Ultrasonic Nanocrystal Surface Modification Treatment 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

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>

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.

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.

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.

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.

Superior gradient heterostructured alloys fabricated by laser powder bed fusion via annealing and ultrasonic nanocrystal surface modification

Developing metal additive manufactured (AM) parts with excellent mechanical properties broaden the utilization of AM parts in various industrial applications. Recently, gradient structures have received significant attention owing to their excellent mechanical properties. In this study, we propose a new strategy to obtain a superior gradient structure using annealing and ultrasonic nanocrystal surface modification (UNSM) on laser powder bed fusion (LPBF) fabricated 316 L stainless steel. The post-LPBF annealing treatment disturbed the cellular dislocation structure, which led to the optimized materials for gradient structure. The resulting gradient structure after the UNSM treatment has a thicker gradient layer with a significant strain partitioning between the domains than the LPBF followed by UNSM without annealing. As a result, the present LPBF-annealing-UNSM alloys show superior strength-ductility synergy compared to the LPBF-UNSM samples.

Higher wear-resistant surfacing at high temperatures using a hybrid cladding process

A novel hybrid cladding process is developed to control the mechanical properties of the inner metallic clad layer by combining direct energy deposition (DED) and ultrasonic nanocrystal surface modification (UNSM). The hybrid process allows the manipulation of the cladding layers' internal and external mechanical properties to the desired surface and bulk properties. To verify the usefulness of this method, the wear resistance test of the Inconel-718 cladding layer at high temperatures of 200 and 400 °C was performed, and it was confirmed that the wear resistance was improved to 25.4 % and 14.4 %, respectively. This work analyzes the wear-resistant characteristics with and without UNSM treatment in the DED process. The proposed method is a promising way to change the internal mechanical properties of the cladding layer with high controllability and repeatability.

Enhancement of sliding wear and scratch resistance of two thermally sprayed Cr-based coatings by ultrasonic nanocrystal surface modification

This study aims to identify whether mechanical surface treatment can improve the properties of thermal spray coatings for use in fuel-lubricated sliding conditions. In this study, we investigated the effects of ultrasonic nanocrystal surface modification (UNSM) technology on thermally sprayed chromium oxide (Cr2O3) and chromium carbide-nickel chromium (Cr3C2–NiCr) coatings and the resulting changes in sliding wear in fuels and scratch resistance. The improvement in coefficient of friction (COF) and specific wear rate (SWR) of the coatings after UNSM treatment was attributed to the reduced surface roughness, increased surface hardness, and the formation of tribo-layers (oxide) having lower shear strength with good lubricating properties. The wear mechanisms of the coatings involved plastic deformation leading to abrasive and oxidation modes.

A Comparative Study on Mechanical and Corrosion Behaviours of α/(α + β) Mg-Li Alloys Subjected to Ultrasonic Nanocrystal Surface Modification

Ultrasonic nanocrystal surface modification (UNSM) was applied to hot-rolled Mg-Li alloys (LAE361 and LA106). The microstructure, mechanical properties, deformation mechanisms, and corrosion resistance properties of these alloys after UNSM treatment were systematically studied. Significant improvement in surface hardness and decrease in surface roughness were achieved by UNSM treatment. Meanwhile, the basal texture intensity of the Mg-Li alloys reduced significantly, and several deformation twins appeared on the surface layer. The α phase of the surface layer underwent twin deformation and basal plane slip. The fibre textures in the β phase of LA106 Mg-Li alloy changed from γ and η to α and ε, which mainly resulted in the dislocation slip. More importantly, UNSM treatment exhibited enhanced strength and improved plasticity of LAE361 and LA106 Mg-Li alloys. The corrosion current density of LAE361 Mg-Li alloy reduced approximately 29.3% by UNSM treatment, while it increased the corrosion current density of LA106 Mg-Li alloy by 189.7%. These studies show that the application of UNSM to improve the corrosion resistance of duplex phases of LA106 Mg-Li alloy needs further investigation.

