UNSM-treated Specimens Research Articles

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.

VHCF, Tribology Characteristics and UNSM Effects of Bainite and Martensite Spring Steels

It has been reported that the duplex bainite microstructure obtained by austempering (AT) shows higher strength, ductility and impact toughness than quench and tempered (QT) martensite structure in SAE9254 spring steel. However, there seems to be no research on the very high cycle fatigue (VHCF) and tribology characteristics of bainite structure for durability design of next generation spring steel from the perspective of engineering and industrial applications. This is a follow-up study that quantitatively analyzed the mechanical properties, microstructural deformation characteristics, and impact toughness of bainite and martensite using EBSD (Electron Backscatter Diffraction) and SEM (Scanning Electron Microscope) analyses. In this study, VHCF, HCF, tribology characteristics and UNSM (ultrasonic nanocrystal surface modification) effects under duplex bainite and single martensite microstructures were quantitatively studied and analyzed by fracture mechanics from the engineering and industrial point of view to improve durability and weight reduction in spring steels. The bainite AT and martensite QT specimens showed a 56% and 33% increase in fatigue limit for as received AR specimens. Fisheye cracks in duplex bainite AT specimens are similar to ‘facet internal cracks’ that initiated in the absence of inclusions. Generally fisheye crack fracture mode is preferred in VHCF, but fisheye crack was not found in the QT and the AR specimens at all. The UNSM-treated specimens showed fatigue limits that were about 33~50% higher than the untreated specimens.

Microstructure and mechanical properties of CoCrFeMnNi high entropy alloy with ultrasonic nanocrystal surface modification process

In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification (UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The near-surface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.

Improvement in mechanical properties and fretting wear of Inconel 718 superalloy by ultrasonic nanocrystal surface modification

Inconel 718 (IN718) superalloy specimens were treated with ultrasonic nanocrystal surface modification (UNSM) at room and high temperatures (RT and HTs). The purpose of this work is to investigate the UNSM temperature dependence of the microstructure, fretting wear resistance and mechanical properties such as surface hardness, yield strength, ultimate tensile strength and ductility. A nanocrystalline surface layer with a certain depth was generated on the surface and in the near-surface region of the UNSM-treated specimens. Results revealed that the surface hardness of the specimen subjected to UNSM at RT was increased by 35% compared with that of the untreated ones, and the hardness was further increased of the specimen subjected to UNSM at HTs of 400 and 600 °C compared with the UNSM at RT. The friction and wear performance of IN718 superalloy was evaluated using a ball-on-disk tribometer fretted against SAE52100 bearing steel. The friction coefficient of the UNSM-treated specimens at RT, HTs of 400 and 600 °C was reduced from 0.68 to 0.65, 0.10 to 0.08 and 0.077 to 0.03 at fretting testing temperatures of 25 and 400 °C, respectively. The fretting wear resistance of the UNSM-treated specimens at RT, HTs of 400 and 600 °C was enhanced compared with that of the untreated specimen. The fretting wear resistance of the specimens was further enhanced by increasing the fretting wear testing temperature. It was concluded that the UNSM temperature played a vital role in further increasing the fretting wear resistance, surface hardness, yield and ultimate tensile strengths of IN718 superalloy for nuclear applications.

The effect of ultrasonic nanocrystal surface modification on low temperature nitriding of ultra-high strength steel

In this research, a surface plastic deformation layer was induced on 300M ultra-high strength steel using ultrasonic nanocrystal surface modification (UNSM). The UNSM-treated and control specimens were then nitrided at 450 °C for 6 h. After gas nitriding, the microstructure, corrosion and wear resistance of 300M steel with and without UNSM pre-treatment were investigated. After nitriding, the UNSM-treated specimens generated a dense surface nitride layer that was thicker than that of the control specimens. The high defect density and refined lath martensite induced by UNSM were found to accelerate the nitrogen diffusion and efficiency. X-ray diffraction patterns revealed that α-Fe phase occupied the largest proportion in the nitriding layer of specimens without UNSM pre-treatment. However due to the higher nitriding efficiency, the main phase of UNSM-treated specimens after nitriding was found to be ε-Fe2-3N. Compared with the specimens without pre-treatment, UNSM-treated specimens exhibited higher surface hardness as well as higher corrosion and wear resistance after nitriding.

