Compressive Residual Stress Research Articles

Surface mechanical property and residual stress stability of nanostructured CNT/Al-Cu-Mg composites induced by shot peening

Shot peening (SP) is recognized for its capacity to enhance surface strength and induce compressive residual stresses (CRS). Nevertheless, quantifying the mechanical property improvements in thin shot peened layers remains challenging with traditional methods. In this study, CNT/Al-Cu-Mg composites were subjected to shot peening. The microstructure evolution of the peened layers along the layer depth direction was investigated by XRD and TEM. Meanwhile, the changes in the mechanical properties of the shot peened layers and the release rules of CRS during tensile cycling at different numbers loads were measured by an in-situ X-ray stress analyzer and a micro-tensile device in conjunction with the Von Mises stress criterion. The results showed that SP generated the nano-gradient deformation layer with nanograins size of 50–100 nm near the surface. The yield strength of the surface layer was increased from 352 MPa before SP to 435 MPa, an increase of 23.6 %. Moreover, the observation of fracture morphology indicated that SP reduced the material plasticit moderately and the agglomeration of the Al2Cu. In addition, in the case of a certain CRS on the initial surface, the relaxation of CRS was correlated with the magnitude of applied loads and the number of cycles and couldn't occur when the applied loads is below a specific value.

Effects of Beads and Shot Peening Intensity on the Surface Integrity and Fatigue Performance of a Stainless Gear Steel

Shot peening was performed on stainless gear steel using multiple kinds of beads at multiple intensities. The effects of shot peening on surface integrity and the rotational bending fatigue performance were tested with the crack origin location observed. The results showed that the average surface roughness increases from Sa0.408 μm to Sa1.165 μm as the shot peening intensity increases, which does not necessarily lead to an increase in surface stress concentration coefficient. The compressive residual stress profile and the depth of the hardened layer increase with the increase of shot peening intensity. During ceramic bead peening, the fatigue improvement, with a maximum of 25 times, increases with the raise of intensity (0.06–0.20 mmA), while the fatigue improvement decreases when intensity (0.2–0.30 mmA) increases using cast steel shot. Based on ceramic shot peening, a method was proposed to predict the origin location of rotational bending fatigue cracks of gear stainless steel, in which the effects of surface stress concentration, compressive residual stress, and external load introduced were all considered. By using the superposition method of external load and residual stress, the maximum actual stress corresponding depth is obtained, which is the origin position of the rotational bending fatigue crack.

Machine learning powered predictive modelling of complex residual stress for nuclear fusion reactor design

Fusion In-vessel components, assembled and maintained using laser welding, one of the most promising techniques, exhibit complex distributions of residual stress, microstructures, and material properties. These residual stresses can compromise structural integrity and lifespan of critical components. Although using advanced experimental measurements can evaluate the residual stress for individual case, extending the measurements to massive number of components are costly and time-consuming. Traditional machine learning (ML) models struggle to account for the heterogeneity and anisotropy of these stress distributions. Here, we develop a novel ML framework based on the Eurofer97 steel, the structural material for in-vessel components. The ML framework is trained on high-resolution residual stress data derived from recently-developed evaluation techniques. Combining with microstructures, the model enables prediction of heterogenous and anisotropic residual stress distribution. It successfully predicts the compressive residual stress in fusion zone (∼−200 MPa) balanced by tensile residual stress in heat affected zone (∼300 MPa), aligning closely with experimental results with the R-squared value of 0.989 and the mean square error of 10−4. Unlike experiments that take hours, the ML model provides predictions within seconds. It offers valuable insights into residual stress prediction for various joints, enhancing the reliability and lifetime prediction of in-vessel components.

