Effect Of Compressive Residual Stress Research Articles

Effect of Surface Roughness and Compressive Residual Stress on the Fatigue Performance of TC4 Titanium Alloy Subjected to Laser Shock Wave Planishing

ABSTRACTThe milled surface of TC4 titanium alloy was treated by laser shock peening (LSP) and laser shock wave planishing (LSWP) to investigate the effect of compressive residual stress (CRS) and surface roughness (SR) on the vibration fatigue performance. The results demonstrate that although the amplitude of CRS induced by LSWP is lower than that of LSPed specimens, the vibration fatigue life of LSWPed specimens increased by 63.78% due to a significant reduction in SR from Sa 14.1 μm to Sa 4.21 μm. When the SR is low, increasing the amplitude of CRS is more advantageous to enhance fatigue life. The fractographic analysis further confirmed that compared with LSPed and T0.2‐LSWPed specimens, T0.1‐LSWPed specimens have considerably less initial fatigue crack initiation, and the crack initiation location is deeper. The fatigue striation spacing of T0.1‐LSWPed specimens is the smallest (0.25 μm), greatly lowering the fatigue crack growth rate.

Improvement of gradient microstructure and properties of wire-arc directed energy deposition titanium alloy via laser shock peening

Wire-arc directed energy deposition (WADED) technology has been widely used in the remanufacturing of titanium alloy structural components benefited from with the advantages such as high deposition efficiency and low cost. However, due to the coarse and anisotropic microstructure, the complex internal stresses and processing-induced rough surface significantly reduce fatigue performance and reliability of the remanufactured structural components. In this work, surface modification of titanium alloy WADED repair component was carried out via laser shock peening (LSP), and its gradient structure, microhardness, residual stress and fatigue performance and enhancement mechanism were systematically investigated. Results indicated that the different microstructure of each region led to different responses under the action of LSP, which was related to the change of dislocation density. LSP induced crystal defects such as high-density dislocations, twins and stacking faults on the surface. A variety of crystal defects gradually decreased with the depth from the strengthened surface, formed a gradient microstructure and significantly affected the microhardness and residual stress of the repaired components. The surface hardness and compressive residual stress of the repaired components were greatly increased after LSP and the hardened layer and compressive residual stress depth affected layer were 600 μm and 800 μm, respectively. The average fatigue life of the additive repair component increased by 197 % under the synergistic effect of compressive residual stress and gradient microstructure.

Wet shot peening effects on surface integrity and very high cycle fatigue of TC17 titanium alloy

With the increasing reliability requirements of aerospace equipment, very high cycle fatigue of TC17 titanium alloy has gained significant attention. This study investigates the effects of different wet shot peening treatments on the surface integrity and very high cycle fatigue performance of TC17 titanium alloy, elucidating the underlying mechanisms. Experimental results show that wet shot peening exacerbates surface defects, increases roughness, creates a plastic deformation layer, and induces compressive residual stress and work hardening. The combined effect of these factors reduces the fatigue performance. However, post-peening polishing significantly enhances the very high cycle fatigue performance by reducing stress concentration from surface defects while retaining the beneficial effects of compressive residual stress. Therefore, polishing after wet shot peening is concluded to be the most effective method for improving the very high cycle fatigue performance of TC17 titanium alloy.

Fatigue life prediction model for shot-peened laser powder bed fused 304L steel considering residual stress relaxation and defect distribution

Shot peening (SP) is a post-treatment technology that enhances the surface smoothness, mechanical properties, and fatigue performance at the surface layer of metal materials produced through laser powder bed fusion (LPBF). Therefore, accurate life prediction is crucial to effectively design and evaluate the SP process and enhance fatigue life. This study employs a cost-effective and efficient analytical method to investigate relaxation in residual stress (RS). The method calculates the interaction between RS in SP and external loading and combines it with a life prediction model. In addition, a defect-based parameter area is employed to characterize the impact of the effective defect dimensions on the fatigue life of LPBF materials. The effects of compressive residual stress (CRS) introduced by SP and process-induced internal defects on the fatigue life of LPBF material are investigated via a modified Goodman‐Basquin model. The fatigue life of 304L stainless steel (SS) prepared by LPBF after SP is predicted, and good consistency between measurement and prediction is observed.

