Compressive Residual Stress Research Articles

Machining-Induced Surface Integrity Enhancement of Ti-6Al-4V Titanium Alloy via Ultrasonic Vibration Side Milling Under High-Speed Machining and Dry Conditions

Ti-6Al-4V titanium alloy is widely used in aerospace and other fields due to its excellent performance, but conventional machining has problems such as high cutting force, high temperature, and tool wear, which leads to the difficulty of balancing surface quality and efficiency. Ultrasonic vibration-assisted machining can effectively improve machining performance. Although the cutting force and heat of ultrasonic vibration-assisted machining have been researched widely in the past, the selection of process parameters and the mechanism of surface integrity improvement under dry high-speed milling still need to be investigated in depth. In this research, we compare the surface topography, roughness, hardness, and residual stress of conventional milling (CM) and ultrasonic vibration side milling (UVSM) at four cutting speeds (40, 60, 80, and 100 m/min) and two feeds (0.01 and 0.02 mm/z) and reveal the mechanism of improving the surface integrity of Ti-6Al-4V under dry high-speed conditions. The results show that compared to CM, UVSM leads to a reduction in surface roughness, maintains a good surface profile at high feed, increases the residual compressive stress by up to 79%, and increases the surface hardness by 9.88%–14.06%. Its discontinuous cutting characteristics reduce cutting forces and heat accumulations, effectively improving surface integrity. However, higher cutting parameters lead to increased roughness and lower residual compressive stresses, requiring a balance between efficiency and quality. The research results provide process guidance for ultrasonic dry high-speed machining of Ti-6Al-4V, which is important for precision manufacturing.

Effect of Process Parameters on Residual Stresses of Cold Gas Sprayed IN718 Coatings on Large Repair Geometries

Abstract The residual stresses induced by the various process conditions in engineering components can have a significant impact on their structural integrity and performance. It is essential to ensure reliable control of the mechanical properties of structural components during the repair process, as this directly affects their performance and longevity. Cold gas spray, a solid-state deposition technique, involves the high-velocity impact of fine powder particles onto a substrate, resulting in the formation of a dense, metallurgically bonded coating. The aim of this study is to investigate the suitability of cold gas spraying parameters for the repair of large cavities in components made of Inconel 718. Two sets of parameters, approaching the limits of the spraying facility, have been utilized and analyzed using particle diagnostics. Experimental methodologies involve the characterization of residual stress profiles using techniques such as in situ curvature measurement and the incremental hole drilling method after the cold gas spray repair. Additionally, the microstructure and topography of the as-sprayed repair coatings are demonstrated. The results demonstrate the ability of cold gas spray to successfully fill deep repair cavities and adjust the residual stress state of such repair coatings by varying the processing parameters. Lower residual compressive stresses in the layer were achieved by utilizing gas parameters, wherein the particles impact the substrate at an elevated temperature and at a comparatively reduced velocity. Both conditions exhibited coatings with consistent microstructure, good adhesion and uniform topography without major defects. This research demonstrates the potential of cold gas spray as a viable and efficient repair method for large repair geometries, offering a promising avenue for enhancing the reliability and lifespan of critical engineering structures.

Experiments and Multiscale Simulation on Enhancement Mechanism of Zirconium Alloy Microstructure and Properties by Laser Shock Peening

Zirconium alloys are critical materials in nuclear engineering due to their exceptional irradiation resistance and corrosion stability. However, prolonged exposure to extreme operational environments, including a high radiation, mechanical stress, and corrosive media, induces surface degradation mechanisms including stress corrosion cracking and erosion from impurity particle impacts, necessitating advanced surface treatments to improve hardness and corrosion resistance. We explore the application of laser shock peening (LSP) to enhance the surface properties of the Zr4 alloy. Experimental analyses reveal substantial microstructural modifications upon the LSP. The surface grain refinement achieved a maximum reduction of 52.7% in average grain size (from 22.88 to 10.8 μm2), accompanied by an increase of 59% in hardness (204 to 326 HV). Additionally, a compressive residual stress layer (approximately –100 MPa) was generated on the treated surface, which reduces the risk of stress corrosion cracking. To elucidate the mechanistic basis of these improvements, a multiscale computational framework was developed, integrating finite-element models for macroscale stress field evolution and molecular dynamics simulations for nanoscale dislocation dynamics. By incorporating the strain rate as a critical variable, this framework bridges microstructure evolution with macroscopic mechanical enhancements. The simulations not only elucidated the dynamic interplay between shockwave-induced plastic deformation and property improvements but also exhibited a good consistency with experimental residual stress profiles. Notably, we propose the application of strain rate-driven multiscale modeling in LSP research for Zr alloys, providing a predictive method to optimize laser parameters for a tailored surface strengthening. This study not only confirms that LSP is a feasible strategy capable of effectively enhancing the comprehensive surface properties of Zr alloys and extending their service life in nuclear environments, but also provides a reliable simulation methodology in the field of laser surface engineering of alloy materials.

