Ultrasonic Nanocrystal Surface Modification Research Articles

Effects of ultrasonic nanocrystal surface modification treatment and subsequent annealing on the microstructure and mechanical properties of rolled AZ31 alloy

Effects of ultrasonic nanocrystal surface modification treatment and subsequent annealing on the microstructure and mechanical properties of rolled AZ31 alloy

Application of impact-based and laser-based surface severe plastic deformation methods on additively manufactured 316L: Microstructure, tensile and fatigue behaviors

Applying post-processing methods can play a crucial role in addressing defects inherent in the as-built state of additively manufactured materials. This study comprehensively examined the effects of various post-processing techniques, including surface severe plastic deformation (SSPD) methods such as severe shot peening (SSP), ultrasonic shot peening (USP), ultrasonic nanocrystal surface modification (UNSM), and laser shock peening (LSP), combined with stress relieving (SR) on the tensile properties and fatigue behavior of laser powder bed fusion (LB-PBF) stainless steel AISI 316L specimens. Experimental characterization was carried out, focusing on microstructure, porosity, surface texture, hardness, residual stresses, monotonic tensile properties, and rotating bending fatigue behavior. The results demonstrated an excellent combination of enhanced strength and ductility after applying SR and SSPD treatments. Additionally, the post-processing methods significantly improved fatigue behavior by increasing strength, closing subsurface pores, surface layer nanocrystallization and hardening, inducing compressive residual stresses, and modifying the surface texture. Notably, in the high-cycle fatigue regime at the lowest stress amplitude, the SR + UNSM treated specimens exhibited the greatest improvement in fatigue life, followed by SR + USP, SR + SSP, SR + LSP, and SR, when compared to the as-built state.

Enhancing high-temperature wear resistance of cladded Inconel 718 through hybrid of directed energy deposition with ultrasonic nano-crystal surface modification

We present an innovative method for achieving highly durable and finely controllable internal microstructures within cladded 718 layers utilizing a hybrid cladding approach. This process alternates between two methods: laser directed energy deposition in which four layers of Inconel 718 built up using a laser power of 350 W and a scanning speed of 800 mm/min, and ultrasonic nanocrystal surface modification (UNSM), applied to every fourth deposited surface at elevated temperatures of 300 and 600 °C, with a frequency of 20 kHz and an interval of 0.05 mm, respectively. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) are used to analyze the effect of grain refinement and concentrated dislocation distribution induced by the hybrid cladding. Through the employment of high temperature UNSM treatment between the cladded Inconel 718 layers, profound grain refinement and dislocation enhancement occur, significantly bolstering the wear resistance of the intermediate layer under high temperature conditions. We conducted thorough analyses, employing finite element analysis and experiments, to investigate the diverse temperature conditions of UNSM treatment and their impact on increasing the affected depth of UNSM treatment. Furthermore, we closely examined the changes in microstructure and mechanical properties within the remelted and UNSM-treated zone of the internal layers. Our study confirms that the high temperature hybrid cladding process, operating below 600 °C, resulted in a 27 % reduction in overall material wear-loss compared to conventional cladding methods. Notably, even in high temperature wear tests ranging from 200 to 800 °C, the proposed method significantly mitigated wear amounts in each case, indicating its potential to enhance the mechanical integrity of various components operating under elevated temperature conditions.

Variations of VHCF Characteristics by Microstructure of a Spring Steel to UNSM Treatment

<i>The bainitic structure resulting from the austempering of spring steel exhibits high strength and ductility. On the other hand, there appears to be no study on the effects of very high cycle fatigue (VHCF) and ultrasonic nanocrystal surface modification (UNSM) of this bainite structure. Therefore, this study compared the fatigue properties of VHCF using spring steel with bainitic and martensitic structures and bearing steel data. This study analyzed the characteristics of microstructure transformation associated with the heat treatment cycles and studied and evaluated the fatigue strength characteristics because of the UNSM in terms of fracture mechanics method and fracture surface analysis through electron backscatter diffraction, scanning electron microscopy fracture analysis, and energy-dispersive spectroscopy analysis. The fatigue limit of UNSM-treated spring steel was improved significantly by approximately 33% to 50% compared to the fatigue test results of the untreated material in the VHCF. In the long life range of bainized spring steel, fish-eye cracks appear in the form of the fine granular area, and fatigue cracks occur in the form of fish-eye cracks that occur in the bainite facet and matrix, resulting in a significant increase in fatigue strength and fatigue life.</i>