Quantitative evaluation of residual stress and microstructural effects on the surface hardness of machined Ti-6Al-4 V alloy with microscopic characterization techniques

The surface hardness of machined Ti-6Al-4 V components has a significant influence on the service performance and fatigue life. It’s acknowledged that the hardness value of machined surface is dependent on microstructure and residual stress, however, the quantification of their influence levels on surface hardness is still an unresolved issue, which limits the potential for further enhancing the mechanical property of machined parts. Furthermore, it’s difficult for current studies to fully reveal the mechanism of hardness fluctuation due to release of residual stress. To address these gaps, this study presents a novel method for quantitatively evaluating residual stress and microstructural effects on the machined surface hardness using microscopic characterization techniques. The microstructures of machined Ti-6Al-4 V workpiece were characterized by electron backscatter diffraction (EBSD), and the microstructural hardening effects were analyzed. The residual stresses release and evaluation were performed by the Focused Ion Beam-Digital Image Correlation (FIB-DIC) ring core method, then the surface hardening originated from residual stress and microstructural effects can be assessed by nano-indentation measurements. The results show that the surface hardness increase induced by the combined effects of compressive residual stress and microstructure, where the microstructural hardening can be strengthening by obtaining smaller grain size and high proportion low grain boundary, and the higher magnitudes of compressive residual stress can also enhance the hardness increase. The surface softening induced by compressive residual stress relaxation with no obvious microstructural alterations was observed and the maximum softening reached 14.54% in this study. The findings are beneficial for understanding the mechanical property strengthening mechanism of the machined parts.

Biodegradation performance of ball burnished magnesium alloy in stimulated body fluids for bioresorbable implant applications

Magnesium alloys are found to be potential bioresorbable materials. However, the application range of these alloys as bioresorbable materials has been limited due to rapid degradation in physiological fluids. The current study deals with the enhancement of degradation behavior of Mg Ze41A alloy in SBF solution by ball burnishing. Further, the influence of burnishing parameters on biodegradation rate has been investigated by Tafel plots, polarization resistance, electrochemical impedance spectroscopy and surface morphology analysis of degraded samples. Additionally, the biodegradation rate has been estimated by ANFIS modeling. The biodegradation rate of Mg Ze41A has been reduced from 1.106 mm/yr to 0.367 mm/yr with an improvement of 68.82% at optimum burnishing condition of burnishing force 50 N, burnishing speed 1400 RPM, burnishing feed 125 mm/min and 2 passes. ANOVA analysis has revealed that burnishing force and feed have contributed the most for the enhancement. The shift in degradation potential towards noble direction and reduction in degradation current density in potentiodynamic polarization curves and the highest charge transfer resistance in electrochemical impedance spectroscopy of the burnished samples are observed for burnished samples. The results reveal that ball burnishing process is a potential surface modification method in reducing the biodegradation rate of Mg Ze41A alloy. The ball burnishing has resulted in lowest biodegradation rate at a degradation current density of 5.743 μA/cm2 and degradation potential of −1.513 V. The ANFIS model developed with 81 fuzzy rules and triangular membership function estimated the biodegradation rate with an accuracy of 95.03%. The decrease in biodegradation rate of ball burnished magnesium substrate in SBF is essentially due to cumulative effect of compressive residual stress, microhardness, surface finish, work hardening and grain refinement.

Effect of laser shock peening on surface integrity and tensile fatigue behavior of TB8 bolts

Laser shock peening (LSP) treatment was introduced to improve tensile fatigue behavior of TB8 titanium alloy bolt. TB8 bolts surface integrity, tensile fatigue fracture and strengthening mechanism after LSP treatment were systematically investigated. Results showed that cracks and machining defects on the thread surface were eliminated, surface layer microhardness and compressive residual stress were increased after LSP treatment. Meanwhile, the grains sizes of the LSP treated bolts samples were reduced to 38.61 μm with the formation of high density dislocations. LSP treated bolts samples with 80 mJ laser energy exhibited the maximum average tensile fatigue life, which was increased from 66,452 cycles to 81,319 cycles. In addition, under the synergistic effect of compressive residual stress and grains refinement, cracks propagation path was changed, which were the primary factors for the improvement of TB8 bolt tensile fatigue life.

The Effects of Compressive Residual Stress on Properties of Kyanite-Coated Zirconia Toughened Alumina Ceramics.

In this study, the prestressed coating reinforcement method was employed to create kyanite-coated zirconia toughened alumina (ZTA) prestressed ceramics. Due to the mismatch of the coefficient of thermal expansion (CTE) between the coating and substrate, compressive residual stress was introduced in the coating. The effects of compressive residual stress on the mechanical properties of ZTA have been demonstrated. Results show that the flexural strength of the kyanite-coated ZTA ceramics improved by 40% at room temperature compared to ZTA ceramics. In addition, the temperature dependence of mechanical properties has also been discussed. And the results show that the reinforcement gradually diminished with increasing temperature and eventually disappeared at 1000 °C. The modulus of elasticity of the material also exhibits a decreasing trend. Furthermore, the introduction of the prestressing coating enhanced the thermal shock resistance, but the strengthening effect diminished as the temperature increased and completely disappeared at 800 °C.

