Magnitude Of Compressive Residual Stress Research Articles

Research on the residual stress induced by square-spot laser shock peening on 2024-T351 specimens

Laser peen forming (LPF) is an appealing technique for forming metal sheets using high-energy, short-duration laser pulses. The deformation of the target metal plate is closely related to the magnitude and distribution of laser-induced residual stress. Consequently, the relationship between process parameters and residual stress is worth researching. In this research, two process parameters in LPF, laser energy and coverage ratio (spot distance essentially), and one workpiece parameter, plate thickness, were examined through an element method (FEM) of multiple square-spot laser shock peening (SSLSP). Corresponding experiments of SSLSP on aluminum alloy 2024-T351 test blocks were conducted, together with an X-ray diffraction (XRD) residual stress measurement and a surface morphology observation. The FEM simulation and experimental results show that congested laser spots had a significant influence on the magnitude of compressive residual stress; higher laser energy was beneficial to the depth of the compressive stress layer but could decrease its magnitude. Therefore, for better forming ability, higher laser energy and a higher coverage ratio are beneficial; for surface strengthening, laser energy should not be too large, and the coverage ratio should be larger than 100% to ensure that the residual stress on the treated surface is compressive, resulting in better surface integrity.

Numerical simulation study of combined shot peening and laser shock peening on surface integrity of Ti-6Al-4V titanium alloy

Combined shot peening and laser shock peening (CSP) can introduce high surface compressive residual stress (CRS) and deep CRS layer, and reduce the high surface roughness caused by shot peening. The relationship between CSP sequences and surface integrity, including CRS and surface roughness, is far from satisfying the actual demand. In this paper, we construct a finite element model considering initial surface profile features. The experimental results agree with the simulated results. Based on the simulation results, axial and longitudinal stress wave transfer effects on surface CRS and depth CRS are investigated. Compared with shot peening (SP) and laser shock peening (LSP) alone, CSP treatment can increase CRS depth and CRS magnitude by 1060 μm and 50 ∼ 80Mpa, respectively. In addition, the roughness following CSP treatment is lower than that observed after SP treatment alone, and the roughness varies depending on the sequence of CSP treatment. Specifically, the roughness values for SP, SP + LSP, and LSP + SP are 0.938 ± 0.031 μm, 0.982 ± 0.11 μm, and 1.168 ± 0.093 μm, respectively. The surface morphology, hardness, and simulation results are combined to reveal the reasons for the reduction of surface roughness after CSP treatment. The changes of peaks and valleys after CSP treatment compared with single SP treatment were studied, and the variation trend of surface roughness was further explained.

Finite-element simulation of residual stresses induced by laser shock peening in TC4 samples structurally similar to a turbine blade

This study is devoted to the investigation of residual stresses distribution (RSD) in a TC4 sample treated with laser shock peening. The study placed special emphasis on analyzing the RSD at the part of the samples structurally similar to a turbine blade, which is more frequently subjected to damage during service according to the aircraft statistics. Results of simulation showed that low power density of 1.11 GWt/cm2 could not induce compressive residual stress on the surface of a treated object. Furthermore, increasing the overlapping of laser spots does not improve the situation and still fail to induce surface compressive residual stress at a laser intensity of 1.11 GWt/cm2. The compressive stresses occur only with the rise in power density. Reducing the spot size from 3 mm to 1 mm for the power density of 10 GWt/cm2 results in a 20% increase in the magnitude of compressive residual stress in the area of interest. Moreover, applying 35% overlapping further enhances this value. In addition to increasing the magnitude of residual stress, this approach also leads to a more homogeneous RSD of the treated material.

An Investigation on Laser shot peened surfaces

The present work is focused on the influence of zinc trivalent plating on laser shot peened AISI 304 stainless steel samples to improve the corrosion resistance of the steel surface. AISI 304 steel samples were heat treated by annealing and polished to perform Laser Shot Peening (LSP) process using Nd-YAG laser functioning at a pulse interval of 10ns with different energies of 200 mJ, 300 mJ and 400 mJ on each sample. The highest magnitude of compressive residual stresses is induced using the pulse density of 2500 pulses/cm2. The laser treated sample was characterized by surface hardness using Vickers micro hardness test and surface morphology using an optical microscope and SEM analysis. The surface hardness of the sample is increased by increasing laser energy. The prepared zinc trivalent is plated using electro deposition on the laser treated surface by maintaining current between 1.5 to 4 amps/Dm2, and temperature between 20 to 40 deg C. MAHR’s roughness tests were performed to find the surface roughness of the sample. The surface roughness has drastically increased on zinc coated samples compared to samples without coating. The Vickers micro hardness test conducted on zinc trivalent plated sample revealed the increase in hardness value of 200mJ by 24% compared with 200mJ sample without coating. SEM and EDAX were carried out to know the changes occurred in the chemical composition of the samples before and after coating.