Significant improvement in cell adhesion and wear resistance of biomedical β-type titanium alloy through ultrasonic nanocrystal surface modification

A novel β-type Ti–29Nb–13Ta–4.6Zr (TNTZ) alloy with a low Young's modulus, high bio-corrosion resistance, and excellent biocompatibility has been recently introduced for implant applications. Here, ultrasonic nanocrystal surface modification (UNSM) treatment was applied to TNTZ alloy to improve its wear resistance and biofunctionality. Application of UNSM to a TNTZ alloy resulted in the generation of a nanostructured surface layer. The wear resistance of the UNSM-treated specimen was observed to be more than 7 times higher than that of the untreated one. Cell culture tests indicated that MC3T3 cells adhered and spread more readily on the UNSM-treated specimen than on the untreated one. MTT assays after 1 and 4 days in culture also indicated enhancement of cell proliferation on the UNSM-treated specimen than that of the untreated one. Live/dead assay revealed no significant cytotoxicity in either substrate. The significant improvement of cell adhesion, spreading, and proliferation on the UNSM-treated TNTZ alloy specimen were attributed to both grain refinement and micro-patterned surface effects. These results demonstrate that UNSM-treatment not only improves the wear resistance of TNTZ alloy, but also enhances its biocompatibility, which makes it a strong candidate for applications in medical implants.

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.

Effects of ultrasonic nanocrystal surface modification on the wear and micropitting behavior of bearing steel in boundary lubricated steel-steel contacts

An ultrasonic nanocrystal surface modification (UNSM) technique has been used to treat AISI 52100 steel specimens and thrust ball bearing raceways. Tribological performances of untreated specimens were compared to UNSM-treated specimens in reciprocating sliding and rolling/sliding contact under boundary lubricated conditions. Friction and wear coefficients, micropitting, and changes in surface profiles and surface roughness of the specimens were studied. Results showed that UNSM treated specimens had higher wear and micropitting resistance than the untreated specimens. The improvements in wear and micropitting resistance may be attributed to increased surface hardness, refined grain sizes and compressive residual stress near surface region as a result of UNSM treatment. The UNSM technique has been proven to be a powerful tool to improve the durability and tribological performance of contacting surfaces of mechanical components such as bearings, gears, and seals.

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.

Synergy Effect of Ultrasonic Nanocrystalline Surface Modification and Laser Surface Texturing on Friction and Wear Behavior of Graphite Cast Iron

ABSTRACTLaser surface texturing (LST) followed by an ultrasonic nanocrystalline surface modification (UNSM) process was applied to graphite cast iron to improve the friction and wear behavior. The surface hardness of the UNSM-treated and UNSM + LST-treated specimens was increased significantly compared to the polished and LST-treated specimens. The friction and wear behavior of the specimens was assessed using a ball-on-disk friction tester at an applied load of 10 N and a speed of 5 cm/s in both dry and lubrication conditions. The friction coefficient of the UNSM-, LST-, and UNSM + LST-treated specimens reduced in both dry and lubrication conditions compared to the polished specimen by 64, 30, and 64% and 63, 67, and 75%, respectively. In lubrication condition, the friction coefficient of the UNSM- and LST-treated specimens was further reduced by about 30 and 25% by UNSM + LST processes. In dry condition, the UNSM + LST-treated specimen exhibited a reduction in the friction coefficient of 46% compared to the LST-treated specimen, whereas no reduction in friction coefficient was found compared to the UNSM-treated specimen. The wear resistance of the UNSM-, LST-, and the UNSM + LST-treated specimens was enhanced by 22, 11, and 37% in the dry condition, respectively, whereas minuscule wear was observed in the lubrication condition that was difficult to quantify in our experiment. UNSM and LST processes were effectively combined to improve the friction and wear behavior of graphite cast iron.

Microstructural evolution and surface properties of nanostructured Cu-based alloy by ultrasonic nanocrystalline surface modification technique

A nanostructured surface layer with a thickness of about 180μm was successfully produced in Cu-based alloy using an ultrasonic nanocrystalline surface modification (UNSM) technique. Cu-based alloy was sintered onto low carbon steel using a powder metallurgy (P/M) method. Transmission electron microscope (TEM) characterization revealed that the severe plastic deformation introduced by UNSM technique resulted in nano-sized grains in the topmost surface layer and deformation twins. It was also found by atomic force microscope (AFM) observations that the UNSM technique provides a significant reduction in number of interconnected pores. The effectiveness of nanostructured surface layer on the tribological and micro-scratch properties of Cu-based alloy specimens was investigated using a ball-on-disk tribometer and micro-scratch tester, respectively. Results exhibited that the UNSM-treated specimen led to an improvement in tribological and micro-scratch properties compared to that of the sintered specimen, which may be attributed to the presence of nanostructured surface layer having an increase in surface hardness and reduction in surface roughness. The findings from this study are expected to be implemented to the automotive industry, in particular connected rod bearings and bushings in order to increase the efficiency and performance of internal combustion engines (ICEs).