Effect of Ultrasonic Nanocrystal Surface Modification Treatment at Room and High Temperatures on the High-Frequency Fatigue Behavior of Inconel 718 Fabricated by Laser Metal Deposition

In this work, the effect of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT) on the high-frequency fatigue behavior of Inconel 718 alloy fabricated by laser metal deposition (LMD) process was experimentally investigated. UNSM treatment at RT and HT modified a surface morphology and produced a nanostructured surface layer with a thickness of approximately 120 and 140 µm, respectively. The surface roughness of the untreated sample was reduced, while the surface hardness was notably increased after the UNSM treatment at RT and HT. Both increased with increasing the UNSM treatment temperature. Fatigue behavior of the untreated samples at various stress levels was slightly improved after the UNSM treatment at RT and HT. This is mainly due to the formation of a fine grained nanostructured surface layer with reduced porosity and highly induced compressive residual stress. Fatigue mechanisms of the samples were comprehensively discussed based on the quantitative SEM fractographic analysis.

Application of crosswise repetitive ultrasonic nanocrystal surface modification treatment to Inconel 690 alloy: Efficiency of single-path and multi-paths

In this study, the efficiency of crosswise repetitive ultrasonic nanocrystal surface modification (CR-UNSM) treatment on surface characteristics, tribological and fatigue properties of single and multi (double, triple, quadruple and quintuple) treated Inconel 690 alloy was investigated. All the CR-UNSM-treated specimens demonstrated better tribological and fatigue performance in comparison with the untreated specimen. Quintuple CR-UNSM-treated specimen demonstrated the lowest coefficient of friction (COF) and specific wear rate (SWR) among untreated and other CR-UNSM-treated specimens, while triple CR-UNSM-treated specimen was found to be the most effective in terms of fatigue performance. The surface roughness of Inconel 690 alloy was significantly reduced after single CR-UNSM treatment, afterwards it was gradually roughened with increasing the number of CR-UNSM treatment. The surface hardness along with hardened surface layer and also compressive residual stress (CRS) were increased with increasing the number of CR-UNSM treatment. Every CR-UNSM treatment was capable of refining coarse grains into nano-scale grains, where the higher number of CR-UNSM treatment the thicker nanostructured surface layer (NSL) and the finer grain size.

Through-Thickness Microstructures and Yield Strength Enhancement for AZ31 Mg Sheets Treated by Ultrasonic Nanocrystal Surface Modification

An ultrasonic nanocrystal surface modification (UNSM) technique was applied to a 1-mm thick AZ31 magnesium sheet. UNSM is a relatively new surface modification technique in which a hard, hemispherical tip (2.38 mm in diameter) strikes the surface at an ultrasonic frequency to induce plastically deformed gradient microstructures and deep compressive residual stresses through the thickness. After the UNSM treatment, the through-thickness microstructures were thoroughly investigated using electron microscopy and electron backscatter diffraction analysis. The through-thickness microstructures revealed zones that were severely deformed (down to 200 µm from the surface) and twin-dominated (200~300 µm deep from the surface). The severely deformed zone consisted of shear banding, grain subdivision and reorientation, due to the strong plastic deformation, accompanied by the formation of {10<math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent='true'><mn>1</mn><mo>−</mo></mover></math>2} tensile twins (despite compressive strikes by the hemispherical tip), {10<math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent='true'><mn>1</mn><mo>−</mo></mover></math>1}-{10<math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent='true'><mn>1</mn><mo>−</mo></mover></math>2} double twins and {10<math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent='true'><mn>1</mn><mo>−</mo></mover></math>1} compression twins. The cause for tensile twinning was examined through a literature survey. In the twin-dominated zone, the twining activity prevailed as the slip activity gradually decayed through the thickness. The UNSM-induced hardness and microstructure enhancement was found to be effective down to about 300~400 μm deep from the surface. Finally, the source of the increase in yield strength after the UNSM treatment of the AZ31 sheet was analyzed, and focused on individual cases of microstructural enhancement in the severely deformed zone and the twin zone, and the compressive residual stress.