Effects of microstructure and inherent stress on residual stress induced during powder bed fusion with roller burnishing

A hybrid metal-additive manufacturing (AM) process that combines laser-based powder bed fusion (PBF-LB) with interlayer burnishing is investigated using a comprehensive modeling framework to provide new insights into how the inhomogeneous microstructure and residual stress from the laser powder bed fusion process affect the induced residual stress field that evolves during interlayer burnishing. Researchers have recently studied changes in microstructure resulting from similar hybrid metal-additive processes, however, it was only hypothesized that the resulting microstructure has some influence on the induced residual stress. In addition, researchers have numerically investigated the influence of burnishing/rolling process parameters on induced stress but neglected the effects of microstructure, thereby making homogeneous, isotropic assumptions. Such practice inhibits the prediction of microstructure-driven anisotropy that can exist in the inhomogeneous fused layer. This paper parametrically examines the influence of microstructure modeling, inherent residual stress mapping, and environment temperature on the induced residual stress during the hybrid metal-additive process. The demonstrated modeling framework incorporates inherent residual stresses that emerge from the laser powder bed fusion process, as well as the predicted microstructure, in a subsequent burnishing simulation to elucidate their individual and combined influences on the burnishing-induced residual stress. Findings reveal that modeling an inhomogeneous PBF-LB microstructure introduces an anisotropic distribution of plastic strain and residual stress along the burnished surface; a periodicity in planar stress components along the treated surface coincides with the PBF-LB scan lines. Effects of inherent residual stress on the burnishing-induced residual stress is less significant, but nonetheless observable. Elevated temperatures not only reduce the magnitude of compressive residual stress induced but also result in less variation of residual stress component magnitudes predicted along scan lines and hatch spaces. The presented framework offers new insights into the decoupled influences of microstructure and PBF-LB residual stress on burnishing-induced stresses that are not distinguishable via experimental techniques. However, trends in averaged residual stress through the depth of the specimen, as well as surface hardness magnitudes after burnishing show good agreements, respectively, with X-ray diffraction and microindentation measurements documented in the literature.

Crystallographic orientation and wear characteristics of TiN, SiC, Nb embedded Al7075 composite

A wear resistant TiN, SiC, Nb blended Al7075 composite was fabricated by ultrasonic assisted squeeze casting route. The X-ray residual stress analysis probed that the fabricated component had shown high magnitude of compressive residual stresses induced in the range of 279 ± 8 MPa. Further the inverse pole figure generated by Electron Backscattered Diffraction (EBSD) delineated the occurrence of grain refinement caused by potential heterogenous nucleants TiN and Nb. As an effect of grain refinement, pronounced improvement in microhardness was observed. The results of dry sliding wear analysis of the fabricated component had shown a superior wear resistance by exhibiting low friction coefficient (LFC) of 0.19. It was found that the segregated reinforcements across the grain boundaries yield positive effects on improving the tribological performance by Zenner pinning mechanism and Orowan load bearing effect. Thus, easy sliding was facilitated by attenuating the impact of contact stresses between the intender and counterpart interface.