Effects of laser shock peening on silicon nitride ceramic with varying sintering additive ratios

Silicon nitride ceramic (Si3N4) for industrial applications is conventionally manufactured with sintering additives, and the properties of Si3N4 change significantly based on the contents of these additives. In this study, we investigate the effects of laser shock peening (LSP) on Si3N4 sintered with varying ratios of sintering additives.The Si3N4 samples were sintered with a mixture of Y2O3, MgO, and SiO2 sintering additives at 5, 7, 9, and 11 wt%. A Nd:YAG laser (wavelength = 532 nm, maximum pulse energy = 1.4 J, repetition rate = 10 Hz, pulse duration = 8 ns, beam diameter = 11 mm, top-hat profile) was used to irradiate the Si3N4 samples. The samples were coated with a protective layer (100 μm thick aluminum foil) and a water layer to confine plasma. LSP of Si3N4 with 5% sintering additives resulted in a slight change in surface hardness but a 77% decrease in surface compressive residual stress. In contrast, LSP of Si3N4 with 11% sintering additives led to a simultaneous increase in surface hardness (7.3%) and surface compressive residual stress (67%), indicating a significant difference in the effectiveness of LSP depending on the ratio of sintering additives. Additionally, the surface of Si3N4 with 11% sintering additives showed evidence of grain refinement after LSP. It was demonstrated that the bending strength of Si3N4 with 11% sintering additives increased by 15.2%, and the depth of the fracture origin was significantly deepened.

Effect of Al Element on Retained Austenite, Residual Compressive Stress, and Contact Fatigue Life of Carburized and Quenched 20MnCr5 Steel Gear

To improve the contact fatigue life of gears, we studied the effect of adding a certain proportion of the Al element to a 20MnCr5 steel FZG spur gear under different heat treatment processes, characterizing the retained austenite and residual compressive stress on the tooth surface. The stability of the microstructure grain size on the gear surface under different heat treatment processes was studied, and the surface microstructure, phase structure, and composition of the gear were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The changes in the retained austenite content and grain size on the gear surface at a microscale of 2–100 μm were investigated. In addition, this study revealed the effect of adding the Al element and the optimization of the carburizing and quenching process on the residual compressive stress on the gear surface at a depth range of 200–280 μm. The effect of higher residual compressive stress and fewer non-metallic inclusions on the gear surface on the stress intensity factor of fatigue crack propagation was considered, along with the effect of deeper hardened layers on the improvement in wear resistance. The experiments in this study significantly improved the contact fatigue life of 20MnCr5 steel gears.

Study on Microstructure and Corrosion Fatigue Resistance of 14Cr12Ni3Mo2VN Materials Based on the Composite Technology of High-Frequency Induction Quenching and Laser Shock Peening

This study investigated the microstructure, microhardness, and residual compressive stress of 14Cr12Ni3Mo2VN martensitic stainless steel treated with high-frequency induction quenching (HFIQ) and laser shock peening (LSP). Using rotating bending corrosion fatigue testing, the corrosion fatigue performance was analyzed. Results show that a microstructural gradient formed after HFIQ and LSP: the surface layer consisted of nanocrystals, the subsurface layer of short lath martensite, and the core of thick lath martensite. A hardness gradient was introduced, with surface hardness reaching 524 Hv0.1, 163 Hv0.1 higher than the core hardness. A residual compressive stress field was introduced near the surface, with a maximum residual compressive stress of approximately −575 MPa at a depth of 0.1 mm. Corrosion fatigue results indicate that cycle loading times of samples treated with HFIQ and LSP were 2.88, 2.04, and 1.45 times higher than untreated, HFIQ-only, and LSP-only samples, respectively. Transmission electron microscopy (TEM) characterization showed that HFIQ reduced the lath martensite size, while the ultra-high strain rate induced by LSP likely caused dynamic recrystallization, forming numerous sub-boundaries and refining grains, which increased surface hardness. The plastic strain induced by LSP introduced residual compressive stress, counteracting tensile stress and hindering the initiation and propagation of corrosion fatigue cracks.

