stresses in thermal spray coatings is presented. The various sources and mechanisms underlying residual stress development in thermal spray coatings are discussed, then the various difficulties associated with experimental residual stress measurement in thermal spray coatings are highlighted. The various analytical and numerical models used for prediction of residual stresses in thermal spray coatings are thoroughly discussed. While analytical models for prediction of postdeposition thermal mismatch stresses are fully developed, analytical quenching and peening stress models still require extensive development. Various schemes for prediction of residual stresses using the finite element method are identified. The results of the various numerical and analytical models are critically analyzed, and their accuracy and validity, when compared with experiments, are discussed. Issues regarding the accuracy and applicability of the models for predicting residual stresses in thermal spray coatings are highlighted, and several suggestions for future development of the models are given.
In situ measurement of residual stresses and elastic moduli in thermal sprayed coatings
Acta Materialia, 2003
Mechanical properties, such as residual stress and Young's modulus, play a critical role in the synthesis and performance of thermally sprayed coatings. Thus, it is important to understand their evolution, the influence of processing parameters, and to be able to determine them accurately. The first part of this two-part paper presents a novel in situ curvature method for determination of stresses and Young's modulus of plasma sprayed coatings. The principle of the method is explained, details of the instrument are provided and the analytical procedure is described. The capabilities of the method are discussed in detail, namely the ability to observe the stress evolution during the entire spraying process, to separate the quenching and thermal stress contributions to final residual stress and to determine the Young's modulus of the coating. Brief examples of application are also included, and the potential for use of this method for process control of coating quality is addressed. In the second part, a case study for plasma sprayed molybdenum will be presented, focusing on the influence of the key processing parameters.
Surface and Coatings Technology, 2006
Coating and layer composite manufacturing most commonly involves high temperature gradients and intensive heat transfer between the different composite materials. This can be noticed not only for thermal spraying, but also for other coating techniques. The combination of temperature gradients and materials with different thermophysical properties leads to the formation of thermal stresses in the composite, which are superimposed by stress generating effects during coating solidification, phase transformation or recrystallization. The final state of residual stresses affects the structural and functional properties of the coating as well as the component reliability during operation. Therefore, residual stress analysis is an important tool for the optimization of coatings and layer composite manufacturing processes in order to ensure stability of the processes, adhesion and compatibility of the coating, and finally, the reliability of the components in various technical systems.
Effect of Shot Peening on Residual Stresses and Surface Work-Hardening in Cold Sprayed Coatings
Key Engineering Materials, 2009
Coating deposition processes such as cold spraying are commonly employed to increase wear and fatigue resistance and consequently to enhance longevity of engineering components. Such processes typically introduce residual stresses into the coated surface, which in turn affect efficiency of coatings and play an important role in coating durability. Present study describes alteration of residual stress state and surface work-hardening of two types of aluminum coatings that are cold sprayed onto aluminum substrate, and subsequently treated by air blast shot peening (ABSP). Residual stress measurements have been made by means of X-ray diffractometer (XRD) on coated samples both before and after shot peening process. The results indicate that that the effect of shot peening is more marked in terms of surface work-hardening than of residual stresses and allow some consideration to correctly orient the choice of peening parameters in practical application.
Residual stresses and adhesion of thermal spray coatings
Surface Engineering, 2005
Residual stresses generated in coatings during thermal spraying could have very different inside intensity and distribution, depending on the materials and processing conditions. As it is recognised that residual stresses play a major role in the adhesion of coatings, it is necessary to evaluate precisely their influence. It is not possible to conduct these measurements directly, and no indication on how the stresses should be taken into account has been reported in the literature. Moreover, depending on the test used to evaluate adhesion, different volumes of the coating can participate in the delamination process. In order to take into account these observations, it is proposed to define two stress parameters related either to the stresses in the coating or to the stresses at the interfacial zone. In these conditions, it is possible to explain the variation in adhesion as a function of the coating thickness, i.e. to explain the maximum value obtained for the bonding strength deduced from tensile tests and the monotonic increase in adhesion toughness deduced from interfacial indentation tests.
Influence of Vacuum Heat Treatment on the Residual Stress of Thermal Spray Cermet Coatings
World Congress on Engineering, 2007
The aim of this investigation was to ascertain the changes in residual stress profile after the post-treatment of functionally graded thermal spray WC-NiCrBSi coatings, and relate these changes to the microstructural transformations. Through thickness residual stress measurements were performed using the neutron diffraction and x-ray diffraction techniques. Functionally graded HVOF (JP5000) WC-NiCrBSi coatings were thermally sprayed on AISI 440C steel substrate discs. These coatings were then heat-treated in an inert atmosphere at 1200 o C for one hour. Microstructural investigations using SEM, XRD, and light microscopy were used to identify the changes after the heat-treatment. Microhardness and indentation modulus values were also investigated to analyse the changes in the mechanical properties after the heat-treatment. Results of this investigation indicated that the residual stress gradient within the coating material decreases after the heat-treatment, and the stress field in the substrate, near the coating substrate interface, changes from tensile to compressive. Residual stress measurements via x-ray diffraction provided average compressive values which were similar to those evaluated via the neutron diffraction technique, however the definition of stress gradient as a function of coating thickness was much better resolved via the neutron diffraction technique. The changes in the stress gradient after the heat-treatment were related to the microstructural changes which resulted in the formation of diffusion zones at the coating substrate interface, and also at the interface of functionally graded coating, improvement in coating elasticity due to the changes in the bonding mechanism from mechanical interlock to metallurgical bonding, and the formation of secondary phases within the coating microstructure.
Number of Passes and Thickness Effect on Mechanical Characteristics of Cold Spray Coating
Procedia Engineering, 2014
Nowadays, with severe competitive business environment, limited material sources and high cost of manufacturing, the importance of maintenance and repair is self-evident. In this field, cold spray technology is gaining more and more attention especially in light alloy components. One of the potential applications of cold spray coating is dimensional recovery of damaged structural parts. In most cases, thick coatings are necessary to fill the damages such as cavities, worn or corroded parts. Thick coatings can be deposited in a single or multiple passes giving different thermal input and stress distribution to the substrate and coating itself. The thermal input, the amount and type of residual stress (compressive or tensile) confer appreciable or depreciable characteristics to the coating mechanical properties. In this study, single and multi-pass deposition of a 0.5 mm thick Al 6082 coating on the same substrate is studied to explore the number of passes effect on mechanical characteristics. In addition, one pass deposition of 0.65 and 0.8 mm thick coating is investigated to examine the thickness effect. Micro-structural observation, micro-hardness measurements and X-Ray diffraction (XRD) measurement of residual stress were performed on all groups. Adhesion test and tubular coating tensile test were also carried out to characterize the coating in different cases. Observation of fractured surface was used to investigate the failure mechanism of the cold-sprayed coating. A critical discussion on the effects of pass number and thickness on mechanical properties of coated specimens is presented.