Surface generation in high-speed grinding of brittle and tough ceramics

Grinding induced sub-surface defects substantially impair the functionality of ceramic components. Effective control of such defects is possible through identification and understanding the governing factors. The present work investigates the interaction of abrasive grits over the ground surface to identify the governing factors for effective control of such defects during high-speed grinding of a brittle (alumina) and a tough (yttria-stabilized zirconia (YSZ)) ceramic. High-speed grinding was carried out using single-layer electroplated diamond grinding wheels in the speed range of 40–200 m/s. The important grinding characteristics, such as material removal mode, residual stress, surface roughness, etc., were correlated with the maximum uncut chip thickness (hm) and the scallop height (Sg). The hm represents the interaction of active grits at the exit of the grinding zone, whereas the interaction of active grits while entering the grinding zone (at ground surface) leads to the formation of scallops. Instead of hm, material removal mode and other related grinding characteristics are found to be governed by the Sg. An efficient reduction of approximately 90 % in Sg is realized by increasing the grinding speed from 40 m/s to 200 m/s. For a brittle ceramic like alumina, such a drastic reduction in Sg reduced grinding induced defects by more than 75 %. For a tougher ceramic like YSZ, a reduction of more than 30 % in the magnitude of compressive residual stress is observed with a reduction in Sg at a higher grinding speed of 200 m/s. This study manifests Sg as a predominant factor in governing the ground surface characteristics during ceramic grinding, which can be effectively utilized to control grinding induced defects in ground ceramic parts.

Improving the fatigue performance of vanadium and silicon alloyed medium carbon steels after nitriding through increased core fatigue strength and compressive residual stress

The fatigue performance of nitrided medium carbon steels, alloyed with V and Si, and heat treated to form martensite and bainite microstructures, was evaluated using cantilever bending fatigue testing. Hardness testing and X-ray diffraction residual stress measurements were used in conjunction with an analysis of the applied stress distributions to determine vulnerable regions of crack initiation. The analysis was correlated with experimental scanning electron microscopy observations of crack initiation location. Increases in V and Si content lead to higher core hardness and higher core fatigue strength which increase the applied stress needed to initiate fatigue failure originating subsurface below the case. Increases in V and Si content also increase the magnitude of compressive residual stress, which increases the applied stress needed for surface initiated failure. The combination of increased core fatigue strength and magnitude of compressive residual stress improve the fatigue performance after nitriding compared to other nitrided medium carbon steels reported in literature.

Part deflection and residual stresses in laser powder bed fusion of H13 tool steel

This study aims at a comprehensive investigation of residual stresses in laser powder bed fusion processed H13 tool steel through experiment and part-level simulation. Twin-cantilever beams and cubic coupons were printed in a wide range of process parameters to characterize residual stresses under preheated and non-preheated conditions. Results revealed the significant role of martensitic phase transformation, process parameters, densification level, and preheating condition on the residual stress regime and beam deflections. The residual stress regime was governed by the competition between the tensile and compressive stresses caused by the solidification/cooling contraction and martensitic phase transformation, respectively. The compressive residual stresses on the top surface turned into tensile immediately below the last consolidated layer. Higher heat inputs led to the increased magnitude of compressive residual stresses on the top surface of non-preheated samples. For parts having relative densities higher than 97%, the residual stresses were found to be independent of the densification level. Deflection modeling results indicated that for steels experiencing martensitic phase transformation, the martensite start temperature needs to be set as the relaxation temperature to accurately predict the beam deflection. This study proves that 200 °C of preheating eliminates not only cracks but also the need for stress-relief post-processing.

Additive manufacturing of high-strength alumina through a multi-material approach

This work demonstrates the use of additive manufacturing to design and fabricate alumina ceramics with strength as high as 1 ​GPa. A multi-material approach is employed by embedding alumina-zirconia layers between outer pure alumina layers with significant compressive residual stresses. Biaxial bending is performed both on the 3D printed multi-material and monolithic alumina parts. Results are analysed in the framework of Weibull statistics. A characteristic biaxial strength higher than 1 ​GPa is measured on the multilayers, compared to 650 ​MPa in monolithic alumina, the difference corresponding to the magnitude of compressive residual stresses due to the thermal mismatch between material regions during cooling from sintering. This is the first report of employing additive manufacturing to tailor the strength of alumina ceramics, taking advantage of the layer-by-layer printing process. Designing complex-shaped ceramic architectures with residual stresses through additive manufacturing opens a new path for fabrication of technical ceramics with tailored mechanical properties.