Effects of Ultrasonic Nanocrystal Surface Modification on Surface Hardening Mechanism and Wear Behavior of Additively Manufactured High-Manganese Steel

Effects of Ultrasonic Nanocrystal Surface Modification on Surface Hardening Mechanism and Wear Behavior of Additively Manufactured High-Manganese Steel

Microstructural transformation and corrosion–cavitation behavior of ultrasonic nanocrystal surface modified nickel aluminum bronze (NAB)

In this study, nickel–aluminum bronze (NAB) is optimized by ultrasonic nanocrystal surface modification (UNSM), and its surface microstructural evolution, surface hardness, electrochemical corrosion behavior, and cavitation erosion behavior are investigated. The potentiodynamic polarization curves and electrochemical impedance spectra before and after UNSM treatment of NAB are measured using a typical three-electrode system. The cavitation erosion process is simulated through the vibration of ultrasonic waves underwater, and the cavitation erosion resistance performance of various specimens is evaluated. UNSM significantly refines the coarse and heterogeneous multi-phase structure of the cast NAB, providing a relatively uniform and dispersed structure. Simultaneously, severe plastic deformation rapidly increases micro-strains on the NAB surface, which effectively improves its surface hardness from 211 to 360 Hv. After UNSM treatment, the corrosion potential increases slightly; and the passivation potential and current decrease considerably, dropping from 207 to 103 mV and from 5.23 to 2.41 mA/cm2, respectively. This is primarily because of the slowdown of selective-phase corrosion and the uniform formation of an oxide film. Additionally, UNSM parameters affect corrosion potential by regulating surface roughness. A smoother surface corresponds to a higher corrosion potential at the same load. UNSM treatment significantly improves the cavitation corrosion resistance of NAB, primarily because an increase in hardness and uniform distribution of structure effectively slows the speed of crack formation and propagation, which is a result of the synergistic improvement of mechanical and corrosion resistance properties.

Surface heterostructuring of 316L stainless steel manufactured by laser powder bed fusion and hot isostatic pressing

Metal additive manufacturing (AM), offering high freedom of design, has garnered attention as a cutting-edge manufacturing technology. Commonly, hot isostatic pressing (HIP), as post-processing, is utilized to remove undesirable defects in AM parts to obtain fully dense components. However, excessive heating during HIP can result in the deterioration of mechanical properties, limiting their potential for structural industry applications. Herein, we propose a new strategy to obtain an optimized gradient structure to achieve a substantial synergistic effect through ultrasonic nanocrystal surface modification (UNSM) on the HIP-processed AM substrate. The resulting microstructure shows an extended gradient layer reaching the center of the substrate with significant mechanical incompatibility between adjacent domains, showing an excellent combination of strength and ductility. Our study suggests that the optimized gradient structure with superior mechanical properties can be achieved by strategically exploiting HIP-induced effects, which are generally avoided in structural materials due to their deleterious effect on strength.

Magnetic-assisted ultrasonic nanocrystal surface modification induced microstructures of titanium alloy

Surface nanocrystallization together with compressive residual stresses can significantly improve the mechanical properties of metallic materials. An innovative surface process called magnetic-assisted ultrasonic nanocrystal surface modification (MA-UNSM) is reported here. By coupling integrates magnetoplasticity and shocking-induced plasticity, the MA-UNSM can enhance the plastic deformation capability of materials without significantly increasing the USNM processing temperature, thus realizing more effective grain refinement, deeper plastic-affected depth and higher-magnitude residual stresses, as evidenced by microscopic characterization and mechanical measurements. Our results demonstrated that the magnetic field improves the plasticity of the material by reducing the resistance between dislocations and pinning obstacles and thus enhances the effectiveness of ultrasonic peening treatment. Magnetic field with two intensities (0.25 T and 0.6 T) were used to assist UNSM, and the results showed that 0.6 T was the better condition.

