Value Of Residual Compressive Stress Research Articles

Development of low-stress SiC coating on single crystal Si using low elastic modulus SiOC amorphous buffer layer

In this study, we successfully prepared low-stress SiC coatings on single-crystal Si substrates using the organometallic chemical vapor deposition (MOCVD) technique. For this purpose, the SiOC buffer layer (with low hardness and low elastic modulus) was initially deposited on the substrate and then the SiC coating was directly deposited on the buffer layer. A series of both, the buffer layer and the SiC coating, were separately deposited at various process conditions to pinpoint their optimized combination. Results revealed that the residual compressive stress value for the optimized SiC composite coating (containing low elastic modulus SiOC buffer layer) was 87.9% lower than that of the single SiC layer. The findings of this study are of great significance for the production and integration of the SiOC buffer layer and the SiC coating which not only improves the production efficiency but also reduces the production costs low-cost power devices.

Mechanical and electrical properties of sodium potassium niobate ceramic coating by plasma spraying

Potassium sodium niobate ceramics are environmentally friendly piezoelectric ceramics with excellent electrical properties. It is the most promising green piezoelectric ceramic for current applications. Currently, ceramics are needed in the form of thin films or coatings for brakes, sensors, etc. Most of the current ceramic films are prepared by physical vapor deposition and chemical vapor deposition. However, the ceramic layers prepared by the above methods are thin. The thickness of the ceramic layer has a large influence on its mechanical and electrical properties. The coatings prepared by thermal spraying are thicker, but there is no in-depth study about the relationship between the coating thickness and the mechanical and electrical properties of the coating. In this article, four different thicknesses of coatings were prepared by plasma spraying technology, and the relationship between the mechanical and electrical properties of the coatings and the thickness was studied and discussed. The results show that the coating microhardness and residual compressive stress values reach the maximum and the dielectric and ferroelectric properties are optimal when the coating thickness reaches 300 μm. The study of the connection between coating thickness and coating mechanical and electrical properties provides a theoretical study for the application of the coating in practice.

Optimizing Parameters with FEM Model for 20CrMnTi Laser Shocking

As a new surface treatment technology, laser shock peening (LSP) is a multi-point overlay process of single-point laser shock. In this study, the finite element method (FEM) was used to build a model of single-point laser shock, and the model was verified by experiments. The difference in residual stresses between the experimental and simulated results was less than 20%. Then, the effects of the stress field and deformation of 20CrMnTi with different laser shock parameters were simulated and analyzed. According to the mechanical response of 20CrMnTi to different laser shock parameters, the optimal shocking process parameters for single-point shocking via LSP were determined to be a shock energy of 5 J, a laser pulse width of 20 ns, and an impact number of 5. Lastly, a simulation of multi-point laser shock was performed with the optimal parameters, and the residual compressive stress values of multi-point impacts are close to those of single-point impacts under the same process conditions.

Analytical model of residual stress in ultrasonic rolling of 7075 aluminum alloy

Ultrasonic rolling produces large values of residual compressive stress (RCS) in the surface layer of metal part, thereby significantly enhancing the fatigue resistance of the part. Ultrasonic rolling is a complex elastic-plastic deformation process, and it is difficult to accurately predict the residual stress produced by ultrasonic rolling. 7075 aluminum alloy was processed in this work. The elastic-plastic deformation caused by “loading-unloading” during ultrasonic rolling was analyzed based on Hertzian theory and elastic-plastic deformation theory. The residual stress model of ultrasonic rolling was developed by considering the effects of initial surface residual stress and plastic indentation depth. Finally, the model was verified by experiments. The numerical analysis results show that the surface RCS, the value and depth of the maximum RCS and thickness of the RCS layer increase to different degrees with the increment of the static load, the amplitude and the roller radius. The trend of the experimentally obtained surface RCS value with static load is consistent with that of the numerical calculations. The surface RCS increase with the increasing of the static load. The maximum error between the calculated RCS and the experimental result is no more than 10 %. The proposed residual stress model in ultrasonic rolling is relatively reliable.

