Ultrasonic Nanocrystal Surface Modification Treatment Research Articles

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.

Effects of Pre- and Post-Carburizing Surface Modification on the Tribological and Adhesion Properties of Heat-Resistant KHR 45A Steel for Cracking Tubes.

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the tribological properties and scratch-induced adhesion behavior of a heat-resistant KHR 45A steel cracking tube, which is used for the pyrolysis process, were investigated. The main objective of this study is to investigate the effects of pre- and post-carburizing UNSM treatment on the tribological and adhesion performances of carburized domestic KHR 45A (A) steel and to compare the results with the existing carburized Kubota-made KHR 45A steel (B). A carburizing process was carried out on the polished and UNSM-treated KHR 45A steel substrates, which were cut out from the cracking tube, at 300 °C heat exposure for 300 h. The thickness of the carburizing layer was about 10 μm. UNSM technology was applied as pre- and post-carburizing surface treatment; both reduced the friction coefficient and wear rate compared to that of the carburized KHR 45A steel substrate. It was also found that the application of UNSM technology increased the critical load, which implies the improvement of adhesion behavior between the carburizing layer and the KHR steel substrate. The application of UNSM technology as pre- and post-carburizing surface treatment could help replace carburized Kubota-made KHR 45A steel (B) thanks to the improved tribological performance, enhanced scratch resistance, load bearing capacity, and adhesion of domestic KHR 45A (A) steel.

Improving plain and fretting fatigue resistance of A100 steel using ultrasonic nanocrystal surface modification

In this study, ultrasonic nanocrystal surface modification (UNSM) was used to improve plain and fretting fatigue properties of A100 steel. Results showed that an obvious plastic deformation layer was induced in A100 steel, and the martensite microstructure was remarkably refined. In addition, surface compressive residual stress after UNSM treatment was enhanced to 1700 MPa due to the severe lattice distortion. The increased surface hardness and the presence of beneficial compressive residual stresses after UNSM treatment significantly enhanced the plain/fretting fatigue resistance of A100 steel by retarding fatigue crack nucleation and propagation.

Effect of multiple ultrasonic nanocrystal surface modification on surface integrity and wear property of DZ2 axle steel

Ultrasonic nanocrystal surface modification (UNSM) treatments with different numbers of rolling passes are employed to enhance the surface integrity and the wear resistance of DZ2 axle steel for high-speed trains. In this study, microstructures, residual stress, and wear properties of the DZ2 axle steel after multiple UNSM treatments were investigated. The results showed grain refinements in the near-surface layer of the DZ2 axle steel after multiple UNSM treatments. Compared with the untreated sample, the compressive residual stress of the surface increased from −73 to −703 MPa, and the surface microhardness increased from 220 to 283 HV 0.2 . The results from wear tests showed that the sample with UNSM treatment of three rolling passes exhibited a significantly enhanced wear resistance under sliding conditions. • A nanostructured surface layer was fabricated on DZ2 axle steel through multiple UNSM processing. • Multiple UNSM treatment can introduce high compressive residual stress and hardness. • The surface-modified layer reduces the coefficient of friction. • The depth of deformed layer increases with increasing number of rolling pass.

Better Surface Integrity and Tribological Properties of Steel Sintered by Powder Metallurgy.

The current research reports the improvement in surface integrity and tribological characteristics of steel prepared using a powder metallurgy (PM) by ultrasonic nanocrystal surface modification (UNSM) at 25 and 300 °C. The surface integrity and tribological properties of three samples, namely, as-PM, UNSM-25 and UNSM-300 were investigated. The average surface roughness (Ra) of the as-PM, UNSM-25 and UNSM-300 samples was measured using a non-contact 3D scanner, where it was found to be 3.21, 1.14 and 0.74 µm, respectively. The top surface hardness was also measured in order to investigate the influence of UNSM treatment temperature on the hardness. The results revealed that the as-PM sample with a hardness of 109 HV was increased up to 165 and 237 HV, corresponding to a 32.1% and 57.2% after both the UNSM treatment at 25 and 300 °C, respectively. XRD analysis was also performed to confirm if any changes in chemistry and crystal size were took place after the UNSM treatment at 25 and 300 °C. In addition, dry tribological properties of the samples were investigated. The friction coefficient of the as-PM sample was 0.284, which was reduced up to 0.225 and 0.068 after UNSM treatment at 25 and 300 °C, respectively. The wear resistance was also enhanced by 33.2 and 52.9% after UNSM treatment at both 25 and 300 °C. Improvements in surface roughness, hardness and tribological properties was attributed to the elimination of big and deep porosities after UNSM treatment. Wear track of the samples and wear scar of the counter surface balls were investigated by SEM to reach a comprehensive discussion on wear mechanisms. Overall, it was confirmed that UNSM treatment at 25 and 300 °C had a beneficial effect on the surface integrity and tribological characteristics of sintered steel by the PM that is used in a shock absorber for a car engine.

Artificial neural network-based prediction model of residual stress and hardness of nickel-based alloys for UNSM parameters optimization

Ultrasonic Nanocrystal Surface Modification (UNSM) is known as one of the surface treatment techniques that utilizes an ultrasonic vibration energy to improve mechanical properties and performance of materials. The dynamic nature of this surface treatment process deforms the top surface and subsurface of materials with a very high strain rate, which makes the direct observation of residual stress and refined layers very difficult. In this study, a novel alternative approach is proposed that is based on the artificial neural network (ANN) concept for predicting residual stress and hardness of various nickel-based alloys that have been subjected to UNSM treatment. Experimental measurement data were used in the ANN training process and validation. The trained model showed the capability of predicting residual stress and hardness accurately with a Pearson correlation value (R) of 0.988 and 0.996, a root mean squared error (RMSE) of 84.231 and 17.028, and a mean absolute error (MAE) of 68.586 and 13.450 for residual stress and hardness models when tested using the test dataset, respectively. It can be concluded that ANN as the alternative approach is a suitable method for accurately performing prediction for practical use in the absence of a mathematical model. Since the experimental result was used in the ANN model training process, the predicted result by the ANN model appears to agree with the experimental results of the UNSM treatment. Because of these demonstration results, the ANN-based prediction model can be used as a tool to optimize the UNSM treatment parameters.