Wear and chattering characteristics of rail materials by ultrasonic nanocrystal surface modification

Stick-slip wear, sliding wear, rolling contact wear, fatigue failure and chattering are persistent problems of a wheel-rail interface, especially at corner track. Generally, high strength alloy and heat-treated rail were used at corner track in order to improve the service life and chattering level, but these targets still remain as unceasing challenge subject. Ultrasonic nanocrystal surface modification (UNSM) was applied to rail materials with the aim of replacing with heat treatment and/or improving the service life of rails. In this study, the mechanical and wear properties of the untreated and UNSM-treated specimens which were prepared from normal and heat treated rails. Friction and wear tests were performed to measure the friction coefficient and the amount of wear. Results revealed that the wear performance of the UNSM-treated specimens was improved due to the increased hardness and induced compressive residual stress after UNSM treatment. The wear mechanism of the UNSM-treated specimens was explained with the changes in surface properties of rail materials.

Rotary bending fatigue properties of Inconel 718 alloys by ultrasonic nanocrystal surface modification technique

This study investigates the influence of ultrasonic nanocrystal surface modification (UNSM) technique on fatigue properties of SAE AMS 5662 (solution treatment) of Inconel 718 alloys. The fatigue properties of the specimens were investigated using a rotary bending fatigue tester. Results revealed that the UNSM-treated specimens showed longer fatigue life in comparison with those of the untreated specimens. The improvement in fatigue life of the UNSM-treated specimens is attributed mainly to the induced compressive residual stress, increased hardness, reduced roughness and refined grains at the top surface. Fractured surfaces were analysed using a scanning electron microscopy (SEM) in order to give insight into the effectiveness of UNSM technique on fracture mechanisms and fatigue life.

초음파나노표면개질 기술을 적용한 초경의 기계적특성 및 마모 연구

In this study, we investigated the effectiveness of an ultrasonic nanocrystal surface modification (UNSM) technique on the mechanical and wear properties of tungsten carbide (WC). The UNSM technique is a newly developed surface modification technique that increases the mechanical properties of materials by severe plastic deformation. The objective of this study was to improve the wear resistance of press die made of WC by applying the UNSM technique. We observed the microstructures of the untreated and UNSM-treated specimens using a scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the chemical composition. The SEM observations showed the pore size and the number of pores decreased after the UNSM treatment. We assessed the wear behavior of both the untreated and UNSM-treated specimens using a scratch test. The test results showed that the wear resistance of the UNSM-treated specimens increased by about 46% compared with the untreated specimens. This may be attributed to increased hardness, reduced surface roughness, induced compressive residual stress, and refined grain size following the application of the UNSM technique. In addition, we found that the UNSM treatment increased the carbon concentration to 63% from 33%. We expect that implementing the findings of this study will lead to an increase in the life of press dies.

초음파나노표면개질기술을 이용한 저널베어링 마찰 및 피로특성 연구

In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.

Wear mechanisms of silicon carbide subjected to ultrasonic nanocrystalline surface modification technique

A modified surface layer with a thickness of about 4µm was produced at the top surface of sintered silicon carbide (SiC) by ultrasonic nanocrystalline surface modification (UNSM) technique. The objective of this study is to investigate the effectiveness of modified surface layer on the tribological properties and to give insight into the wear mechanisms of SiC. The tribological properties of the untreated and UNSM-treated SiC disk specimens against silicon nitride (Si3N4) ceramic ball were investigated using a ball-on-disk tribometer at normal loads of 1 N, 5 N and 10 N under water-lubricated conditions. Results revealed that the friction coefficient was found to be 0.08 and 0.065 for the untreated and UNSM-treated specimens at a normal load of 1 N which may be attributed to the modified surface layer at the top surface having higher hardness and smoother roughness with a small number of porosity, respectively. This reduction in friction coefficient enables to reduce energy consumption of water-based tribological systems. Wear track analysis was conducted using a nanoscale hybrid microscopy (NHM). NHM images showed that severe polishing and grooving marks were observed on the untreated specimen, while only mild grooving marks were observed on the UNSM-treated specimen. It was also confirmed that the UNSM technique changes the wear mechanisms of SiC: oxidative-adhesive-abrasive-micro fracture wear takes place in the untreated specimen, while adhesive-abrasive wear takes place in the UNSM-treated specimen. Application of UNSM technique would be highly advantageous for water-lubricated ceramic bearings.