Investigation on the Cutting Performance of High‐Speed Dry Milling for 30CrMnSiNi2A Steel

High‐speed dry milling (HSDM) technology is one of the most attractive solutions for improving the cutting performance of difficult‐to‐machine materials. However, the study of HSDM performance for 30CrMnSiNi2A steel has not been reported. In this article, HSDM for 30CrMnSiNi2A steel is investigated using TiN‐coated and AlTiN‐coated tools, focusing on cutting force, vibration, surface roughness, residual stress, and tool wear. The effects of cutting parameters on cutting force and vibration are remarkably similar. At a spindle speed of 7500 r min−1, both cutting force and vibration are minimized. TiN‐coated and AlTiN‐coated tools exhibit distinct performance differences. But, HSDM of 30CrMnSiNi2A steel using TiN‐coated and AlTiN‐coated tools can achieve low surface roughness. The depth of cut significantly affects surface roughness, which is lowest at the depth of cut (0.8 mm). Most of the workpiece surface shows residual compressive stress. The main wear mechanisms for both coated tools are abrasive wear, adhesive wear, and oxidative wear. Furthermore, the AlTiN‐coated tool is more wear resistant on the flank face compared to the TiN‐coated tool. Chipping due to crater wear is the leading cause of tool failure for the AlTiN‐coated tool. Upon various comparisons, the AlTiN‐coated tool is more suitable for HSDM of 30CrMnSiNi2A steel.

Preparation and Properties of Thick Tungsten Coating Electrodeposited from Na2WO4-WO3-KCl-NaF Molten Salt System

The pulsed current electrodeposition method was employed for the first time to achieve tungsten coating with a thickness of 433.72 μm on a CuCrZr alloy from Na2WO4-WO3-KCl-NaF molten salt. The microstructure of the coating was observed and the coating density, porosity, hardness, bonding strength, residual stress and oxygen content were tested. The results revealed that the tungsten coating exhibited desirable characteristics such as high density, absence of impurities, excellent adhesion to the matrix (53.16 MPa), residual compressive stress as surface stress, and good stability and durability. Moreover, this thick tungsten coating possesses high density and hardness, low oxygen content and porosity. This offers a novel solution to solve the challenging issue of the connection between tungsten material and heat sink material.

Residual Stress Analysis in High‐Speed Physical Vapor Deposition Coatings

Several studies focus on impact of residual stress in coatings, predominantly those synthesized by conventional physical vapor deposition (PVD) techniques like arc PVD and magnetron sputtering. High‐speed PVD (HS‐PVD) is based on hollow cathode gas flow sputtering, enabling the deposition of thick coatings s > 20 μm in contrast to the mentioned processes, where coating thickness is limited due to compressive residual stresses. Therefore, the effect of residual stresses on HS‐PVD coatings and adhesion was analyzed for the first time. The aim is to evaluate the influence of diverse substrate materials, different coating systems, and process parameters on the residual stress states in HS‐PVD coatings. Different coating systems like AlCrN and AlCrO are deposited at different reactive gas flows, coating times, and bias voltages. The residual stress of oxide coatings, deposited on cemented carbide and steel X40CrMoV5–1, is analyzed using X‐ray diffraction (XRD) and the sin2ψ method. For AlCrN coatings, in addition to the XRD method, the residual stresses are measured by focused ion‐beam‐digital image correlation ring‐core method to investigate different measuring methods. Both coating systems show higher adhesion strength with increasing thickness. Lower residual compressive stresses are unexpectedly observed at higher coating thickness using both analysis methods.

A Time‐Saving Method for Evaluating the Fatigue Strength of Carburized High‐Alloy Steel Containing Carbides

To propose a time‐saving method for evaluating the fatigue strength of carburized steel, the fatigue behavior and fracture mechanism of carburized 14Cr14Co13Mo5 steels are studied by the rotary bending fatigue tests. It is found that the fatigue crack initiation site changes from surface to internal after carburizing due to the residual compressive stress and carbide cluster caused by the carburization. Besides, a notable correlation between the stress intensity of the cracked carbides at fatigue crack initiation site and fatigue life is observed in the carburized samples. This correlation allows for the estimation of fatigue strength at long conditional life based on samples tested at relatively high stress amplitudes with short lives, achieving a prediction error within 10% for the material studied. A significant time saving of ≈65% compared to the staircase method is achieved. The proposed method has significant implications for improving the efficiency fatigue strength evaluation in carburized steels containing carbides.