Mechanical and Thermal Load Effects of Novel MWFs Delivery Method in Milling of Ti–6Al–4V

This work mainly focuses on the effectiveness of both rake and flank face application of the different metal working fluid (MWF) strategies such as liquid CO2, minimal quantity lubrication (MQL), and emulsion in face milling of Ti–6Al–4V alloy. Modified CoroMill 600 cutter via internal channels to both rake and flank faces of the inserts with PVD coated inserts were used for the studies. This novel approach of delivery of MWFs has been investigated on effective thermo-mechanical loads; in terms of the evolution of cutting temperature, cutting forces, and residual stresses. The hardness of the machined surfaces and chip microstructure analysis were also conducted to understand more about the mechanical and thermal load effects in machined material and observed parameters. It has been found that the effectiveness of both rake and flank application of the liquid CO2 machining is a better alternative for the emulsion and MQL strategies. Low thermal deformation of the material, higher magnitude of compressive residual stresses, and lower thermal load throughout the machining cycle have been observed. However, an increase in the mechanical load was observed because of the cold strength hardening of the Ti–6Al–4V workpiece at the liquid CO2 environment. These effects are negligible at room temperature after machining. Overall results show that the cryogenic machining offers best and lower thermal load effects over MQL and emulsion strategies for both rake and flank applications.

Design of a disk-mandrel assembly for achieving rotational autofrettage in the disk

Rotational autofrettage is a recently proposed method to induce beneficial residual stresses in axisymmetric hollow cylindrical bodies. The feasibility of the process has been studied for both disks and cylinders used in many engineering applications. The earlier analyses of rotational autofrettage of disks are based on certain assumptions. One of the crucial assumptions is the free rotation of the disk. However, the free rotation of the disk is practically difficult. In practice, it is feasible to rotate the disk by shrink-fitting it over a solid cylindrical mandrel. In view of this, a design of a disk-mandrel assembly for achieving rotational autofrettage in disks is proposed in this article. The main aim of the design is to obtain appropriate values of the disk-mandrel interference and the rotational speed of the assembly to prevent the loss of contact of the disk with the mandrel during rotation. The critical speeds corresponding to the yield onset, contact separation and the full plastic deformation of the disk are obtained as a function of shrink interference. The safe operating design parameters can be decided by plotting the critical speeds with varying interference values. A detailed stress analysis during elastic-plastic loading of the assembly followed by the analysis of residual stresses in the assembly after unloading is presented. The analysis is based on the plane stress assumption, Tresca yield criterion and elastic unloading. The analysis is validated with a finite element method model in ABAQUS. The proposed design is illustrated through the numerical example of an ASTM A723 disk-mandrel assembly to achieve rotational autofrettage in the disk. With a small overstrain level of 17.5% in the disk, a large magnitude of compressive residual stress, viz., 0.52 times the yield stress, is induced.

Effects of in-situ TiB2 particles on machinability and surface integrity in milling of TiB2/2024 and TiB2/7075 Al composites

In-situ ceramics particle reinforced aluminum matrix composites are favored in the aerospace industry due to excellent properties. However, the hard ceramic particles as the reinforcement phase bring challenges to machining. To study the effect of in-situ TiB2 particles on machinability and surface integrity of TiB2/2024 composite and TiB2/7075 composite, milling experiments were performed, and compared with conventional 2024 and 7075 aluminum alloys. In-situ TiB2 particles clustered at the grain boundaries and dispersed inside the matrix alloy grains hinder the dislocation movement of the matrix alloy. Therefore, the milling force and temperature of the composites are higher than those of the aluminum alloys due to the increase of the strength and the decrease of the plasticity. In the milling of composites, abrasive wear is the main wear form of carbide tools, due to the scratching of hard nano-TiB2 particles. The composites containing in-situ TiB2 particles have machining defects such as smearing, micro-scratches, micro-pits and tail on the machined surface. However, in-situ TiB2 particles impede the plastic deformation of the composites, which greatly reduces cutting edge marks on the machined surface. Therefore, under the same milling parameters, the surface roughness of TiB2/2024 composite and TiB2/7075 composite is much less than that of 2024 and 7075 aluminum alloy respectively. Under the milling conditions of this experiment, the machined subsurface has no metamorphic layer, and the microhardness of the machined surface is almost the same as that of the material. Besides, compared with 2024 and 7075 aluminum alloy, machined surfaces of TiB2/2024 composite and TiB2/7075 composite both show tensile residual stress or low magnitude of compressive residual stress.