Comparative Study on the Influence of Residual Tensile and Compressive Stresses From Welding on the Fatigue Crack Propagation

Abstract This study aims to compare the influence of residual tensile and compressive stresses resulting from welding on the fatigue crack propagation. The development of fatigue fractures within zones characterized by residual tensile and compressive stresses is investigated using numerical simulations. A quantitative evaluation of the impact of residual stresses on the crack propagation is conducted by comparing the crack opening loads in cases with and without residual stresses. A series of comparative analyses of crack closure parameters is performed to examine the effects of changes in the load level (e.g., load ratio, maximum load, and overload ratio) on the release and redistribution of welding residual stresses. The research findings indicate that the influence coefficients for residual tensile stress and compressive stress on the fatigue crack propagation are 0.65 and 1.5, respectively. Increasing the cyclic loading amplitude and overloading are beneficial for reducing the difference in crack closure parameters between cases with residual stress and those without, weakening the influence of welding residual stress on the crack growth.

A Si3N4–TiB2/SiCN–B4C laminated ceramic tool integrating force measurement function with piezoresistive effect

AbstractIn this study, the Si3N4–TiB2/SiCN–B4C laminated the ceramic tool integrating force measurement function with piezoresistive effect was fabricated. The influence of thickness ratio on the residual thermal stress distribution, the mechanical properties, microstructure and piezoresistivity of the laminated ceramic were investigated. The turning experiment was carried out. The results indicate that the microstructure of laminated ceramic was similar with different thickness ratio. However, the thickness ratio can influence the mechanical properties of laminated ceramics by residual thermal stress. The residual thermal stress, fracture toughness of the laminated ceramic surface initially increase and then decrease with an increasing in thickness ratio. When the thickness ratio was 0.2, the residual compressive stress on the laminated ceramic surface was maximum, and the laminated ceramic exhibit better mechanical properties. The flexural strength, fracture toughness, and Vickers hardness were 405 ± 13 MPa, 8.3 ± 0.12 MPa·m1/2, and 16.8 ± 0.2 GPa. Due to the similar microstructure, the piezoresistivity of laminated materials did not change with the variation of thickness ratio. The average gauge factor of laminated ceramics were around 7900. In addition, the time–resistance curves of the Si3N4–TiB2/SiCN–B4C laminated ceramic tool at cutting depths of 0.2 and 0.4 mm were measured through turning experiments. The measured cutting force curves are consistent with the simulated cutting force curves.

Investigation of Fretting Fatigue Behavior of Shot Peening–Treated Ti‐6Al‐4V Dovetail Joints

ABSTRACTThis study investigates the fretting fatigue behavior of shot peening (SP) on Ti‐6Al‐4V dovetail tenons and slots in a room‐temperature environment. A real‐time crack observation system was developed to facilitate this research. The results show that SP can significantly improve the fretting fatigue life of dovetail specimens, especially the crack initiation life. However, SP treatments on the dovetail tenons can lead to fatigue fracture failures in untreated dovetail slots. Notably, the SP treatment applied to both the dovetail tenon and dovetail slot improved the fretting fatigue life by approximately 600% compared to the untreated specimens. This improvement is primarily attributed to the fact that the SP treatment introduced a certain depth of plastic deformation layer, and the presence of compressive residual stresses inhibited the crack initiation and early propagation rates. In addition, the high roughness friction interface changes the early fretting operation mechanism and stress distribution, thus reducing the stress concentration at the lower edge of the contact zone.