Effect of Ultrasonic Nanocrystal Surface Modification to Improve Anti-adhesion to Aluminum for Heat-treated SKD11

Effect of Ultrasonic Nanocrystal Surface Modification to Improve Anti-adhesion to Aluminum for Heat-treated SKD11

Chloride-induced stress corrosion cracking in Austenitic steels for SNF storage canisters - Recent understanding and advances in mitigation and repair

Chloride-induced stress corrosion cracking (CISCC) is a critical threat to stainless steel (SS) spent nuclear fuel (SNF) and radioactive materials storage canisters currently in service worldwide. In the past decade, extensive research has been conducted to understand fundamental mechanisms of CISCC, as well as to develop effective repair and mitigation methods to prevent catastrophic failure of the SNF canisters from CISCC. This review article aims to: (1) summarize recent progress from fundamental studies of CISCC in SS, and (2) present state-of-the-art developments in CISCC mitigation and repair techniques that may be especially well-suited for SNF storage applications, including cold spray (CS), friction stir welding (FSW), friction surfacing (FS), laser shock peening (LSP), and ultrasonic nanocrystal surface modification (UNSM). Knowledge gaps in current understanding of CISCC and roadmaps for deployment of the repair techniques are also discussed.

A comprehensive study on the effects of surface post-processing on fatigue performance of additively manufactured AlSi10Mg: An augmented machine learning perspective on experimental observations

In this study, the efficacy of 21 distinct surface post-processing methods on the fatigue behavior of an additively manufactured (AM) material was investigated. Various treatments, encompassing single-step processes like sand blasting (SB), conventional shot peening (CSP), severe shot peening (SSP), gradient severe shot peening (GSSP), ultrasonic shot peening (USP), severe vibratory peening (SVP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP), laser polishing (LP), tumble finishing (TF), chemical polishing (CP), electro-chemical polishing (ECP), and machining (M), as well as hybrid treatments, were systematically investigated for their impact on the fatigue behavior of hourglass laser powder based fused (LB-PBF) AlSi10Mg specimens. A comprehensive series of experimental tests were carried out, covering surface texture analyses, microstructural characterizations, porosity measurements, hardness, residual stresses (RS), monotonic tensile tests, and rotating bending fatigue tests at four stress levels. Following the experimental investigations, the acquired data were leveraged to develop a machine learning (ML)-based model to correlate the fatigue life with the influencing factors and conduct parametric and sensitivity analyses. The model utilized a deep learning approach to predict the fatigue response of LB-PBF AlSi10Mg, incorporating various artificial neural networks (ANNs) and considering input parameters such as yield strength, ultimate tensile strength, elongation to fracture, porosity, depth of pore closure, surface hardness, depth of hardness variation, surface RS, maximum compressive residual stresses (CRS), depth of the CRS field, top surface grain size, surface layer mean grain size, surface roughness, and stress amplitude. Depending on the life regime, the factors influencing fatigue behavior can vary significantly. In higher stresses, dominated by plastic strains, surface residual stress emerges as the primary factor. Conversely, in lower stresses, dominated by elastic strains, the significance of surface roughness becomes more pronounced, followed by surface residual stress, surface hardness and other factors. These findings underscore the contextual importance of different influencing factors for enhancing fatigue resistance based on varying loading conditions.

Enhancement of the Microstructure and Fatigue Crack Growth Performance of Additive Manufactured Titanium Alloy Parts by Laser-Assisted Ultrasonic Vibration Processing

Post-processing techniques can efficiently improve the surface quality, address microstructural defects, and optimize mechanical properties in additively manufactured parts. Surface severe plastic deformation processes such as ultrasonic nanocrystal surface modification (UNSM) integrated with localized laser heating were explored to enhance the surface properties, microstructure as well as the fatigue crack growth properties (FCG) in both directions of built. We successfully induced greater plasticity flow and achieved beneficial refinement of the surface grain structure by precisely controlling the heat and impact energies during surface treatment process. The LA-UNSM process, with the parameters utilized in this study considerably decreased the FCG rates of treated samples, when compared to samples without surface treatment. Improved fatigue crack growth properties along vertical and horizontal orientations after the post-process treatment were attributed to the induced-microstructural changes, improved surface quality, induced compressive residual stresses through gradient structure deformation layer that was prepared on the surface of the material. The fractographic analysis revealed that the cracks mostly originated from the pores in the as-produced state. This observation shows a clear correlation between the surface treatment performed and a substantial improvement in fatigue crack growth resistance.

