Effect of Shot Peening on Residual Stresses and Surface Work-Hardening in Cold Sprayed Coatings (original) (raw)
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Analysis of Thermal History and Residual Stress in Cold-Sprayed Coatings
Journal of Thermal Spray Technology, 2014
Residual stress in coatings has significant effect on their performance. In cold-sprayed coatings, in which particles impact the substrate at high velocity in solid state, in-plane residual stresses are usually conceived to be compressive. In this research, analysis of residual stresses in cold-sprayed deposits is performed by analytical and numerical modeling. The influence of various parameters such as the dimensions and elastic properties of the coating and the substrate on the residual stress are analyzed. In addition, the amount of heat input as a key parameter in the build-up of the residual stress is examined. It has been found that the heat input and the associated thermal history have a major influence on the final distortion and the residual stress, to an extent that the in-plane stress can in some cases change from compressive to tensile. Based on these results, a simple model is put forward for the prediction of the final state of the stress and distortion in cold-sprayed flat components.
Materials Science and Engineering: A, 2004
Thermal spray offers a variety of subsets of processing approaches to produce coatings. The various processes are classified based on the thermal spray source (from low velocity combustion spray to high temperature plasma jets) and method of material injection (in the form of powder, wire or rod). However, it is this intrinsic versatility which sets-up variations in characteristics of the applied coatings. Properties of thermally sprayed coatings, including process induced residual stress, are controlled by various parameters of the spraying process. This study examines three thermal spraying techniques with significantly different particle temperatures and velocities. They are air plasma spraying (APS), twin wire-arc spraying (TWA) and high velocity oxy-fuel (HVOF) spraying. For comparison purposes the recently developed cold spray processed materials were included in the study. For each method, in-flight particle diagnostics was performed; Ni-5 wt.%Al splats and deposits were fabricated and analyzed. Porosity, elastic modulus and thermal conductivity of the deposits were evaluated and correlated to the process variables. Using indentation at different loads and analysis of the indented region, stress-strain relationships for these coatings were obtained. Surprising differences in the properties were observed and were explained based on the fundamental variations in microstructure development. Through-thickness residual stress profiles in Ni-5 wt.%Al coatings on steel substrates were determined non-destructively by neutron diffraction. The stresses range from highly tensile in the APS coating to compressive in the HVOF coating. Various stress generation mechanisms-splat quenching, peening and thermal mismatch-are discussed with respect to process parameters and material properties.
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...
Coatings
Cold spray is a promising approach to repair all damages and defects in aluminum (Al) constituent elements. The study aims to investigate the mechanical and tribological properties of Al coatings deposited using high-pressure cold-spray (HPCS) and low-pressure cold-spray (LPCS) techniques. Al powder was sprayed on a cold-rolled plate of aluminum 1100, which was used as the substrate. The results showed that the micro-hardness of the LPCS Al coating reached up to 196.6 HV before the wear test compared to that of HPCS (174.3 HV). Moreover, more low friction coefficients obtained by LPCS (0.798) than HPCS (0.807) indicated good tribological properties with a high amount of oxide composition. Meanwhile, the wear studies reveal that the specific wear rate of the Al coating of LPCS (0.008) was lower than the HPCS (0.009) as the load increased from 3 N to 5 N, thus providing excellent wear resistance. Therefore, the results exhibited greater mechanical and tribological characteristics for ...
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.
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.
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.
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.
Surface Engineering, 2001
In this work, the influence of the thermal spraying in traction in the APS, V PS, and HVOF coatings: the residual stress level in the HV OF and APS coatings is processes, atmospheric plasma spraying (APS), high less important than that in the VPS coating. T he velocity oxygen fuel (HV OF), and vacuum plasma microstructure observations show that the VPS copper spraying (V PS), on the microstructure and properties coating has a recrystallised structure whereas the APS of copper coatings is discussed. T he diVerences in and HV OF copper coatings have a splat type structure. microstructure, microhardness, and residual stress for As a consequence, the VPS copper coating has a high each type of coating are shown. T he X-ray diVraction Young's modulus, an important mechanical resistance, (XRD) method is used to evaluate the mechanical and a high elongation as compared with the other anisotropical characteristics of the materials and the copper coatings. SE/S185 residual stress distribution. T he particularity of this study is that the thickness of the coating is of the Dr Gassot and Dr Junquera are at the Institut de millimetre scale; the massive coating specimens without Physique Nucléaire d'Orsay,
It has been observed that the method of substrate surface preparation can have a profound effect on the adhesion strength of cold-sprayed metallic coatings. In this investigation, pure aluminum powder was sprayed onto aluminum alloy substrates using cold spray. The substrates used in this work had undergone a variety of surface preparations to impart varying degrees of surface roughness. The pulsed waterjet technique was used to increase the substrates surface roughness beyond what can be achieved using traditional grit blasting procedures. Surfaces prepared using pulsed waterjet resulted in substantial increases in the pure aluminum coating adhesion strength. This increase may be the result of increased mechanical anchoring sites available as well as their favorable geometries. It is hypothesized that compressive residual stress may also contribute to increased adhesion strength.