Enhancing turbine blade durability: Evaluating protective ceramic coatings for Ti6Al4V alloy

Ti64 turbine blades face extreme conditions during solid particle erosion, accelerating the erosive and corrosive processes. Hard-coating materials such as DLC, AlTiN, TiSiN, AlCrN, and AlTiCN have been introduced through physical vapor deposition to enhance the turbine blade characteristics and increase the component lifespan. The results showed preferential orientations of (002) and (022) in coating crystallization with DLC exhibiting the highest compressive residual stress. DLC and AlTiCN coatings demonstrated fewer macroparticles and white spots, correlating with a lower coefficient of friction (COF) and surface roughness. The wear analysis revealed that DLC had the lowest COF and wear rate, followed by AlTiCN. Electrochemical tests indicated DLC's superior corrosion resistance of DLC. Although the properties of AlTiCN are comparable, DLC has emerged as the most promising coating material for achieving high erosion particle resistance in Ti64 turbine blades.

Influence of material orientation, loading angle, and single-shot repetition of laser shock peening on surface roughness properties

Titanium alloy Ti6Al4V is extensively utilized in biomedical applications due to its excellent biocompatibility, corrosion resistance, and mechanical properties. The design of dental implant surface textures has changed throughout time to address issues with oral rehabilitation in both healthy and damaged bones. The longevity of an implant is significantly impacted by surface roughness. This study examines the use of laser shock peening (LSP) as a surface modification technique to improve the mechanical properties of implants. A numerical model is developed using the commercial finite elements software in ABAQUS/Explicit for simulating dynamic conditions. The aim of the study is to develop surface roughness parameters using computational methods such as studies have not yet been contemplated. The single shot angle, shot repeat, time, material orientation, and laser power are applied for the first time simultaneously to evaluate the impact of material orientation and loading angles on surface roughness parameters. The study showed that the developed computational model’s compressive residual stress was −578.45 MPa, while the experimental samples were −592.18 MPa. Consequently, the difference between the computational and experimental results was 2.32%. Without regard to material orientation or angle, the compressive residual stress of the samples under examination was found to be −578.450 MPa after three repetitions and to decreased to −1.620 MPa after four. These results demonstrate that by varying the material orientation and loading angle, the Ra value may be increased four times.

Production and Forming of Deposition‐Welded Hybrid Multimaterial Shafts

The combination of several materials in one component can contribute to increased performance. Herein, three types of hybrid components are manufactured using two cladding processes and one joining process. The resulting workpieces are then formed and tested to determine the potential of the different material combinations. Two types of workpieces are produced to investigate multilayer claddings made of different materials, which serve to positively adjust the residual stress. The workpieces are tested using microstructural images and hardness measurements to characterize the microstructure and properties of the intermediate layers. In addition, residual stress measurements are carried out to determine the residual stress ratios. Compressive residual stresses are present in the subsurface of the welded and subsequently formed layer, which will improve the service life in case of rolling load conditions. The third type of workpiece is a combination of aluminum alloy and steel with a cladding layer that combines the performance of the cladding material in the bearing seat with the weight reduction of the aluminum alloy. Scanning Electron Microscopy (SEM) measurements are used to determine whether the application of the cladding has an influence on the intermetallic phase seam in the joining zone of aluminum alloy and steel.