Effects of grinding treatment on surface properties and deformation microstructure in alloy 304L

Different types of sandpapers were used to grind surface of 304L alloy, and the effects of grinding treatment on surface properties and deformation microstructure were studied. Three dimensional profilometer, Vickers hardness tester, X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB), and transmission electron microscopy (TEM) were used to characterize the microstructure and mechanical properties. The results showed that with the increase of grinding particle size the surface roughness and hardness increased, while the absolute value of residual compressive stress decreased, however the grinding particle size had no effect on the average tension strength because the groove did not lead to the effect of notch stress concentration. After grinded by coarse sandpaper (No. 60), the surface metal deformed in the way of martensite shear from γ-austenite to α′-martensite, which conformed to K-S model, and surface nano-crystal layers with a thickness of about 2.3 μm, 1.5 μm and 0.6 μm were found at the groove peak, slope and valley, respectively. By comparison, after grinded by fine sandpaper (No. 2000), the nano-crystallization did not occur, and a high-density dislocation layer with a thickness of more than 1 μm was observed at the groove peak, slope and valley. • Hardness increase and compressive stress decrease with the increase of roughness. • Roughness had no effect on tension strength and notch stress concentration. • Surface metal deforms in the way of γto nano-α′ after grinded by No. 60 sandpaper. • Thickness of nano-α′ layer at groove peak, slope and valley decreases gradually. • Surface metal deforms as dislocation slip after grinded by No. 2000 sandpaper.

Simulation and experimental study on surface residual stress of ultra-precision turned 2024 aluminum alloy

In order to reveal the influence of cutting parameters on the surface residual stress of 2024 aluminum alloy in ultra-precision cutting, the thermal coupling simulation of 2024 aluminum alloy ultra-precision cutting process was carried out based on ABAQUS software, and it was verified by the residual stress test of ultra-precision machined samples. The results show that the dominant factor of the machining residual stress of 2024 aluminum alloy ultra-precision with single crystal diamond tool is the plastic deformation caused by cutting force. With the normal ultra-precision machining parameters, the residual stress of the machined surface of 2024 aluminum alloy is mainly compressive stress. With the increase in distance to the machined surface, the residual compressive stress value decreases and gradually transforms into tensile stress, and the total residual stress depth is less than 8 μm. With the increase in cutting depth (0.01–0.03 mm), the reduction of cutting speed (150–50 m/min) and the increase of feed (0.01–0.024 mm/r), there is an increasing trend of the residual stress on the machined surface of 2024 aluminum alloy workpiece, and the influences of feed rate and cutting depth on residual stress are slightly greater than that of cutting speed.

Research on Mechanical Properties of 210Cr12 Shaft Surface Processed with Rolling

The rolling process is one of the most effective ways for strengthening a part’s surface. As the press force exerted on specimen in rolling process, material in the surface layer will deform plastically if the press force is sufficient. That might result in grain refinement, dislocation configuration change, or phase change in specimen surface layer material. Consequently, the surface material mechanical properties can be changed. The effects of rolling parameters on surface residual stress, micro-hardness, and surface roughness for a 210Cr12 shaft have been investigated. After the rolling process, the surface residual stress of the specimen changes from tensile stress to compressive stress, and a stable residual compressive stress layer is formed. The maximum absolute value of compressive stress can be up to 216MPa. With the increase of the value of contact stress exerted on shaft surface and the number of rolling cycles, the absolute value of residual compressive stress increases firstly and then becomes stable. With the increase of depth from shaft surface to interior, the absolute value of residual compressive stress increases initially, then decreases and disappears finally. The maximum absolute value of residual compressive stress exists at the position beneath specimen surface about 0.025mm. The depth of residual stress layer is about 0.2 mm. Research results indicate that shaft surface microhardness can be improved within small range, surface roughness can be reduced up to 67%.

A surface integrity model of TC17 titanium alloy by ultrasonic impact treatment

Ultrasonic impact treatment (UIT) is a mechanical surface treatment. In this study, a surface integrity empirical model of TC17 titanium alloy by UIT was established to study the processing effect of UIT. A surface roughness index function prediction model was established. The relationship between microhardness, residual stress, and depth h was characterized by an exponential function and a decaying cosine function, respectively, and the relationship between the control factor and the process factor was established. The parameters such as feed rate, spindle speed, extrusion depth, and number of impact per unit area were analyzed to evaluate the result of UIT. The minimum roughness after ultrasonic impact treatment is 0.3 μm, and when the feed rate is 0.04 mm, the spindle speed is 50 r/min, the extrusion depth is 0.01 mm, and the number of impacts per unit is about 10,000 times; the microhardness layer is about 120 μm; the residual compressive stress layer is about 200 μm, the microhardness value is as high as 670 HV; and the maximum residual compressive stress value is − 1250 MPa.