The effects of AlCrN coating, surface modification and their combination on the tribological properties of high speed steel under dry conditions

In this study, the effects of a combination of ultrasonic nanocrystalline surface modification (UNSM) technique and AlCrN coating on the tribological properties of high speed steel (HSS) were investigated. The AlCrN coating with a thickness of about 3µm was deposited by the physical vapor deposition (PVD) technique onto the polished and UNSM-treated HSS specimens. The tribological and scratch tests results revealed that the AlCrN coating deposited onto the UNSM-treated specimen showed better tribological properties compared to that of the AlCrN coating deposited onto the polished specimen, which may be attributed to the modified surface beneath the AlCrN coating. Hence, it is expected that the results of this study can be applied to reduce the wear of fine blanking punches.

The usability and preliminary effectiveness of ultrasonic nanocrystalline surface modification technique on surface properties of silicon carbide

Abstract This study reports the change in microstructural, mechanical and tribological characteristics of sintered silicon carbide (SiC) ceramic subjected to ultrasonic nanocrystalline surface modification (UNSM) technique. The surface microstructure of the untreated and UNSM-treated specimens was examined by SEM, EDS and XRD. The mechanical properties of the specimens were measured by nanoindentation. The tribological properties of the specimens were assessed using a ball-on-disk tribometer against a bearing steel (SAE52100) ball at two different temperatures under dry reciprocating conditions. It was confirmed by SEM that the UNSM-treated specimens had much denser microstructure than those of the untreated specimens. The EDS results revealed that the UNSM technique has no effect on the chemical composition of sintered SiC ceramic. The average surface roughness obtained by AFM was found to be about 83.6 nm and 60.1 nm for the untreated and UNSM-treated specimens, respectively. The tribological results showed that the UNSM-treated specimens exhibited a lower friction coefficient and higher wear resistance compared to those of the untreated specimens. In addition, it was found that the UNSM technique was able to decrease the quantity of pores. The results of this study are expected to make sintered SiC ceramic more attractive for numerous applications in various industries.

Enhancement in wear resistance of sintered silicon carbide at various temperatures

In this study, the mechanical and tribological properties of sintered silicon carbide (S-SiC) subjected to ultrasonic nanocrystalline surface modification (UNSM) technique were investigated. The tribological properties of the untreated and UNSM-treated specimens were assessed using a ball-on-disk tribometer against an alumina (Al2O3) ball at various temperatures under oil-lubricated conditions. The results indicated that the UNSM-treated specimen exhibited better tribological properties compared to that of the untreated specimen. Scratch tests were also performed on these specimens. The surface roughness obtained using an atomic force microscope (AFM) was found to be 101.7nm and 81.9nm for the untreated and UNSM-treated specimens, respectively. It was also found that the UNSM technique was beneficial for a decrease in quantity of pores.

Fatigue behaviour of Ti-6Al-4V alloy under combined low and high cycle and ultrasonic loading

The importance of the fatigue behaviour of Ti-6Al-4V alloys aerospace parts at low and high cycles has gained strength in last decades due to their long service life. In this study, an ultrasonic nanocrystalline surface modification (UNSM treatment was performed on a Ti-6Al-4V alloy in order to extend the fatigue behaviour using a hydraulic and ultrasonic fatigue testing (UFT systems. The fatigue enhancement mechanism of Ti-6Al-4V alloy was discussed on the residual stress and S-N behaviour with X-ray diffraction results. High-cycle fatigue behaviour of Ti-6Al-4V alloy was studied up to 107–109 using a piezoelectric ultrasonic fatigue tester operating at 20 kHz. The high-cycle fatigue results showed that the UNSM-treated specimen had better performances. Failure in the Ti-6Al-4V alloy was observed around the gigacycle regime with the fractures being found to initiate from the surface. The fracture surfaces exhibit brittle characteristics containing river patterns and cleavage facets, as well as striations.