An Experimental Investigation into the Enhancement of Surface Quality of Inconel 718 Through Axial Ultrasonic Vibration-Assisted Grinding in Dry and MQL Environments

Ultrasonic vibration-assisted grinding (UVAG) has proven to be beneficial for grinding difficult-to-machine materials. This work attempts to enhance the grinding performance of Inconel 718 through a comprehensive study of UVAG characteristics. Grinding experiments were performed in both dry and Minimum Quantity Lubrication (MQL) environments, and assessment of the grinding forces, specific energy, residual stress, and surface topography was done. A substantial reduction of both surface roughness and grinding force components was observed in UVAG compared to conventional grinding (CG). Utilizing UVAG with MQL at the maximum vibration amplitude led to a 64% reduction in tangential grinding force and a 51% decrease in roughness parameter, Ra, when compared to CG conducted in a dry environment. The high-frequency indentations of the abrasives in UVAG generated compressive residual stresses on the ground surface. Surface parameters pointed to uniform texture and SEM images showed widening of abrasive grain tracks on the workpiece surface during UVAG. The utilization of UVAG under MQL produced a synergistic impact and resulted in the lowest grinding forces, specific energy, and optimal surface quality among all the grinding conditions investigated. Overall analysis of the results indicated that the axial configuration of the vibration set-up is favorable for UVAG, and the high-frequency periodic separation-cutting characteristic of the process improves lubricating efficiency and grinding performance.

Effect of ultrasonic vibration on fatigue life of Inconel 718 machined by high-speed milling: Physics-enhanced machine learning approach

Ultrasonic assisted high-speed machining (UAHSM) can be served as a thermomechanical surface sever plastic deformation (SSPD), because of the high-frequency impact load exerting to the sample together with thermomechanical loads due to shearing and plowing. Despite existing of few works which studied the impact of ultrasonic vibration on fatigue life assessment of difficult-to-cut material by experimental approach, they couldn’t provide an in-depth analysis to identify the underlying mechanisms of fatigue due time-consuming and costly fatigue life tests. Hence, elucidating the role of ultrasonic vibration in UAHSM on variation of fatigue life needs further studies. In order to do so, in the present work, a hybrid predictive approach based using ANFIS-based machine learning model and micromechanical Navaro-Rios (NR) fatigue crack propagation model has been introduced to directly correlates the UAHSM’s parameters to fatigue life. Here the former correlates feed rate, cutting velocity and vibration amplitude as process inputs, to surface integrity aspects (SIA) viz residual stress, roughness and grain size as output. Then, the modeled SIA are correlated to fatigue life using the former. The introduced hybrid model was then verified through series of UAHSM by examining the fatigue lives of milled Inconel 718 using four-point bending fatigue tests. Upon confirmation of the developed model, a comprehensive study was carried out to find how the process factors impact variation of SIA and subsequently fatigue. It was found from the results of developed models and confirmatory experiments that the role of ultrasonic vibration on improved fatigue life is mainly due to inducing compressive residual stress and more refined microstructure than the roughness.

Improvement of Fatigue Characteristics of Friction Stir Welded A6061-T6 Applying Shot Peening

Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (ahml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between ahml and the maximum detectable crack depth (aNDI) by non-destructive inspection (NDI).

Effect of ultrasonic shot peening on the microstructure, surface residual stress, and wear properties of Ti-6Al-4V alloy

In this study, ultrasonic shot peening (USP) was used to enhance the surface of a Ti-6Al-4V alloy. Samples treated with different amplitudes were characterized and their wear resistance was tested and analyzed. The results demonstrate that the surface morphology of the Ti-6Al-4V alloy changed significantly after USP treatment, and the surface roughness increases at first, then stabilizes as the amplitude increases. The surface grain of the material is refined due to severe plastic deformation, and the average grain size after USP treatment is 27.93% finer than the original sample. Due to the effect of fine grain strengthening and work hardening, the microhardness of the material's near-surface layer is also enhanced in varying degrees, showing a gradient decrease throughout the depth of the cross-section. Furthermore, USP produces compressive residual stress as high as −791.01 MPa in the near-surface layer. When the USP amplitude is 80% and the treatment time is 240 s, the wear resistance of Ti-6Al-4V alloy is substantially enhanced under the combined action of hardness, compressive residual stress, and surface pits, reducing wear resistance. The wear mechanism is primarily abrasive wear and oxidation wear.