Effect of laser shock peening on fretting wear behaviour of AISI 304 stainless alloy

Unlike many other surface treatment techniques, such as shot peening (SP), low plasticity burnishing (LPB), ultrasonic surface rolling process (USRP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP) is a non-contact process. This means that LSP achieves surface modification without direct physical contact, thereby eliminating the risk of media contamination and undesired wear on the peening equipment. As a surface hardening technology, LSP tends to produce a hardened layer with a high gradient of residual stress (RS) in the near-surface, significantly enhancing wear resistance. The well-known wear theories applied for numerical prediction, whether Archard model or dissipated frictional-energy model, contain a multiplier for contact pressure and relative slip amplitude p·ds or shear stress and relative slip amplitude q·ds, respectively. These multipliers are sensitive to the mechanical properties near the surface. Additionally, the wear profile is governed not only by the wear effect but also by the deformation of materials. Therefore, to accurately evaluate the wear performance for surface-hardened materials, the influence of RS is hard to be overlooked. In this work, the finite element method (FEM) is utilised to construct a 3D numerical model, which ignores and considers RS, for both as-received and LSP-treated samples. Two distinct RS distributions induced by different scanning strategies (one- and five-time), are introduced in the finite element (FE) model. The numerical simulation results are then compared with the experimental data to verify the accuracy of the fretting wear model built in this study. On this basis, the impact of different RS distributions on fretting wear characteristics, including wear profile and volume, is extensively investigated. The findings reveal that higher amplitude RS can reduce the degree of fretting wear to a greater extent, highlighting the beneficial role of RS in enhancing wear resistance. Furthermore, the numerical models incorporating RS demonstrate superior predictive accuracy compared to those that omit RS. This naturally underscores the importance of integrating RS in numerical simulations of LSP and other surface-hardened materials.

Improving surface integrity and wear resistance of selective laser melted 316L stainless steel using ultrasonic nanocrystal surface modification

In this study, ultrasonic nanocrystal surface modification (UNSM) was employed to process 316L stainless steel fabricated using selective laser melting (SLM). The surface integrity, microstructure evolution, and mechanical behavior of this alloy before and after UNSM treatment were systematically characterized. The results show that the surface integrity and wear resistance of the alloy has been significantly improved due to the synergistic effect of grain refinement, work hardening, and beneficial compressive residual stresses that resulted from UNSM processing. The effect of the gradient structure and residual stress introduced by UNSM processing on the strengthening mechanism and its effect on friction and wear behavior have been discussed. The improved surface finish, the grain refinement layer, and the presence of compressive residual stress of the UNSM SLM 316L stainless steel alloy successfully demonstrated UNSM to be a promising post-processing surface treatment technology to enhance the fatigue performance of additively manufactured metallic materials.

Ultrasonic nanocrystal surface modification effect on reduction of hydrogen embrittlement in Inconel-625 parts fabricated via additive manufacturing process

With its considerable design flexibility, additive manufacturing, especially laser powder based fusion (PBF-LB) has been considered a possible method for fabricating metal parts needed in the hydrogen sector. However, hydrogen embrittlement of additively manufactured components is one of the essential issues that must be resolved before the practical application in the hydrogen industry. This study evaluates the effect of ultrasonic nanocrystal surface modification (UNSM) treatment on reducing hydrogen embrittlement in additively manufactured Inconel-625 alloy. The slow strain rate tensile test results of specimens with or without UNSM-treatment that were charged hydrogen gas at a high pressure of 700 bar for two weeks, it was confirmed that the elongation reduction decreased by about 6.3 % in the case of the UNSM-treated specimen. Even though the hydrogen concentration doubled after the UNSM-treatment, the decrease in elongation reduction indicates that the UNSM-treatment is effective in reducing hydrogen embrittlement. In addition, hardness, and microstructural inspection were employed to validate the mechanism of preventing hydrogen penetration after UNSM-treatment.

A Study on Surface Hardening and Wear Resistance of AISI 52100 Steel by Ultrasonic Nanocrystal Surface Modification and Electrolytic Plasma Surface Modification Technologies.

In this study, a surface hardening of AISI 52100 bearing steel was performed by ultrasonic nanocrystal surface modification (UNSM), and electrolytic-plasma thermo-cyclic surface modification (EPSM), and their effects on the wear resistance were investigated. To evaluate the impact of these treatments on the wear resistance, the friction tests under dry conditions were conducted using a ball-on-disk tribometer in accordance with ASTM G99. The microstructure of the samples before and after treatment was characterized by scanning electron microscopy. The micro-hardness with respect to the depth from the top surface was measured using a Vickers micro-hardness tester. Microstructural observations showed that EPSM treatment led to the formation of residual austenite in the surface layer, while UNSM treatment led to the formation of a surface severe plastic deformation layer on the surface of the samples. The increase in the micro-hardness of the treated layer was confirmed after UNSM at room temperature and after EPSM at different cycles. The highest increase in wear resistance was observed for the specimen treated by UNSM treatment at 700 °C and five cycles of EPSM treatment. In addition, the wear volume, which has correlation with the friction coefficient and hardness, was determined.