Prediction of residual stress in the process of turning high strength alloy steel by innovative coated carbide microgroove tools

Residual stress (RS) of machined surface is one of essential factors affecting the service performance of mechanical structures and parts. By a combination of cutting experiment, theoretical analysis, and finite element analysis, this paper focuses on the radial distribution of RS of machined surfaces of a coated carbide microgroove turning tool (CCMTT), firstly, in the turning of the high strength alloy steel. The effect of cutting parameters on the radial distribution of RS of machined surfaces produced by the CCMTT is further researched. Finally, the prediction model of RS produced by the CCMTT is established and verified. Research results show that the cutting experiments and FE simulation both have the same variation tendency of RS and are validated well each other. The microgroove on the rake face of the CCMT is beneficial to increase the thickness and the maximum value of residual compressive stress of surface material. The coefficient of multiple correlation of the forecasting model of surface residual stress (SRS) machined by the CCMTT reaches 97.4%, which illustrates that the model has relatively high reliability.

Numerical research of influence of residual stress on interface crack propagation

The crack propagation was simulated by a generalized potential-based mixed-mode (PPR) cohesive interface model. Based on the principle of equivalence of thermal and mechanics, the effects of residual stress on interface crack propagation was researched by finite element model. The results demonstrate that residual compressive stress is more likely to cause material interface crack propagation. The material interface is more likely to fail when there is residual compressive stress in the material. The residual compressive stress is more likely to cause the interface crack propagation when the crack propagation length caused by certain residual compressive stress value is seen an important influence parameter.

On the Origin of Peaks of Differential Magnetic Permeability in Low-Carbon Steels after Plastic Deformation

The physical origin of peaks in the field dependence of differential magnetic permeability of low-carbon steels after their plastic tensile deformation have been theoretically studied; they are caused by the irreversible displacements of the 90° domain walls. The angular difference between the [100] axes of the two neighboring grains with the large-angle boundaries has been determined; it corresponds to the peaks of differential permeability. It also controls the value of residual compressive stress. The results obtained are in perfect agreement with the corresponding experimental data.

Effect of Ultrasonic Irradiation Conditions on Metal Surface during Multifunction Cavitation

Processing using multifunction cavitation (MFC) has recently enabled functional characteristics to be imparted to various materials. It is possible to process a material surface in the same manner as with conventional water jet (WJ) peening; however, the cavitation bubble temperature is different. To further improve this MFC technology, we examine the surface re-forming of low alloy steel (JIS-SCM435) using MFC with various modes of ultrasonic waves. The ultrasonic equipment used for MFC processing includes dual, single, pulse and frequency modulation (FM) ultrasonic modes. Improvement of the residual stress and corrosion resistance was confirmed for all modes. The dual mode showed the maximum values of residual compressive stress and surface potential. The sound pressure at the machining spot was the highest with dual mode, and the temperature in the bubble generated by the WJ nozzle was highest and the amount of dissolved oxygen was lowest. Improvement of the residual stress and corrosion resistance was promoted because the temperature and pressure in the bubble interior during processing was higher than in the other modes.

Equation Chapter 1 Section 1 The Numerical Research of Influence of Residual Stress on Interface Damage

The crack growth was simulated by mixed-mode cohesive interface model. Based on the principle of equivalence of thermal and mechanics, the effects of residual stress on crack growth and interface damage evolution are researched by finite element model. The results demonstrate that residual compressive stress is more likely to cause material interface crack growth and damage. The material interface is more likely to fail when there is residual compressive stress in the material. The residual compressive stress is more likely to cause the interface crack growth when the crack growth length caused by certain residual compressive stress value is seen an important influence parameter.

Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels.

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plate thickness of bainitic ferrite, hardness, and residual compressive stress value of the contact surfaces of the two steels under roughly similar conditions. The excellent RCF performance of the carburized nanostructured bainitic steel is mainly attributed to the following reasons: finer carbide dispersion distribution in the top surface, the higher residual compressive stress values in the carburized layer, the deeper residual compressive stress layer, the higher work hardening ability, the larger amount of retained austenite transforming into martensite at the surface and the more stable untransformed retained austenite left in the top surface of the steel.

Experiment research on grind-hardening of AISI5140 steel based on thermal compensation

The grind-hardening process utilizes the heat generated to induce martensitic phase transformation. However, the maximum achievable harden layer depth is limited due to high grinding forces, and the tensile residual stress appears on the ground surface in the grind-hardening process. This paper proposes a new grind-hardening technology using thermal compensation. The workpiece of AISI5140 steel is preheated by electric resistance heating, and ground under the condition of the workpiece temperature 25°C, 120°C, 180°C and 240°C. The grinding force, harden layer depth and surface quality including residual stress on ground surface, surface roughness and micro-hardness are investigated. The experimental results show that a deep harden layer with a fine grain martensite can be obtained with the thermal compensation. The ground workpiece surface produces a certain compressive residual stress, and the residual compressive stress value increases with preheating temperature. As the preheating temperature increases, grinding force slightly decreases, while there is slightly increment of surface roughness. Compared with the conventional grind-hardening process, both the harden layer depth and residual stress distribution are significantly improved.