Tailoring strength and ionic conductivity in zirconia‐based solid oxide electrolytes using a multimaterial approach

AbstractA multimaterial approach is explored for tailoring the mechanical and functional properties of zirconia‐based ceramic electrolytes to be employed in electrochemical solid oxide cells (SOCs). The combination of alumina‐toughened zirconia (ATZ) surface layers with an embedded 8 mol% yttria‐stabilized zirconia (8YSZ) core layer introduces compressive residual stress in the electrolyte surface upon cooling from sintering. Biaxial bending is employed to assess the strength distribution in the multimaterial architectures compared to the monolithic counterparts. Electrochemical impedance spectroscopy is used to measure the ionic conductivity of the samples in the temperature range between 600°C and 1000°C. The effect of alumina addition is investigated in samples containing ATZ surface layers with 10 vol% or 20 vol% alumina. Experimental results show that the strength of multimaterial electrolytes can be increased by up to ∼30% compared to the monolithic 8YSZ electrolyte, while holding similar overall ionic conductivity compared to the 8YSZ base material. The approach presented in this work offers new paths to enhance the structural properties of functional ceramics in SOCs, which may also be applied to other systems such as ceramic membranes or ceramic sensors.

Fabrication of Mechanically Robust Hydrophobic Surfaces Using Femtosecond Laser Shock Peening.

The harsh service environment has increased the demand for hydrophobic surfaces with excellent mechanical properties; however, how to manufacture such surfaces remains a significant challenge. In this study, a method for fabricating hydrophobic surfaces with excellent mechanical properties using femtosecond laser shock peening (fs-LSP) is proposed, without the need for any additional processing steps. Taking CH1900A martensitic steel as an example, a systematic analysis of the microstructure was conducted after fs-LSP, revealing the mechanisms by which fs-LSP affects surface morphology, grain structure, dislocation density, and grain boundary characteristics. The high-density dislocations and grain refinement induced by fs-LSP significantly enhanced the surface hardness and introduced residual compressive stresses. Additionally, the laser-induced periodic micro/nanostructures on the surface ensured excellent hydrophobic properties. The effect of single pulse energy and the number of impacts on fs-LSP has also been discussed in detail. As the pulse energy and number of impacts were increased, the surface microstructure of the material was progressively optimized, evidenced by grain refinement, an increase in geometrically necessary dislocation (GND) density, and a higher proportion of high-angle grain boundaries (HAGBs). Such optimization is not monotonous or unlimited; a pulse energy of 75 μJ and six impacts achieved the optimal effect, with the surface hardness reaching up to 8.2 GPa and a contact angle of 135 degrees. The proposed fs-LSP provides a new strategy for manufacturing hydrophobic surfaces with excellent mechanical properties, and the detailed discussion and analysis also provide theoretical guidance for process optimization.

Influence of Gel-Type Confinement for Laser Shock Peening of a Ni-Based Alloy.

Laser shock peening (LSP) significantly enhances fatigue and corrosion resistance, especially in additively manufactured components. This effect is stronger when confinement is used; typically, it is water. However, water poses risks to sensitive electronics. As an alternative, this study explored gel-based confinement. A Ni-based alloy was LSP-treated using 532 nm and 1064 nm wavelengths, with three types of gel compared to water as a control. The results showed that gel confinement can induce compressive residual stresses and increase surface microhardness. However, gels were generally less effective than water in terms of residual stress magnitude and depth of hardening. Additionally, gel confinement required the use of a 1064 nm laser, whereas water confinement was more effective with 532 nm. Among the gels tested, one adhesive variant performed best due to improved surface contact and strong adhesion. The observed increase in microhardness and compressive stress was linked to surface grain refinement and twinning. Overall, adhesive gels offer potential benefits for LSP, particularly for additively manufactured parts, which often have high surface roughness and require non-conductive confinement solutions.