Simulation of residual stress and micro-plastic deformation induced by laser shock imprinting on TC4 titanium alloy aero-engine blade

In laser shock processing (LSP) of aero-engine blades, overlap marks due to spot overlapping cause irregular surface morphology that becomes a source of cracks under fatigue behaviors. This reduces the beneficial effect of compressive residual stress induced by LSP and undermines fatigue performance of blades. In this paper, laser shock imprinting (LSI) is proposed to improve fatigue performance of aero-engine blades. In this process, a layer of contact film with micro-grooves is placed between the absorption layer and the workpiece (blade) of the LSP. By using the double action of laser shock wave and micro-grooves in contact film, blade surface morphology is transformed towards the direction conducive to improve its fatigue performance. Using ABAQUS software, Johnson-Cook model and Fabbro model were considered to study the plastic rheological behavior of blade surface material induced by LSI. Effect of process parameters namely, peak pressure, impact number and spot overlapping ratio on residual stress and micro-plastic deformation of blade surface were studied. Simulation results showed that under the action of laser shock wave, blade surface material flowed into micro-grooves in contact film via extrusion plastic deformation. This resulted in micro-bulge morphology having geometrically specific arrangement on blade surface, which achieved accurate control of micro-plastic deformation on blade surface. Increase in peak pressure and impact number increase the surface micro-bulges height. However, increase in peak pressure lowers the stress difference between bulging edge and non-bulge zones. It was found that 33% spot overlapping impact resulted in more uniform surface micro-bulge morphology on blade surface.

Effect of compressive residual stress and press fitting on residual life assessment of deep-rolled EA4T steel railway axles

Deep rolling surface strengthening is an effective way to introduce compressive residual stress (CRS) along the railway axle, which can improve the fatigue resistance of the material. The CRS field was rebuilt adopting the proportional-integral (PI) iteration method and the unit pressure method (UPM) to study the fatigue cracking behavior of deep-rolled EA4T railway axles. The remaining life prediction model and the stress intensity factor (SIF) solution method were then validated using simulations and testing with small-sized specimens. The remaining life of the EA4T railway axle was then calculated by applying a realistic vertical load spectrum. The results showed that CRS prevented crack propagation, enhanced the critical propagation size of railway axle cracks, and prolonged the remaining life of the axle. Additionally, the remaining life of the axle may not support the following maintenance period if a crack with an extendable size emerges at the unloading groove of the railway axle. This work provides a theoretical basis for the optimization of the non-destructive testing (NDT) interval of deep-rolled EA4T railway axles.

Improving the high cycle fatigue property of Ti6Al4V ELI alloy by optimizing the surface integrity through electric pulse combined with ultrasonic surface rolling process

To improve the surface integrity and high cycle fatigue property of Ti6Al4V ELI alloy, the electric pulse has been introduced into the ultrasonic surface rolling process (USRP), which is called electric pulse-assisted ultrasonic surface rolling process (EUSRP). With the help of “electroplasticity” of the electric pulse, the thickness of the surface gradient deformation layer was about three times of the USRP specimens by adjusting the pulse current level. However, the surface hardness decreases due to the continuous effect of the pulse current and the “skin effect” during treatment. It is worth noting that the higher the applied pulse current, the more severe the softening. This paradox causes the fatigue performance of EUSRP specimens lower than that of USRP specimens. To break this paradox, the EUSRP treatment is followed by a USRP treatment. The EUSRP-2 (with a pulse current of 200 A) +USRP specimens exhibit excellent surface hardness, a gradient deformation layer thickness of about 400 µm, low surface roughness and high compressive residual compressive stress. Besides, the hardening mechanisms of the different surface strengthening specimens have been quantitatively analyzed in combination with microstructure analysis. The fatigue life of Ti6Al4V ELI alloy can be improved by about 25 times at 780 MPa using the EUSRP-2+USRP treatment, the main reason for the highest fatigue life is the deepest surface gradient layer and the deepest crack initiation site. The fatigue limit of the EUSRP-2+USRP specimens is not the highest because too much surface hardening causes compressive residual stress relaxation during cycling and the beneficial effect of compressive residual stress is eliminated.