Gradient nanostructure enabled exceptional fretting fatigue properties of Inconel 718 superalloy through submerged abrasive waterjet peening

Submerged Abrasive Waterjet Peening (SAWJP) shows great application potential in augmenting the fatigue properties of metallic parts. Thus, the present work aims to investigate the influence of SAWJP on the Surface Integrity (SI) and Fretting Fatigue (FF) properties of Inconel 718 (IN718) superalloy and illustrate the microstructural evolution, FF life improvement, and fretting wear mechanism. First, the SI of the IN718 specimen was examined following treatment via SAWJP. Results showed that the specimen subjected to SAWJP formed a total plastic deformation layer of 56 μm. The maximum microhardness and Compressive Residual Stress (CRS) measured across the depth of the SAWJP-treated specimens exhibited an increase in values ranging between 522 and 541 HV and 1171–1380 MPa, respectively. The FF test results of the specimen before and after SAWJP treatment at ambient temperatures indicated that the FF life of the SAWJP-treated specimen surpassed that of the as-received specimen by a factor of 2.81. The examination of the FF fracture, contact surface, and crack propagation behavior revealed the crucial factors contributing to the enhanced FF resistance of the IN718 specimen, including the gradient nanostructure characterized by ultra-refined grains, substantial CRS, and elevated microhardness, which were all induced by the SAWJP treatment.

Microstructure and mechanical performance of cold spray Cr coatings

Cold spray deposition has emerged as a promising method for applying protective coatings in the nuclear industry, particularly for enhancing the accident tolerance of fuel assemblies. In this process, helium gas is often used to propel solid powder particles towards the target substrate, however, nitrogen gas is also considered due to its significantly lower cost. In this study, we investigate the influence of nitrogen and helium gas as propellants on the properties and microstructure of pure chromium (Cr) coatings on zirconium (Zr) alloy cladding tubes. Employing Scanning Electron Microscopy (SEM) and electron and x-ray diffraction techniques (EBSD, XRD), we explore the structural characteristics of the coatings. Additionally, in-situ SEM tensile testing at room temperature, coupled with Digital Image Correlation (DIC), is utilized to assess the coating cracking behaviour. Our findings reveal distinct differences in coating morphology and residual stress between nitrogen and helium propelled Cr coatings. The nitrogen-propelled coating exhibits a more porous structure with smoother coating/substrate interfaces and lower compressive residual stress compared to the helium-propelled one. This results in earlier strain-induced crack initiation and higher crack density at lower strains (0.5–2%). However, at higher strains (2–5%), both coatings demonstrate identical crack saturation densities (saturated number of cracks per unit length), accompanied by similar crack toughening mechanisms and evidence of shear strain bands at intercrack regions, indicative of plasticity onset.

Strengthening Study on Microsphere Particle Peening for Flexspline Surface of Harmonic Reducer

Abstract The service stability of the flexspline directly affects the service life of the harmonic reducer. Its main failure modes are fatigue fracture of the flexspline, damage of the flexible bearing, tooth wear or transmission slip, the above problems are often sprouted and developed from the surface. Researches show the novel surface treatment technology-Microsphere Particle Peening can significantly enhance the surface performance of the flexspline of the harmonic reducer, and thus improve its fatigue resistance. Therefore, studying this novel shot peening technology has significant scientific significance and practical value. In this paper, Microsphere Particle Peening is adopted to strength the flexspline surface and the effects of three different Microsphere Particle Peening conditions on the surface performance of the flexspline is analyzed. The research results indicate that Microsphere Particle Peening technology can introduce larger residual compressive stress, reduce the surface roughness, increase the surface hardness, improve the microstructure morphology, and effectively control the deformation amount of the flexspline by controlling the processing parameters of Microsphere Particle Peening. Therefore, Microsphere Particle Peening technology has broad engineering application prospects in the surface strengthening of precision components.