Effect of burnishing strategies on surface integrity, microstructure and corrosion performance of wire arc additively manufactured AZ31 Mg alloy

AZ31 Mg alloy is an emerging material that has received considerable attention in aerospace, automotive, and temporary biodegradable implant applications owing to its attractive properties, such as low density, high specific strength, and biodegradability. Nevertheless, some shortcomings in Mg alloys are their low ductility, which is associated with challenging its manufacturing, and poor corrosion resistance associated with unreliable components. Therefore, a cold metal transfer wire arc additive manufacturing (CMT-WAAM) process is used to manufacture AZ31 Mg alloy and achieved 29.4 % ductility by controlling the gas porosity, keyhole porosity, and internal cracks. Further, severe plastic deformation is induced on the surface of deposited parts by low plasticity burnishing (LPB) with parallel and cross-pattern burnishing to modulate their surface to slow down the kinetics of the corrosion damage. The average surface roughness (Sa) of the cross-burnishing pattern is 0.235 μm, which is 123.6 % lower than the parallel burnished and 261.7 % lower than the milled specimens. The residual stress (RS) of WAAM is 40 MPa with a tensile nature; however, it is drastically reduced and develops compressive RS of 45 MPa under a parallel burnishing pattern and 62 MPa under a cross-burnishing pattern. Moreover, LPB with cross pattern deformed ∼395 μm depth of WAAMed AZ31 workpiece, which is ∼ 45 % higher than deformed depth (∼272 μm) by parallel pattern burnishing. The electrochemical corrosion rate of the WAAM specimen is 9.71 mm/year, and it is reduced to 1.82 mm/year under LPB caused by compressive residual stress and grain refinement.

Effect of compressive residual stress and surface morphology introduced by shot peening on the improvement of fretting fatigue life of TC4

Effect of compressive residual stress and surface morphology introduced by shot peening on the improvement of fretting fatigue life of TC4

Effect of Microstructure and Compressive Residual Stress on the Fatigue Performance of AISI 4140 Steel with QPQ Salt-Bath Nitro-Carburizing.

Quench-polish-quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the outermost part of the QPQ-treated sample. The dense compound layer formed after nitro-carburizing in a salt bath consisted of refined granular Fe3N and transformed to Fe2N after post-oxidation treatment. Micro-shot peening (MSP) was adopted before QPQ treatment to increase the treated steel's fatigue performance. The results indicated that MSP slightly increased the thickness of the compound layer and harden depth, but it had little effect on improving the fatigue strength/life of the QPQ-treated sample (SP-QPQ) compared to the non-peened one (NP-QPQ). A deep compressive residual stress (CRS) field (about 200 μm) and a hard nitrided layer showed a noticeable improvement in the fatigue performance of the QPQ-treated ones relative to the 4140 substrates tempered at 570 °C. The ease of slipping or deforming on the substrate surface was responsible for its poor resistance to fatigue failure. The cracking and spalling of the brittle surface layer were the causes for the fatigue crack initiation and growth of all of the QPQ-treated samples fatigue-loaded at/above 875 MPa. It was noticed that fatigue crack initiation at the subsurface inclusions was more likely to occur in the SP-QPQ sample fatigue-loading at 850 MPa or slightly above the fatigue limit.

Experimental and Numerical Analysis of Compressive Residual Stresses Induced by Shot Peening Treatment for Industrial Applications

Experimental and Numerical Analysis of Compressive Residual Stresses Induced by Shot Peening Treatment for Industrial Applications

Removing Alpha Case from Laser Powder Bed Fusion Components by Cavitation Abrasive Surface Finishing.

Laser powder bed fusion (L-PBF) has become a highly viable method for manufacturing metal structural components for a variety of industries. Despite many attractive qualities, the rough surfaces of L-PBF components often necessitates post-processing treatments to improve the surface finish. Furthermore, heat treatments are generally necessary to control the microstructure and properties of L-PBF components, which can impart a detrimental surface oxide layer that requires removal. In this investigation, cavitation abrasive surface finishing (CASF) was adopted for the surface treatment of Ti6Al4V components produced by L-PBF and removal of the surface oxide layer. The surface texture, residual stress, and material removal were evaluated over a range of treatment conditions and as a function of the target surface orientation. Results showed that CASF reduced the average surface roughness from the as-built condition (Ra ≈ 15 µm) to below 5 µm as well as imparted a surface compressive residual stress of up to 600 MPa. The CASF treatment removed the alpha case from direct line-of-sight surfaces under a range of treatment intensity. However, deep valleys and surfaces at large oblique angles of incidence (≥60°) proved challenging to treat uniformly. Overall, results suggest that CASF could serve as a potent alternative to chemical treatments for post-processing of L-PBF components of titanium and other metals. Further investigation is recommended for improving the process effectiveness and to characterize the fatigue performance of the treated metal.

