Ultrasonic Nanocrystalline Surface Modification Treatment Research Articles

Microstructural evolution and mechanical properties of laser-powder bed fusion processed 316L stainless steel with an ultrasonic-nanocrystalline surface modification

Because the surface roughness of additively manufactured (AM) metallic alloys affect their mechanical properties, surface post-treatment has become an attractive strategy for improving the performance of AM parts. Although several studies have revealed that surface treatment improves the mechanical properties of AM parts, changes in their surface morphologies and deformation mechanisms have not been well investigated. To solve this problem, in this study, the role of ultrasonic nanocrystalline surface modification (UNSM) treatment on the plastic deformation behavior of AM 316L stainless steel was investigated. The shear strain from the UNSM treatment induced severe grain refinement and crumbled traces at the surface of the as-built samples, causing a strength-ductility combination improvement compared to the non-treated sample. Moreover, the UNSM treatment removed the unmelted particles that relieved strain localization at the surface of the as-built sample during the plastic deformation process. Meanwhile, UNSM treatment in the machined sample reduced the surface quality, such as microcracks, which causes strength-ductility combination degradation. This result indicates that the post-surface mechanical treatment of the as-built metallic parts effectively improves the mechanical properties. This result was accomplished by inducing a gradient microstructure and a crumbled trace, which contribute to the strength improvement and the crack growth inhibition, respectively.

Post-building successive treatments using surface laser remelting and ultrasonic nanocrystalline surface modification for rough surface built via directed energy deposition

In this study, surface laser melting (SLR) and ultrasonic nanocrystalline surface modification (UNSM) were applied as post-building treatments to modify the surface of additively manufactured parts via directed energy deposition (DED). The DED building of STS316L powder was conducted on a substrate, and the deposited surface was irradiated with a laser of the DED equipment to perform SLR on the surface. Subsequently, the remelted surface was re-treated with UNSM, and the changes in each step were examined. Via the experiment, the as-built surface roughness and waviness of 12.5-μm Ra and 8.22-μm Wa, were improved to 2.3 μm and 2.5 μm, respectively, by the successive treatments of SLR and UNSM (denoted by SLRed-UNSMed). From the perspective of grain refinement by UNSM treatment, performing SLR with a small overlap followed by UNSM was determined to be effective in maximizing the effect of UNSM. The SEM and EBSD analysis results indicated that grain refinement occurred in a deeper region in SLRed-UNSMed than in the sample (denoted by UNSMed) that was treated solely with UNSM and no SLR. In addition, according to the pole figure analysis, the primary surface modification and grain reorientation in the (100) direction by SLR allowed the UNSM energy to be transferred more evenly and deeper. Meanwhile, high hardness and compressive residual stress were observed in SLRed-UNSMed, and a nano-indentation test confirmed an increase in the effective depth of UNSM relative to that of UNSMed. Based on this study, an SLR treatment followed by UNSM can be expected to achieve surface modification and improve the mechanical properties of additively manufactured products.

Mechanical property enhancement in gradient structured aluminum alloy by ultrasonic nanocrystalline surface modification

The large strength difference between hard and soft components in heterogeneous structured materials leads to the evolution of high back-stress hardening, which increases the strength and ductility of materials simultaneously. Moreover, the combination of high shear strain and elevated temperature allows an increase in the strength of low-melting temperature metallic alloys by grain refinement, solute migration, and clustering. In this study, to design a new heterogeneous microstructure in the aluminum alloy, both room temperature (RT) and high-temperature (HT) ultrasonic nanocrystalline surface modification (UNSM) were conducted, and their mechanical properties and microstructural evolutions were investigated. The large shear strain from the UNSM treatment reduces the grain size at the sample surface and creates a gradient structure. The combination of shear strain and elevated temperature during UNSM treatment induces solute migration at a certain depth of the specimens, resulting in the nano-sized Mg-rich particles at the surface region. Both grain refinement and precipitation at the surface region of the HT sample provide strong back-stress hardening in the early stages of deformation that enhances the strength and ductility of materials. Therefore, a high shear strain and control of processing temperature allow the design of a unique heterogeneous microstructure in low-melting temperature metallic alloys, which is a good strategy for enhancing the mechanical properties of sheet or thin metallic products.

Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy

Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S2PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta.

Improvement in Microscratch Resistance of Graphite by Surface Modification for Molding Applications

This paper deals with the improvement in surface properties and microscratch resistance of graphites by means of an ultrasonic nanocrystalline surface modification (UNSM) technique. The surface roughness and surface hardness of the untreated and UNSM-treated graphites were investigated using an atomic force microscopy (AFM) and a microhardness tester, respectively. The scratch resistance was assessed using a microscratch tester at a progressive load. Moreover, a Raman spectroscopy was employed to characterize the microstructure of graphites before and after UNSM treatment. The scratch test results revealed that the resistance to scratch of both UNSM-treated graphites was found to be better in comparison with the untreated graphites. The increase in scratch resistance of both UNSM-treated graphites may be mainly attributed to the reduced surface roughness and increased surface hardness by UNSM treatment. The graphite produced by Poco exhibited a higher resistance to scratch compared to that of the graphite produced by Mersen. The objective of this study is to extend the service life of three-dimensional (3D) cover glass moldings made of graphite by the application of UNSM treatment through the understanding the effects of surface roughness and surface hardness on the scratch defect generation behavior during glass molding process.

High Strength and Wear Resistance of Tantalum by Ultrasonic Nanocrystalline Surface Modification Technique at High Temperatures

Enhancing the strength of materials is of great concern in that the failures such as wear, corrosion and fatigue occur on the surface. A tantalum (Ta), which is a refractory metal, was subjected to severe plastic deformation induced by ultrasonic nanocrystalline surface modification (UNSM) technique at room- and high-temperatures of 200°C and 800°C. The mechanical properties and wear resistance of Ta before and after UNSM treatment were characterized by X-ray diffraction (XRD), hardness tester, and ball-on-disk tribometer, respectively. The UNSM treatment at 800°C led to the intensity reduction and broadening, and the diffraction peaks were shifted to lower angles, which means the presence of compressive residual stress and grain size refinement. The hardness of the UNSM-treated sample at room temperature was higher than that of the untreated one, and it was further increased with increasing the UNSM treatment temperature. In addition, the effect of UNSM treatment at high-temperature on wear resistance was significant than that of the UNSM treatment at room-temperature. We demonstrate the possibility of further increasing the mechanical properties and wear resistance of Ta by UNSM treatment at high-temperatures in comparison with the untreated and UNSM-treatment at room temperature, which would be beneficial for applications of Ta.

Strengthening of Ti-6Al-4V alloy by high temperature ultrasonic nanocrystal surface modification technique

Ti-6Al-4V alloy was subjected to heat treatment with (w/) and without (w/o) ultrasonic nanocrystalline surface modification (UNSM) treatment. The diffraction peaks of heat treatment w/o UNSM treatment samples were shifted to higher angles due to the tensile stress, while the heat treatment w/ UNSM treatment samples led to the intensity reduction and broadening, and the shift to lower angles, which may be attributed to the compressive residual stress, which increased with increasing the temperature. However, the peaks of heat treatment w/ UNSM treatment sample at 400°C were shifted to higher angles. This unusual behavior of the alloy is associated with a high tensile stress of α phase.

Microstructure and Friction Behavior of AISI 52100 and D2 Steels Subjected to Ultrasonic Nanocrystalline Surface Modification (UNSM) Technique at a High Temperature

In this study, two different AISI 52100 bearing and D2 tool steels were subjected to ultrasonic nanocrystalline surface modification (UNSM) technique at ambient and high temperature of 500 °C. The objective of this study is to characterize the microstructure and to investigate the effectiveness of UNSM technique on the friction and wear behavior of those steels. The friction and wear behavior of the specimens against AISI52100 bearing steel ball with a diameter of 10 mm was carried out using a micro-tribo tester under dry conditions. The hardness with respect to depth from the top surface was measured using a microhardness. The change in the microstructure of the specimens before and after UNSM treatment was characterized by scanning electron microscopy (SEM). The findings from this preliminary study are expected to be implemented to the bearings and tools to increase the efficiency and performance of the components.