Experimental and numerical investigation of martensite phase transformation in austenitic stainless steel subjected to ultrasonic nanocrystal surface modification at room and cryogenic temperatures

This study aims to investigate the evolution of martensite volume fraction (ξ) following ultrasonic nanocrystal surface modification (UNSM) on metastable austenitic stainless steel 304L specimens at room and cryogenic temperatures using both numerical and experimental methods. A user subroutine (VUMAT) was utilized to implement a constitutive model that describes the phase transformation occurring in the target during the UNSM process. An alternative method was employed to simulate UNSM. The numerical predictions of residual stress (σres) and ξ exhibited good agreement with those measured experimentally. Finite element models were employed to undertake a comprehensive study of the impact of UNSM parameters on σres and ξ. The findings demonstrated that UNSM at cryogenic temperature produced significantly higher levels of compressive σres in comparison with UNSM at room temperature, while the depth of the layer with compressive σres and the extent of plastic deformation decreased. Based on the experimental and numerical findings, a significant value of ξ was observed to form within the subsurface region subsequent to UNSM at both temperature conditions. The value of ξ on the surface of UNSMed specimens at room and cryogenic temperatures was quantified using X-ray diffraction, resulting in respective values of 82 % and 88 %. Moreover, a significant increase in near-surface layer hardness for the UNSMed specimen at cryogenic temperature was observed, with a value of approximately 600 Vickers. This value is notably higher than the hardness of 480 Vickers obtained for the UNSMed specimens at room temperature.

Corrosion damage repair of 7075-T6 aluminum alloy by ultrasonic nanocrystal surface modification

This study explored the corrosion resistance of 7075-T6 aluminum alloy by immersing it in a 3.5% NaCl solution to induce corrosion damage, and subsequently repairing the sample surface using ultrasonic nanocrystal surface modification (UNSM). UNSM was found to effectively repair the defects on the surface of the pre-corroded sample and improve its stress corrosion crack (SCC) resistance. The improvement in corrosion resistance and SCC resistance of sample was mainly due to the compressive residual stress and grain refinement caused by UNSM, which not only improved the pitting resistance but also effectively inhibited the initiation and extension of stress corrosion cracks.

Controlling defects of laser-powder bed fusion processed 316L stainless steel via ultrasonic nanocrystalline surface modification

Metal additive manufacturing (MAM) offers an excellent capability for designing complex geometries with topology-optimized and near-net-shaped structures. The optimization-designed MAM parts with constrained volume require superior mechanical properties to broaden their utilization in the industry. However, the intrinsic defects generated during the building process deteriorate the mechanical functionality and limit utilization in various industrial applications. In this study, we propose a new strategy to reduce generated defects using ultrasonic nanocrystal surface modification (UNSM) on laser powder bed fusion (LPBF) processed 316L stainless steel. Subsurface pores and high surface roughness in MAM parts were significantly improved through the impact of UNSM treatment, and a gradient structure with mechanical incompatibility was developed. Consequently, the LPBF-processed samples after UNSM treatment show the excellent combination of strength and ductility, which is attributed to the high synergistic hardening from the gradient microstructure and the suppression of damage evolution by controlling built defects.

Effect of electropulsing-assisted ultrasonic nanocrystal surface modification on microstructures and hardness of additive manufactured Inconel 718

Additive manufacturing can process parts with complex shapes and has great application potential in the biomedical and aerospace industries. However, additively manufactured parts have a poor surface finish, high porosity, and large tensile residual stresses and thus have poor mechanical properties compared with traditional cast or forged parts. To address this issue, an innovative surface process, namely electropulsing-assisted ultrasonic nanocrystal surface modification (EP-UNSM) technology, is proposed. A pulsed current is exerted on the specimen to improve the metal plasticity during the UNSM processing, thereby increasing the effectiveness of strengthening. The results indicate that compared with UNSM, EP-UNSM can further improve the surface quality, surface hardness and the depth of the plastic deformation layer of the specimen. Moreover, it is observed that UNSM is more effective at higher peak current densities. In addition, compared with continuous current with identical thermal effect, pulsed current can more effectively improve the plasticity of Inconel 718, which proves the existence of the athermal effect of electroplasticity.