Laser peening of 420 martensitic stainless steel using ultrashort laser pulses

Abstract Laser shock peening is an established method used to increase resistance of a surface to cracking and fatigue damage by inducing deep compressive residual stresses. Most of the current laser shock peening system utilizes a nanosecond pulse laser with very slow repetition rate (about 5-10 Hz), high pulse energy and a confining medium to constrain the plasma. On the other hand, ultrashort pulse lasers generally have a higher peak power density and operate at higher repetition rate than nanosecond pulse laser. Therefore, there is an opportunity to employ ultrashort pulse lasers to peen the surface in a fast and efficient way. However, limited studies have been performed to investigate the peening capability of ultrashort laser pulses. In this study, femtosecond (fs) pulse laser is used to peen a 420 martensitic steel surface under different coverage. The results show that fs laser can induce peening effect; however, peened depths are much smaller (around 20-30 μm) compared to high energy nanosecond pulse laser peening (up to 1 mm). A maximum compressive stresses of about -80 MPa was recorded at 981% coverage. Increase in coverage produced stress relaxation and did not increase the depth of influence. It was found that the state of the residual stresses depends on four main factors – intensity of ablation-induced shock wave, thermal effect of laser beam, phase transformation of the steel and surface mechanisms such as presence of nano-ripples and oxidation. Further experiments are ongoing to achieve higher magnitude of compressive residual stresses and higher depth of influence.

Effect of single tensile overload on fatigue crack growth behavior based on plastically dissipated energy and critical distance theory

The paper systematically investigates the fatigue crack growth (FCG) behavior of Q345 steel under a single tensile overload during constant amplitude cyclic loadings by combining the experimental, numerical and theoretical methods. Compact tension specimens are applied to explore the retardation effect of FCG rate after the overload application. A predictive technique based on plastically dissipated energy method, critical distance theory and node-release technology is developed to characterize the FCG behavior following the overload. Crack opening displacement and crack opening load level along the crack flank are obtained to explore the effect of overload on plasticity-induced crack closure. Additionally, the stress-strain response at critical distance and compressive residual stress field ahead of crack-tip are further explored to reveal the intrinsic mechanism and accumulative damage. Results show that the magnitude of residual stretched material wedge and value of maximal crack opening load level increase obviously with the increasing of overload; discontinuous closure takes place behind and before plastic wedge at overload location, which limits the stress/strain ranges at crack-tip and thereby retards crack growth. The magnitude of compressive residual stress and size of stress field ahead of crack-tip increase with increasing overload ratio, which aggravates the retardation effect after overload.

Effect of cryogenic cooling on texture and microstructural evolution of ZK60 magnesium alloy during machining

Producing ultra-fine grains on a material’s surface is highly pronounced nowadays, which has more influence on the surface integrity properties of the finished component. In this report, severe plastic deformation (SPD) was employed through cryogenic machining to form fine grains on the machined surface of the ZK60 magnesium alloy. Using liquid nitrogen (LN2) as a coolant during machining of ZK60 alloy induced deformation twins in the grains located on the deformation bands due to severe plastic deformation. Nucleation for the fine grain formation occurred at the deformation shear bands. Evolution of strong basal texture with deformation twins during cryogenic machining increased the fraction of submicron grains from <8% to ≈36%. The average diameter of fine grains was measured as ≈1.2 μm on the machined surface. Moreover, high lattice strain ensured the slip system that necessary for the occurrence of low temperature dynamic recrystallization (DRX). Pole figures resulted from EBSD analysis showed that the refined grains were oriented on the basal plane. The transformation of low angle grain boundaries (LAGB) to high angle grain boundaries (HAGB) about ≈61% under cryogenic machining which was ≈29% in as-received material confirmed the occurrence of grain refinement. Higher magnitude of compressive residual stress was also noticed below the machined surface under cryogenic machining.

Optimization of residual stress field in ultrasonic assisted burnishing process

Surface compressive residual stress and its penetration depth are of important characteristics of burnishing process. The higher values compressive residual stress in the surface of the treated sample can delay the fatigue crack initiation; also, the further penetration depth restricts fatigue crack propagation. However, achieving both of performance at same time needs careful selection of burnishing parameter. In the present study an optimization approach is made to maximize the value of surface compressive residual stress subjected to specified penetration depth. The analytical model of residual stress previously developed by the author is firstly modified with a cubic interval function and then used to find how the ultrasonic assisted burnishing factors i.e. static force, vibration amplitude, ball diameter and material influence the residual stress field distribution. Then the model was then incorporated with particle swarm optimization algorithm to find optimal parameter setting. Results showed that it isn't possible to maximize both the surface compressive residual stress and its penetration depth at same time. Furthermore, to have maximum value of compressive residual stress magnitude at the surface with the penetration depth of 0.5 mm, it is required to use tungsten carbide ball with 3 mm diameter; also, the static load and vibration amplitude should be selected at the values of 120 N and 14 μm. The compressive surface residual stress in optimized condition is about 110 MPa that is compatible well with the 98 MPa obtained by confirmatory experiment. Also, the maximum depth compressive residual stress for optimum condition measured by experiment is 0.7 mm while it is predicted 0.8 mm by analytical approach.