Microstructural Characterization and Mechanical Properties of Stainless Steel Inlay Welded Dissimilar Materials

This present work was carried out to characterize the microstructure and mechanical properties of austenitic stainless steel (SS) 316L to dissimilar welding of Inconel 52 and Inconel 82 fillers that were treated by ultrasonic nanocrystalline surface modification (UNSM) technique. The microstructure and hardness map of the specimens were characterized by optical microscope (OM) and micro-hardness tester. The increase in hardness and refinement in grain size after UNSM treatment were found for the SS 316L/52 and SS 316L/82. In addition, the induced compressive residual stress in the surface layer of base SS 316L was measured. It is expected that the increased hardness into several microns in depth and modified microstructure with a severe plastically deformed surface layer by UNSM technique can increase the resistance to corrosion and extend the service life of pressurized water reactors (PWRs).

Low friction and high strength of 316L stainless steel tubing for biomedical applications

We propose herein a nondestructive surface modification technique called ultrasonic nanocrystalline surface modification (UNSM) to increase the strength and to improve the tribological performance of 316L stainless steel (SS) tubing. Nanocrystallization along nearly the complete tube thickness of 200μm was achieved by UNSM technique that was confirmed by electron backscatter diffraction (EBSD). Nano-hardness of the untreated and UNSM-treated specimens was measured using a nanoindentation. Results revealed that a substantial increase in hardness was obtained for the UNSM-treated specimen that may be attributed to the nanocrystallization and refined grains. Stress-strain behavior of the untreated and UNSM-treated specimens was assessed by a 3-point bending test. It was found that the UNSM-treated specimen exhibited a much higher strength than that of the untreated specimen. In addition, the tribological behavior of the untreated and UNSM-treated specimens with an outer diameter (OD) of 1.6mm and an inner diameter (ID) of 1.2mm was investigated using a cylinder-on-cylinder (crossed tubes of equal radius) tribo-tester against itself under dry conditions at ambient temperature. The friction coefficient and wear resistance of the UNSM-treated specimen were remarkably improved compared to that of the untreated specimen. The significant increase in hardness after UNSM treatment is responsible for the improved friction coefficient and wear resistance of the tubing. Thus, the UNSM technique was found to be beneficial to improving the mechanical and tribological properties of 316L SS tubing for various potential biomedical applications, in particular for coronary artery stents.

The possibility of reducing the reflectance and improving the tribological behavior of Si wafer by UNSM technique

In this study, mono- and poly-crystalline Si wafers, which are widely used in the manufacturing of high-performance solar cells, and nano- and micro-electromechanical systems (NEMS/MEMS), were subjected to ultrasonic nanocrystalline surface modification (UNSM) technique. The reflectance property of mono-crystalline Si wafer was improved after UNSM treatment in a certain wavelength but it reduced remarkably for poly-crystalline Si wafer. The hardness of both Si wafers was increased after UNSM treatment resulting in improvement of tribological behavior. According to the results of the present study, a UNSM technique might be considered as an alternative surface modification process to improve the properties of Si wafers for solar cell and NEMS/MEMS applications.

Friction Reduction and Wear Resistance Enhancement of SiC and Si3N4 Ceramics under Dry Conditions

ABSTRACTIn this study, an effort was made to control the friction and wear behavior of silicon carbide (SiC) and silicon nitride (Si3N4) ceramics using an ultrasonic nanocrystalline surface modification (UNSM) technique. The friction and wear behavior of the ceramic specimens was investigated using a ball-on-disk tribotester under dry conditions against two different Si3N4 and bearing steel (SUJ2) balls. The experimental test results revealed the possibility of controlling the friction and wear behavior of ceramics, where the friction coefficient and wear resistance of the specimens were improved by the UNSM technique. The hardness of the specimens also increased after UNSM treatment, but it decreased abruptly with increasing depth from the very top surface. Microscratch tests showed that the critical load of the specimens was improved by the UNSM technique. In addition, Raman spectra results revealed that no additional phase was detected after UNSM treatment, but the intensity decreased after UNSM treatment. Hence, the UNSM technique ensures stronger ceramics and enables better friction and wear behavior than available conventional sintered ceramics.