Method of ultrasonic nano-crystal surface modification for improvement of surface characteristics of AISI D2 heat-treated with different tempering conditions

AISI D2, an alloy tool steel, has been widely used as a cold-work die steel because of its excellent wear resistance, toughness, and machinability. However, when it is used as a mold or tool under a high load, high hardness and wear resistance are required to improve its service life. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM), a local surface hardening technology, to the surface of D2 steel. To maximize the surface improvement effect achievable through UNSM, it is important to select the optimal process conditions according to the characteristics of the base metal. Therefore, the effects of UNSM were compared for different initial hardness values of D2 in this study. To this end, the base metal was subjected to different heat treatment conditions to exhibit different hardness values (approximately 40, 45, 50, and 55 HRc). Changes in the surface of the base metal were observed according to the three main parameters of the UNSM process: the load, inter-pass interval, and feed rate. No significant changes in the surface roughness and hardness were caused by the feed rate. As the inter-pass interval of UNSM decreased and the static load increased, the surface roughness of the base metal increased. However, the specimen with low initial hardness (D2-H40), the roughness improvement decreased as the load increased. On the other hand, the surface hardness improvement increased as the inter-pass interval decreased and the load increased regardless of the initial hardness of the base metal. It also was found that the specimen with the highest initial hardness (D2-H55) exhibited the greatest hardness improvement rate of 9% and smallest hardened layer thickness of 220 μm. In addition, the largest compressive residual stress (− 1,130.6 MPa) was formed on the surface of D2-H55 after UNSM, which occurred because the base metal with high initial hardness had limited plastic flow due to fine grains and low ductility, causing thus the energy repeatedly delivered by UNSM to be concentrated in a limited area. Consequently, reducing the inter-pass interval is effective on improving the surface roughness and hardness regardless of the material hardness. However, the load must be applied at an appropriate level, depending on the material hardness. Therefore, when D2 is heat-treated and used according to the product requirements, it will be effective to consider the changes after UNSM treatment based on hardness after heat treatment that were derived in this study.

Effects of ultrasonic nanocrystal surface modification on dry tribological and slurry erosion performance of non-reinforced and reinforced Ni-based microwave clads

The aim of this study is to find out whether ultrasonic nanocrystal surface modification (UNSM) is capable of having a considerable impact on dry tribological and slurry erosion performance of Ni-based microwave clads. The non-reinforced and Cr7C3 reinforced Ni-based clads were produced using a microwave cladding method. The application of UNSM treatment reduced the surface roughness of the clads. The UNSM-induced effective depth of 200–350 μm refines the grain structure that influences the hardness. Interestingly, the effectiveness of UNSM treatment was weakened for the non-reinforced clad in dry tribology, whereas similar results were obtained for the reinforced clad in slurry erosion testing. Wear and slurry erosion mechanisms were comprehensively discussed based on the worn-out surface characterizations.

Effect of ultrasonic nanocrystal surface modification temperature: Microstructural evolution, mechanical properties and tribological behavior of silicon carbide manufactured by additive manufacturing