Corrosion and Electrochemical Properties of Laser-Shock-Peening-Treated Stainless Steel AISI 304L in VVER Primary Water Environment

Laser Shock Peening (LSP) is a surface treatment technique for metallic materials. It induces plastic deformation at the surface of up to around 1 mm in depth. This process introduces residual stresses that lead to strain hardening, and potentially improvements in fatigue, stress corrosion cracking (SCC) and general corrosion behaviour in many, but not all, corrosive media. In this paper, two specimens made of AISI 304L stainless steel, one LSP-treated and one un-treated, were tested at 280 °C and 8 MPa in VVER (or PWR) primary circuit water chemistry using in situ Electrochemical Impedance Spectroscopy (EIS). This experiment serves to qualify the influence of LSP on the changes in corrosion behaviour in high-temperature, high-density water. The residual stress (RS) measurement of the surface showed a compression RS. Before LSP treatment, RS at the surface was 52.2 MPa in the rolling direction 0°RD and 10.42 MPa in the transverse rolling direction 90°RD. After the treatment, surface RS was −175.27 MPa and −183.51 MPa for Scan and TScan directions, respectively. The effect of compressive RS at the surface was studied and showed an increase in corrosion rate. The analysis of oxide layer by SEM revealed differences between LSP-treated and untreated AISI 304L specimens and their connection to corrosion rates.

Effect of compressive residual stress on wear resistance of IGT25+ gas turbine compressor blades made of 1.4923 steel

Effect of compressive residual stress on wear resistance of IGT25+ gas turbine compressor blades made of 1.4923 steel

The Evolution of Micromechanical Properties for Zr-Based Metallic Glass Induced by Laser Shock Peening

The micromechanical properties of Zr-based metallic glass (MG) induced by laser shock peening (LSP) were studied through the use of nanoindentation. The serrations in representative load-displacement (P-h) curves exhibited a transformation from stairstep-like to ripple-shaped from untreated zone to shock region, which implied an increase in plastic deformation ability of material after LSP. Significant hardening was also observed in the impact zone, which can be attributed to the effect of compressive residual stress. Both increase in hardness and plastic deformation ability in shock region indicate the excellent effect of LSP on the micromechanical properties of investigated Zr-based MG, which provide a new way to study the deformation mechanism in metallic glasses and a further understanding of plasticization.

Mechanism study of the residual stress evaluation of low-carbon steels using the eddy current magnetic signature method

The eddy current magnetic signature (EC-MS) method is a relatively new method used to evaluate the residual stresses of ferromagnetic steels with higher sensitivity than other magnetic techniques. In this study, the effects of mechanical polishing and the ferrite–pearlite structure on the shape of the EC-MS signal were investigated in two experiments to clarify the effect of compressive residual stress on the EC-MS signal shape. In the first experiment, the work-hardened layers of the specimens were removed by electrolytic polishing and the EC-MS signals of the specimens were investigated. The second experiment involved the EC-MS measurements of materials with different pearlite contents, i.e., low-carbon steel with 0.17% and 0.27% carbon and pure iron. Specimens with different residual strains were prepared using a tensile test apparatus and their EC-MS signals were compared. In both experiments, the residual stresses acting on the specimens were measured adopting X-ray diffraction. The results reveal that the non-anisotropic compressive residual stress acting on the specimen surface changed the EC-MS signal in an anti-clockwise manner while the unidirectional compressive residual stress inside the specimen changed the EC-MS signal in a clockwise manner.

Recent Developments and Novel Applications of Laser Shock Peening: A Review

By inducing work hardening and beneficial compressive residual stresses in near‐surface regions, laser shock peening (LSP) improves the fatigue performance of many metallic components. In recent years, LSP has found many new applications in emerging fields: additive manufacturing, ceramics, and metallic glasses. In addition, innovative process development based on LSP has been reported, which includes warm LSP, cryogenic LSP, electropulsing‐assisted LSP, laser peening without coating, femotosecond LSP, and laser peen forming. Herein, a comprehensive review of the LSP process with a focus on the novel applications and innovative process development is aimed for. The history of LSP with key events is briefly reviewed. The fundamental mechanisms of LSP, including the generation of shockwaves by a high‐energy pulsed laser, the generation of compressive residual stresses by the shockwave, and its effect on crack propagation, and how LSP induces grain refinement are also discussed. The effects of compressive residual stresses and grain refinement on the mechanical properties of metallic materials are reviewed. Recent developments in LSP, such as innovative process development based on LSP and its novel applications, are discussed. Finally, the current challenges the LSP technology faces and its future directions are also discussed.