Microstructure-mechanical property correlation in shot peened and vibro-peened Ni-based superalloy

In this experimental research, shot peening (SP) and vibro-peening (VP) processes were employed to modify the surface and sub-surface of a Ni-based superalloy Udimet®720Li. The effect of these treatments on the surface topography, microstructure evolution, and mechanical properties was investigated using instrumented tests. The compressive residual stresses and plastic strain generated through surface treatment were characterized using X-ray diffraction (XRD). The depth of plastically strained region was estimated using a quantitative analysis of grain orientation spread (GOS) data from electron back-scattered diffraction (EBSD) technique. It was observed that the magnitude of compressive residual stresses induced by VP is relatively low compared to SP, but the converse is true for depth of influence (DOI) for the same peening intensity. After thermal exposure at 650 °C (∼0.4Tm) for 5 h, the relaxation of compressive residual stresses and plastic strain was less pronounced in vibro-peening when compared to shot peening representing an improved thermal stability of the former process. Furthermore, 5.24 GPa surface micro-hardness of the untreated sample (O) was increased by ∼30% and ∼25.2% following SP and VP respectively. This resultant micro-hardness enhancement is due to grain refinement, plastic strain effects, and the introduction of low angle grain boundaries (LAGBs). Finally, a positive correlation among microstructural features and mechanical properties was fitted from the experimental data.

Effect of ultrasonic nanocrystal surface modification on elevated temperature residual stress, microstructure, and fatigue behavior of ATI 718Plus alloy

Ultrasonic Nanocrystal Surface Modification (UNSM) is a mechanical surface treatment that induces large compressive residual stresses and near-surface microstructural changes in the material by using repetitive impacts at ultrasonic frequencies with a WC tip. In this study, we investigate the use of UNSM to improve the fatigue life of ATI 718 Plus (718Plus) at high temperature of 650 °C. UNSM induced severe surface plastic deformation which led to nano-sized crystallites, twins, and high dislocation density in the near surface regions, coupled with an increase in surface hardness and high magnitude of compressive residual stresses. This change in the near-surface microstructure remained stable at elevated temperatures. In addition, UNSM retained ∼−680 MPa near-surface residual stress (56% of its initial residual stress) even after 140 h exposure to 650 °C. The retained near-surface residual stresses and the stable microstructure from the UNSM increased the yield strength by ∼11% (∼105 MPa) and endurance limit by ∼8% (∼70 MPa) in corresponding tests at 650 °C. This improvement in fatigue life was attributed to near-surface microstructure changes, material hardening and high compressive residual stress induced by UNSM. The estimated crack growth rates were ∼60% lower for UNSM-treated 718Plus as compared with untreated material. The thermal-mechanical residual stress relaxation indicates the effectiveness of UNSM in improving the fatigue life of 718Plus at 650 °C.

Effect of Ultrasonic Nanocrystal Surface Modification on residual stress, microstructure and fatigue behavior of ATI 718Plus alloy

Ultrasonic Nanocrystal Surface Modification (UNSM) is a mechanical surface treatment that induces large compressive residual stresses and near-surface microstructural changes in the material using repetitive impacts at ultrasonic frequencies with a WC tip. In this study, we investigate the use of UNSM to improve the fatigue life of ATI 718 Plus (718Plus). UNSM induced severe surface plastic deformation in 718Plus, which led to nano-sized crystallites, twins, and high dislocation density in the near surface regions, coupled with an increase in surface hardness by 2.3GPa and high magnitude of compressive residual stresses. These changes increased the endurance limit by ~ 13% (~ 100MPa) in room temperature fatigue tests. This improvement in fatigue life was attributed to near-surface microstructural changes, material hardening and high compressive residual stress induced by UNSM. The crack propagation rates were 66% lower for UNSM-treated 718Plus as compared with untreated material. The residual stress relaxation after cyclic loading indicates the effectiveness of UNSM in improving the fatigue life of 718Plus.