This study deals with the improvement in mechanical and tribological properties of silicon carbide (SiC) manufactured by additive manufacturing (AM) through ultrasonic nanocrystal surface modification (UNSM) at 23 °C (room temperature - RT) and 900 °C (high temperature - HT). It was demonstrated that the UNSM treatment temperature had a great effect on the mechanical and tribological properties of the as-printed SiC. The R a and R z surface roughness values of the as-printed SiC sample were reduced from 10.5 μm down to 6.5 μm and from 47.0 μm down to 25.9 μm after UNSM treatment at RT, respectively. Furthermore, it was further reduced down to 5.5 μm and 21.2 μm with increasing the UNSM treatment temperature. UNSM treatment at RT and HT was able to increase the surface hardness of the as-printed SiC sample from 2100 HV up to 2500 HV and 2700 HV, respectively. The coefficient of friction (COF) of the as-printed SiC sample was approximately 0.187, which reduced down to 0.172 and 0.141 after UNSM treatment at RT and HT, respectively. The specific wear rate (SWR) of the as-printed sample was 2.61 × 10 −12 mm 3 /N × m, and decreased to 1.58 × 10 −12 mm 3 /N × m and 6.46 × 10 −13 mm 3 /N × m after UNSM treatment at RT and HT, respectively. The results of this investigation help improve the performance of AM-based SiC that is the potential candidate for many high-temperature applications such as nuclear, aerospace, optical, etc. instead of SiC manufactured by sintering method. • The SiC-Si samples were manufactured by additive manufacturing method. • UNSM was applied to SiC-Si at RT and HT. • UNSM temperature increase resulted in finer grains and more deformation twins. • Ratio of SiC vs. Si changed after UNSM treatment at RT and HT. • The tribological properties of SiC-Si improved by UNSM at RT and HT.

Effect of the Thermomechanical Treatment on the Corrosion of UNSM Processed Inconel 718: An Electrochemical Study

In this work, the influence of thermal (TT), mechanical, and thermomechanical (TMT) treatments using the ultrasonic nanocrystal surface modification (UNSM) on the corrosion protection properties of Inconel 718 was studied, correlating the changes in the electrochemical properties with the promoted microstructure. The UNSM treatment had a grain refinement effect on the top surface, reducing the grain size from 11.5 to 7.4 µm for the first 10 µm in depth. The high grain boundary density, due to the grain refinement, enabled a faster growth of the passive film. The impedance showed a decrease in the charge transfer resistance by three orders of magnitude, from 106 to 103 Ω cm2 for as-received to 1000 °C, as the TT temperature crossed the solvus of the γ′/γ″ and approached the solvus of the δ-phase. The UNSM treatment lowered the pitting corrosion susceptibility, increasing the charge transfer resistance and decreasing the effective capacitance of the double layer, leading to the thickest passive film with 6.8 nm.

Fatigue life extension of additively manufactured Nickel-base 718 alloy by nanostructured surface

In this study, the beneficial effect of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT) on the mechanical properties and fatigue performance of Nickel-base 718 alloy that is fabricated by laser directed energy deposition (LDED) process was investigated. UNSM treatment at RT and HT demonstrated a significant enhancement in fatigue performance by approximately of 43% and 57%, respectively. This can be attributed to the introduction of a high compressive residual stress (CRS) and the generation of nanostructured surface layer. Moreover, it was found that the surface roughness reduced, while the hardness increased after UNSM treatment at RT and HT. Furthermore, it was found by analysing the fatigued surfaces that the main crack initiation site was located at the subsurface for the UNSM-treated samples, while it was located at the top surface for the untreated ones. Introduction of a high CRS by UNSM treatment at RT and HT shifted a crack initiation site into subsurface.

Fatigue performance rejuvenation of corroded 7075-T651 aluminum alloy through ultrasonic nanocrystal surface modification

In this study, ultrasonic nanocrystal surface modification (UNSM) was used to rejuvenate the fatigue performance of pre-corroded 7075-T651 aluminum alloy. The fatigue life of specimens subjected to pre-corrosion and burnishing was found to be only slightly higher than that of corroded specimens, while the fatigue life of the specimens subjected to pre-corrosion and UNSM treatment was twenty times higher than that of the corroded specimens. The findings of this study demonstrate that the repair of the corroded surface layer, surface work-hardening, and beneficial compressive residual stress induced by UNSM are responsible for the fatigue performance rejuvenation of the pre-corroded alloy.