The migration of spheroidal cementite towards the surface in nanostructured AISI 52100 steel

The migration of spheroidal cementite (Fe3C) particles towards the surface by ultrasonic nanocrystalline surface modification (UNSM) technique in AISI 52100 bearing steel was discovered. The migration of Fe3C particles towards the surface, and their density and grain size at the top surface were assessed using an electron backscattered diffraction (EBSD) and a transmission electron microscopy (TEM), respectively. A mechanically continuous cyclic loading of UNSM treatment process refined the Fe3C particles into nano-sized particles along with ferrite (Fe3O4) nano-grains resulted in the migration of Fe3C particles towards the surface. The gradient nano-grained specimen with an increased Fe3C density exhibited a nearly 3 times higher hardness comparable to that of the coarse-grain one.

UNSM 기술을 이용한 초경의 기계적 특성변화

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si3N4) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

Effect of Ultrasonic Nanocrytalline Surface Modification on the Microstructural Evolution of Inconel 690 Alloy

Specimens of Inconel 690 were investigated after ultrasonic nanocrystalline surface modification (UNSM) using microhardness tests, electron backscattered diffraction, and transmission electron microscopy (TEM). After UNSM treatment, a 60% increase of hardness up to ∼310 µm in depth was observed. Layer-by-layer TEM analysis showed well-refined grains and twins in addition to the high dislocations density. The mechanism of the microstructure refinement was attributed to the development of nano-grains, twin structures, and dislocations.

Very high cycle fatigue behavior of SAE52100 bearing steel by ultrasonic nanocrystalline surface modification.

In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (- 10 μm) were refined to nanosize (- 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to - 400% and - 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by - 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen.

Microstructural Refinement of Al–Si Alloy Upon Ultrasonic Nanocrystalline Surface Modification Treatment

In this work, an Al-7 wt.% Si alloy, which is widely used as the structural materials in the automotive and aerospace industries for their high specific strength, was subjected to ultrasonic nanocrystalline surface modification (UNSM) treatment. After UNSM treatment, the effect of UNSM on the microstructural evolution of both Al grain and the dispersed Si particles was studied by using scanning electron microscope (SEM) and transmission electron microscope (TEM). Experimental results show that the ultra-fine grain (UFG, - 400 nm in size) structure is developed in the top surface layer (up to - 15 μm in depth). The coarse Si particles were refined and well dispersed in the UFG Al matrix. Cross-sectional TEM observation revealed that the grain refinement mechanism involved the formation of new grain boundaries dividing the coarse grain into UFG structure. Nanotwin and nanosize Si were formed within the original coarse Si particles. The presence of dispersed Si particles in the Al matrix accelerated the Al grain refinement process.

Characterization of the Nano-Scale Surface Layer of a Tempered Martensitic Steel Synthesized by Ultrasonic Nanocrystalline Surface Modification Treatment

Characterization of the Nano-Scale Surface Layer of a Tempered Martensitic Steel Synthesized by Ultrasonic Nanocrystalline Surface Modification Treatment

Improvement of the tribological properties of Al6061–T6 alloy under dry sliding conditions

The tribological properties of ultrasonic nanocrystalline surface modification (UNSM) treated Al6061–T6 alloy were investigated at various normal loads under dry sliding conditions. Electron backscattering diffraction (EBSD) analysis revealed a microstructure alteration of about 70μm in thickness generated by the UNSM technique. The friction test results showed that the friction coefficient and wear rate of the UNSM-treated specimen reduced by about 25 and 20% compared to that of the UNSM-free specimen, respectively. X-ray photoelectron spectroscopy (XPS) results showed that the oxide percentage on the worn surface increased, but that of carbon percentage decreased after the UNSM treatment.

Effects of ultrasonic nanocrystalline surface modification on the tribological properties of AZ91D magnesium alloy

A nanocrystalline surface layer of about 100μm thickness was generated on AZ91D Mg alloy using the ultrasonic nanocrystalline surface modification (UNSM) technique. Experiments were performed to study the effects of UNSM treatment on the tribological properties of AZ91D Mg alloy disk specimen and silicon nitride ceramic (Si3N4) ball combination. In the present study, UNSM-treated disk specimens with different nanocrystalline surface layer depths subjected to different impact loads were investigated. Electron backscatter diffraction (EBSD) observations revealed that the grain size at the top surface layer was decreased down to a few nanometers after UNSM treatment. The UNSM-treated specimens showed better tribological properties representing about 23% reduction in friction and about 30% in wear rate compared to that of the untreated specimens.