Ultrasonic Nanocrystal Surface Modification Research Articles

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.

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.

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

AbstractPost-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.

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.

Processing aluminum alloy with hybrid wire arc additive manufacturing and ultrasonic nanocrystalline surface modification to improve porosity, surface finish, and hardness

In this paper, a novel hybrid wire arc additive manufacturing (WAAM) and ultrasonic nanocrystal surface modification (UNSM) on porosity manipulation and surface properties of aluminum 5356 alloys was studied. The goal is to improve the quality of the WAAM-built part by eliminating bigger pores and reducing its size, reducing surface roughness, and increasing surface hardness. The as-built WAAM and WAAM-UNSM-treated samples were quantitatively studied for porosity using an X-ray micro-computed tomography (μ-CT). The surface roughness was measured on the surface profile of the same samples before and after UNSM treatment. Followed by the Vickers micro-hardness tests to evaluate the hardness modified by the influence of the UNSM treatment. It was found that the bigger pores in the as-built WAAM samples were eliminated and the medium-sized pores were shrunk to almost half the size after the UNSM treatment. Further, the UNSM treatment showed a significant improvement in both surface roughness and hardness on the WAAM Al5356 samples. This experimental work demonstrates the critical advantages of hybrid WAAM-UNSM in improving the qualities of the WAAM processed parts.

Influence of Laser Shock Peening and Ultrasonic Nanocrystal Surface Modification on Residual Stress, Microstructure, and Corrosion–Fatigue Behavior of Aluminum 7075-T6

Influence of Laser Shock Peening and Ultrasonic Nanocrystal Surface Modification on Residual Stress, Microstructure, and Corrosion–Fatigue Behavior of Aluminum 7075-T6

Ultrasonic nanocrystal surface modification (UNSM) of surface properties and residual stress in 300 M steels

The effects of different processing parameters of ultrasonic nanocrystal surface modification (UNSM) on surface properties of 300 M steel were investigated in this study. Experiments were performed using different scanning speeds, scanning intervals and static loads. The surface microhardness, roughness, wettability, appearance and residual stresses were evaluated for every set of processing parameter. The results showed that trenches, visible under microscope, formed in scanning direction indicating the contribution of burnishing effect of sliding motion of tungsten carbide (WC) ball tip on the surface of the specimen. It was observed that the surface roughness increases with a decrease in scanning speed as peening effect overtake the burnishing action of the WC tip and increase in the static load intensifies the peening effects in turn increasing the surface roughness. As static load increases, the surface begins to form microcracks and at very high static load the surface experiences severe surface damage. It was observed that the hardness and surface residual stresses of the processed sample increased with an increase in static load however at high static load the surface damage causes stress relaxation as material experiences localized fracture. Wettability of the processed surfaces was observed to be independent of the processing parameters.

Rapid formation of a surface ceramic protective film on Ti-6Al-4V alloy following laser-assisted ultrasonic nanocrystal surface modification

A surface ceramic protective film was prepared on Ti-6Al-4V alloy using laser-assisted ultrasonic nanocrystal surface modification technology (LA-UNSM). The uniform ceramic protective film, which was comprised of Al2O3 and small amounts of TiO2 and TiN, showed very strong adhesion to the substrate. LA-UNSM treatment dramatically increased the dislocation density and atomic diffusion rate by introducing thermomechanical activation energy, which further greatly reduced the energetic barriers of the oxide to nitride nucleation and growth. Due to the formation of a ceramic protective film and a nanocrystalline gradient reinforcement layer on the sample surface, the surface hardness was dramatically enhanced after LA-UNSM treatment. The electrochemical corrosion behavior in simulated seawater and the fretting wear behavior of samples were also investigated. The results revealed the ceramic protective film and gradient nanocrystalline layer introduced by LA-UNSM could substantially reduce the corrosion current density by 83 % and the wear volume by 90 % as compared to control samples. These results show that LA-UNSM effectively promotes the corrosion and wear property of titanium alloy through forming a ceramic protective film.

Mechanical Surface Treatments for Controlling Surface Integrity and Corrosion Resistance of Mg Alloy Implants: A Review

The present paper aims to provide an overview of the current state-of-the-art mechanical surface modification technologies and their response in terms of surface roughness, surface texture, and microstructural change due to cold work-hardening, affecting the surface integrity and corrosion resistance of different Mg alloys. The process mechanics of five main treatment strategies, namely, shot peening, surface mechanical attrition treatment, laser shock peening, ball burnishing, and ultrasonic nanocrystal surface modification, were discussed. The influence of the process parameters on plastic deformation and degradation characteristics was thoroughly reviewed and compared from the perspectives of surface roughness, grain modification, hardness, residual stress, and corrosion resistance over short- and long-term periods. Potential and advances in new and emerging hybrid and in-situ surface treatment strategies were comprehensively eluded and summarised. This review takes a holistic approach to identifying the fundamentals, pros, and cons of each process, thereby contributing to bridging the current gap and challenge in surface modification technology for Mg alloys. To conclude, a brief summary and future outlook resulting from the discussion were presented. The findings would offer a useful insight and guide for researchers to focus on developing new surface treatment routes to resolve surface integrity and early degradation problems for successful application of biodegradable Mg alloy implants.

New displacement-based finite element analysis method for predicting the surface residual stress generated by ultrasonic nanocrystal surface modification

Peening techniques can be applied to relieve high tensile residual stress, which is one of the main causes of primary water stress corrosion cracking (PWSCC). Ultrasonic nanocrystal surface modification (UNSM) is a peening technique that generates a high compressive residual stress on the surface of a structure. Finite element (FE) analysis can be utilized for quantitative surface stress prediction according to the UNSM in various materials and loading conditions. In this paper, a new method to predict the surface residual stress generated by UNSM process through FE analysis is proposed. In order to accurately simulate the UNSM process through FE analysis, it is necessary to define an equivalent displacement calculation method that can replace the complex load states of UNSM. For this, we proposed the new equivalent displacement calculation method based on the contact mechanics theory and the energy conservation law. The new equivalent displacement calculation method was validated by comparing the indentation depth obtained by single-path UNSM FE analyses and experiments under various loading conditions. The actual UNSM process is carried out in multiple paths over a large area of the structure. By applying the new equivalent displacement calculation method, the compressive residual stresses were calculated through multi-path UNSM FE analyses and compared with the results obtained from the multi-path UNSM experiments. The surface residual stress results of the experiments and analyses showed good agreement, and it was confirmed that the UNSM process can be simulated well if the new equivalent displacement calculation method is used for the FE analysis.

Improving fatigue life of additively repaired Ti-6Al-4V subjected to laser-assisted ultrasonic nanocrystal surface modification

Ultrasonic nanocrystal surface modification (UNSM) combined with localized laser heating (LA) were implemented to enhance the surface fatigue life of additively repaired Ti-6Al-4V alloy parts in this study. The effect of induced surface severe plastic deformation on microstructure development and grain refinement is analyzed. The results showed that surface metallurgical defects, hardness, residual stress, and roughness were significantly improved after LA-UNSM treatment. As a result of the improved surface textures and higher grain refinement, the fatigue life of the LA-UNSM treated samples was an order of magnitude longer. Surface free of pores and displaying a healthy topography provides evidence.

Study on Effects of Ultrasonic Nano-crystal Surface Modification on High-manganese Steels Built by Directed Energy Deposition

Study on Effects of Ultrasonic Nano-crystal Surface Modification on High-manganese Steels Built by Directed Energy Deposition