Improved Hydrogen Embrittlement Resistance of Steel by Shot Peening and Subsequent Low-temperature Annealing

The effect of shot peening and subsequent low-temperature annealing (SP treatment) on hydrogen embrittlement in tempered martensitic steel was investigated comparing the typical hydrogen charging methods, constant current controlled cathodic charging test and combined cyclic corrosion test (CCT). The hydrogen entry behavior was evaluated by hydrogen permeation technique and hydrogen visualization using secondary ion mass spectrometry. The SP treatment improved hydrogen embrittlement resistance in both hydrogen charging methods. On the other hand, the effect of SP treatment on the hydrogen entry was different depending on hydrogen charging method. The hydrogen entry was suppressed by SP treatment in the cathodic charging test because the compressive residual stress reduced hydrogen concentration in the surface layer and the potential increased by the increase of surface roughness and the formation of a surface film. In CCT, although the surface hydrogen concentration decreased due to compressive residual stress, the total hydrogen content did not decrease by SP treatment since the surface film disappeared by corrosion and an increase of surface roughness led to an increase in hydrogen entry sites. The improved hydrogen embrittlement resistance by the SP treatment in the cathodic charging test is a result of hydrogen entry suppression in addition to the effect of compressive residual stress. In CCT, the hydrogen embrittlement resistance was improved by SP treatment due to effect of compressive residual stress, i.e., the suppression of stress concentration as well as the stress-induced hydrogen diffusion in stress concentration area and the reduction of hydrogen concentration in the surface layer.

Improving reliability of high‐strength steel designed against fatigue limit using surface crack nondamaging technology by shot peening

AbstractRecently, surface crack nondamaging technology has been developed to render harmless surface cracks that can reduce the fatigue limit of metals by 20–60%. This is due to the effects of compressive residual stress induced by shot peening. To improve the reliability of high‐strength steel equipment designed against fatigue limit using surface crack nondamaging technology, the following characteristics were determined: (1) the effects of surface crack aspect ratio on maximum harmless crack depth (ahlm) at high‐strength steel for three residual stress distributions; (2) the relationship between the maximum allowable crack depth (acrN) and ahlm assuming the value of safety factor; (3) the relationship between minimum detectable crack depth via nondestructive inspection (aNDI) and ahlm, assuming that nondestructive inspection could detect the crack with sufficient probability; and (4) the relationships between ahlm, aNDI, and acrN.

Effect of Compressive Residual Stress on Film Formed by Mechanochemical Multifunction Cavitation Processing

Recently, mechanochemical multifunction cavitation (MC-MFC) was developed to improve the corrosion resistance of the magnesium surface. MFC is a technology that combines water jet peening and ultrasound cavitation. MC-MFC is a technology that adds phosphoric acid to water. It can improve the corrosion resistance by forming a phosphate film on the Mg surface. Conventional anodic oxidation, plating, and chemical vapor deposition can improve corrosion resistance by forming a film on the Mg surface, but it is difficult to improve characteristics such as compressive residual stress on the surface. MFC-treated surfaces have previously imparted various properties such as imparting compressive residual stress necessary to improve the fatigue strength to Al alloys and Cr-Mo steels. In this study, the effect of film formed on MC-MFC processed surface on compressive residual stress was investigated.

Fatigue performance of laser shock peened Ti6Al4V and Al6061‐T6 alloys

AbstractPropagation of fatigue crack in laser shock peened metallic component is retarded by introduction of deep compressive residual stresses during the process. Apart from large compressive residual stress build‐up near the surface, surface topography is also significantly altered during laser shock peening. However, a systematic evaluation of the individual effects of residual stresses and surface topography as well as their interaction effects on fatigue crack initiation and growth is still lacking. This study investigates the effect of laser shock peening on near‐surface properties of Ti6Al4V and Al6061‐T6 alloys and how these changes dictate their overall fatigue performance. Microstructure, surface topography, hardness and residual stress state of the alloys are investigated before and after peening, and four‐point bending fatigue tests are performed to obtain Wöhler curves (S‐N curves) for each case. The results show that both surface residual stresses and surface topography influence the fatigue life of a component. Compressive residual stresses were induced to a depth beyond 1 mm for both alloys. Fatigue life of Ti6Al4V alloy increased by at least 1.28 times after laser shock peening due to the introduction of deep compressive residual stresses with minimal change in surface topography. By contrast, the improvement is nominal for Al6061‐T6 alloy due to the surface roughening effect introduced by laser peening, which results in early crack initiation and negates the beneficial effect of compressive residual stresses.