SiO2 substrate and Mo,In codoping effect on crystalline and vibrational characteristics of ZnO sprayed thin films

Undoped ZnO and codoped ZnO:Mo:In thin films were deposited on an amorphous SiO2 substrate at 460°C using a (Mo/Zn) molar ratio of 1% and (In/Zn) ratios of 1%, 2%, 3% and 10%. The thin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy (RS). The results revealed that the average crystallite sizes ranged from 36.2 to 18.97nm, decreasing uniformly with the increase of co-doping. They were also lower than the grain size values of 48.29, 51.38, 60.59, 36.76, and 54.52nm and dependent on the evolution of the residual compressive stress values, namely 0.358, 0.314, 0.569, 0.278 and 0.108GPa, without and with the co-doping, respectively. The non-uniformities recorded at In 2% could presumably be attributed to the variable effect of the SiO2 substrate and dopants on the formation of ZnO:Mo:In thin films. Raman spectroscopy confirmed the findings from structural analysis, showing that all samples crystallized following the hexagonal Wurtzite single phase. It highlighted the presence of two dominant bands, 1LO and 2LO, whose ∼71 and 137meV energies were comparable and above the ZnO exciton binding energy of 60meV. The 2LO band showed marked dependencies on the physicochemical parameters mentioned above. The strong bands noted for optimal co-doping at Mo 1% and In 3% can be used (tested) in various electrical and optoelectronic applications.

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4±0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 μm. Residual stresses attributed to γ-Al2O3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2ψ method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667±20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

An Investigation for Surface Integrity of Al<sub>2</sub>O<sub>3</sub>/A356 Composites Using Roller Burnishing Process on a Milling Machine

Roller burnishing process was applied to Al2O3/A356 composite specimens. The process was carried out on vertical milling machine. Effects of the burnishing process with varying process parameters on the characteristics of the machined surface and sub-surfaces were investigated. Residual stress distribution at different depths beneath the burnished surfaces, microhardness distribution, surface roughness were used as criteria to obtain the optimum burnishing conditions that give burnished surfaces with high integrity for the Al2O3/A356 composite. Results showed an improvement in surface characteristics of Al2O3/A356 composites using burnishing process. The better surface roughness was obtained with double passes burnishing, depth of penetration of 0.12 mm, and burnishing speed of 72 mm/min. Increase of number of burnishing passes increases the value of residual compressive stress and the microhardness at the burnished surface and subsurface. The microhardness slightly decreased with the increase of burnishing speed.

Incorporated W Roles on Microstructure and Properties of W-C:H Films by a Hybrid Linear Ion Beam Systems

W-incorporated diamond-like carbon (W-C:H) films were fabricated by a hybrid beams system consisting of a DC magnetron sputtering and a linear ion source. The W concentration (1.08~31.74 at.%) in the film was controlled by varying the sputtering current. The cross-sectional topography, composition, and microstructure of the W-C:H films were investigated by SEM, XPS, TEM, and Raman spectroscopy. The mechanical and tribological properties of the films as a function of W concentration were evaluated by a stress-tester, nanoindentation, and ball-on-disk tribometer, respectively. The results showed that films mainly exhibited the feature of amorphous carbon when W concentration of the films was less than 4.38 at.%, where the incorporated W atoms would be bonded with C atoms and resulted in the formation ofWC1-xnanoparticles. The W-C:H film with 4.38 at.% W concentration showed a minimum value of residual compressive stress, a higher hardness, and better tribological properties. Beyond this W concentration range, both the residual stress and mechanical properties were deteriorated due to the growth of tungsten carbide nanoparticles in the carbon matrix.

Simulation of Residual Stress Field of Diagonal Laser Shock Processing

Laser shock processing (LSP) is an innovative surface treatment technique. According to the theory of residual stress field formation by laser shock wave, laser overlapping shock processing of LY12CZ aluminium alloy was analyzed. The diagonal shock process is simulated by FEM using LS-DYNA codes, and the residual stress field in different angle of fall and pressure are predicted. The results indicate that the value of residual tension stress can be increased when diagonal shock, and the value of residual compressive stress will be decreased. The simulated results can provide the basis for experimental studying the diagonal laser shock processing and laser facular overlap.