Stress-induced phase separation in plastics drives the release of amorphous polymer micropollutants into water

Residual stress is an intrinsic property of semicrystalline plastics such as polypropylene and polyethylene. However, there is no fundamental understanding of the role intrinsic residual stress plays in the generation of plastic pollutants that threaten the environment and human health. Here, we show that the processing-induced compressive residual stress typically found in polypropylene and polyethylene plastics forces internal nano and microscale segregation of low molecular weight (MW) amorphous polymer droplets onto the plastic’s surface. Squeeze flow simulations reveal this stress-driven volumetric flow is consistent with that of a Bingham plastic material, with a temperature-dependent threshold yield stress. We confirm that flow is thermally activated and stress dependent, with a reduced energy barrier at higher compressive stresses. Transfer of surface segregated droplets into water generates amorphous polymer micropollutants (APMPs) that are denatured, with structure and composition different from that of traditional polycrystalline microplastics. Studies with water-containing plastic bottles show that the highly compressed bottle neck and mouth regions are predominantly responsible for the release of APMPs. Our findings reveal a stress-induced mechanism of plastic degradation and underscore the need to modify current plastic processing technologies to reduce residual stress levels and suppress phase separation of low MW APMPs in plastics.

Inherent Strain Modelling and Neutron Diffraction Stress Analyses in Invar- 10wt%TiCN Manufactured by Laser Powder Bed Fusion

In this study, the residual stress state of an Invar-10wt%TiCN composite was evaluated through experimental non-destructive neutron diffraction (ND) of the FeNi phase and inherent strain modelling (ISM) simulations. Comparisons were made to the stress state of FeNi in Invar to investigate the degree of change in the alloy due to the addition of the TiCN. The materials were fabricated using laser powder bed fusion (LPBF) according to a full factorial Central Composites Design of Experiments approach to develop the optimal process parameters. High densities of 99.87% for Invar and 99.28% for Invar-10wt%TiCN were achieved, with the TiCN addition leading to a hardness improvement of approximately 71.8%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were done to study the microstructure. The TiCN resulted in a high distortion of 113% in the ISM cantilever sample due to its higher coefficient of thermal expansion. Close agreement was found between the ISM simulation and the ND experimental residual stress results. The stresses are predominantly compressive in the interior and tensile on the surfaces. This agreement enabled extrapolations of the estimated stresses in the near-surface regions. Magnitudes are dependent on the stress component considered and build position. Grain refinement in the Invar-TiCN composite enhanced the compressive residual stresses.

STRENGTHENING Ti-15-3: DISCOVERING THE FATIGUE-BOOSTING WONDERS OF LASER SHOCK PEENING

Laser shock peening (LSP) is a promising surface modification technique used to enhance the surface properties of material. This study investigates the impact of laser shock peening without a protective coating (LPwC) on the fatigue behavior of the duplex-aged (DA) Ti-15-3 alloy with a power density of 9[Formula: see text]GW/cm2 power density and a wavelength of 1064[Formula: see text]nm. The application of laser shock peening without Coating (LPwC) resulted in the development of a titanium oxide layer on the surface of the material, a change that was not seen in the untreated samples and is linked to the high-energy nature of the laser treatment. The untreated DA specimens displayed a compressive residual stress (CRS) of −198 MPa at the surface, which shifted to tensile stress at a depth of 100[Formula: see text][Formula: see text]m. In comparison, the samples subjected to laser peening exhibited a significant increase in CRS, reaching [Formula: see text] MPa at the same depth. Furthermore, the hardness of the surface rose from 350[Formula: see text]HV in the untreated samples to 546[Formula: see text]HV in those that underwent laser peening, emphasizing the work hardening induced by the treatment. Results from axial fatigue testing demonstrated that LPwC markedly improved the fatigue life of the Ti-15-3 alloy, attributed to the combined effects of CRSs, work hardening, and changes in microstructure. These findings highlight the substantial promise of LPwC as a surface treatment method for enhancing the fatigue resistance of DA Ti-15-3 alloy, which is crucial for applications in aerospace and defense. The insights gained can serve as a basis for refining laser peening parameters to further enhance the material’s performance.

In Situ Synchrotron X-Ray Diffraction Analyses of the Low-Pressure Carburizing Process on Steel AISI 5120 Using a Reflection Setup

Abstract Low-pressure carburizing (LPC) is a recipe-controlled heat treatment process for surface layer hardening. The combination of the process parameters determines the chemical gradients established within the case, the local microstructure and the depth distribution of the resulting process-induced residual stresses. Here, the objective was to quantify the influence of the process parameters on the resulting material state of the case hardening steel AISI 5120 (EN 20MnCr5). Therefore, the carburizing and quenching processes were examined using a self-built process chamber specially designed for in situ synchrotron X-ray diffraction experiments. A method for synchrotron X-ray diffraction in reflection geometry was developed to investigate the LPC process. It could be demonstrated that such experiments enable the analysis of microstructural changes, phase transformations and stress evolution at the immediate surface layer with high temporal resolutions. From a material science perspective, the investigations showed, among others, a carbon saturation of the austenite phase within 10 seconds during the boost segments of the LPC process and the formation of compressive residual stresses below -180 MPa after subsequent quenching.

The influence of ultrasonic shot peening on the microstructure and fatigue behavior of TC17 alloy

This research presents a quantitative analysis of TC17 alloy subjected to ultrasonic shot peening (USP) treatment. The effects of USP treatment under different Almen intensities on surface roughness, microstructure, plastic strain range, microhardness, residual stress, fatigue behavior and strain gradient of TC17 alloy were analyzed. Results show that increasing Almen intensity from 0.15 mmA to 0.25 mmA leads to a 27% increase in surface roughness, a 12% increase in surface compressive residual stress value, a 29% increase in the depth of compressive residual stress layer, and a 6.7% increase in the maximum value of compressive residual stress. Microstructural analysis reveals material stacking, pores, and microcracks on the specimen surface and grain refinement characteristics in the surface and subsurface layers. Strain gradient analysis shows that the deformation layer depth is uniformly distributed. An increase in Almen intensity leads to a higher degree of plastic deformation and work hardening, and the increase in compressive residual stress layer depth counteracts early fatigue failure caused by high roughness.

Ultrasonic rolling strengthening theory and mechanism analysis of high-strength 42CrMo steel

42CrMo steel is widely utilized in the manufacturing of high-speed, heavy-duty components due to its excellent wear resistance and hardness. To further enhance its performance and extend its service life, ultrasonic rolling strengthening technology has been employed. However, the underlying microscopic strengthening mechanisms induced by ultrasonic deformation require comprehensive investigation. This study aims to analyze the microscopic strengthening mechanisms of unquenched 42CrMo steel through theoretical modeling, processing experiments, and electron backscatter diffraction (EBSD) microstructure characterization. The research focuses on key aspects such as contact mechanics, residual stress distribution, grain boundaries, orientation evolution, and microtexture development under ultrasonic rolling. Experimental results demonstrate that ultrasonic rolling induces severe plastic deformation on the material’s surface, generating significant residual compressive stress within the workpiece. On a microstructural level, ultrasonic rolling increases grain density, refines grain size, and significantly enhances dislocation density. In addition, the formation of fiber texture and a {110} <441> texture was observed, driven by multi-energy field coupling and the natural rotation of slip planes. Importantly, the high-angle random grain boundaries in the unquenched 42CrMo steel matrix were transformed into low-angle boundaries due to the combined effects of high-frequency vibrations and static pressure, which promoted dislocation slip and redistributed grain orientations. These findings provide an in-depth understanding of the microscopic strengthening mechanisms of ultrasonic rolling, highlighting its potential to achieve precise microstructural control and improve the mechanical performance of 42CrMo steel.