Ultrasonic Nanocrystal Surface Modification Technology Research Articles

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

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

Effect of surface engineering on wear and fatigue behavior of thermally sprayed SiC coating

The objective of this study is to investigate the effect of surface engineering technologies, namely, TSC (thermal spray ceramic) coating and UNSM (ultrasonic nanocrystal surface modification) technology on the wear and fatigue behavior of SiC coating. The effects of UNSM technology on microstructure, mechanical, wear, and fatigue properties were investigated. The UNSM-treated coating decreased the CoF (coefficient of friction) under both dry and non-dry conditions. The wear track morphology showed that the coating experienced abrasive wear in dry conditions. In contrast, in non-dry conditions, adhesive wear was a dominant mode. Moreover, the UNSM technology could extend the RBF (rotary bending fatigue) life of the as-sprayed SiC coating throughout the applied stress levels. It is expected that aerospace, nuclear, etc. industries may be benefited from the features of UNSM technology, such as an increase in hardness, residual stress, wear resistance, and fatigue properties of SiC coating.

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.

Improvement in frictional and fatigue performances of AISI 4150H steel by dual ultrasonic nanocrystal surface modification for ball screw applications

The importance of a newly developed dual UNSM (ultrasonic nanocrystal surface modification) technology on rolling friction (RF) and rotary bending fatigue (RBF) of a ball screw made of AISI 4150H steel was investigated. RF tests against AISI 52100 steel were performed under grease-lubricated conditions. The results revealed that the RF and RBF were improved after dual UNSM technology, where an improvement in surface integrity and an introduction of compressive residual stress played an influential role, respectively. Based on these results, it can be assured to achieve a smooth motion, a low noise, small torque fluctuations and an extended service life of ball screws.

Application of ultrasonic nanocrystal surface modification for improving surface profile of DEDed AISI 316L

This study investigated the effect of ultrasonic nanocrystal surface modification (UNSM) on the deteriorated surface of AISI 316L deposited using the direct energy deposition (DED) technology. After UNSM treatment, the coarse DEDed surface was fined, and a regular micro-surface profile was implemented. Compared to the case before UNSM treatment, the waviness and roughness of the surface after UNSM treatment decreased by up to 73.8 % and 86.2 %, respectively, and reduced further as the UNSM interval was decreased. Surface severe plastic deformation (S2PD) was induced in the dendrite structure of the UNSM-treated DEDed sample surface. The microstructure was deformed till a depth of up to 92.13 mm from the surface and was significantly affected by the interval. After UNSM treatment, the hardness improved by up to 71.5 % and gradually decreased from the surface to the inside; the hardness was improved by UNSM up to a maximum depth of 400 μm. Although the UNSM interval condition had a significant effect on the DEDed surface, it barely affected the relationship between the directions of DED deposition and UNSM treatment. This study confirmed that the UNSM technology can effectively improve a DEDed surface.

A Study on the Improvement of the Fatigue Life of Bearings by Ultrasonic Nanocrystal Surface Modification Technology

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings were investigated. The fatigue life of the untreated and UNSM-treated needle roller bearings was evaluated using a roller fatigue tester at various contact stress levels, under oil lubrication conditions. It was found that the fatigue life of the UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with the untreated one. The results of the surface roughness and surface hardness of the needle roller bearings before and after UNSM technology were compared and discussed in order to understand the role of UNSM technology in improving fatigue life. It was found that the application of UNSM technology to the needle roller bearings can improve their fatigue life by reducing the friction coefficient and increasing the wear resistance, which may be attributed to the reduction in surface roughness from 0.50 µm to 0.15 µm and also the increase in surface hardness from 58 HRC to 62 HRC.

Surface engineering-controlled tribological behavior and adhesion strength of Ni-Cr coating sprayed onto carburized AISI 4340 steel substrate

In this study, a nickel‑chromium (Ni-Cr) coating was sprayed onto carburized AISI 4340 (UNS G43400) steel substrate by high-velocity oxygen fuel (HVOF) method. As-sprayed Ni-Cr coating was subjected to ultrasonic nanocrystal surface modification (UNSM) technology to control the tribological performance and adhesion strength. The aim of the current study is to improve the durability of Ni-Cr coating by the application of UNSM technology. The UNSM technology reduced the surface roughness and increased the surface hardness of the as-sprayed coating by about 64 and 25% that were associated with the elimination of high peaks and valleys, filling up micro-pores, respectively, where the unfilled open-pores and micro-cracks may be found as a stress concentration cite to suppress a crack initiation and crack propagation and a less number of open-pores may hinder the initiation and propagation of micro-cracks. The evaluation of the tribological performance of Ni-Cr coatings was evaluated using a wear tester in dry conditions, while the adhesion strength was obtained using a progressive scratch tester. As a result, the friction coefficient of the as-sprayed coating was reduced from about 1.1 to 0.75, and the adhesion strength was increased from about 3.3 to 6.1 N by the application of UNSM technology. The reduction in surface roughness of the UNSM-treated coating can be considered as the main parameter that influences on the frictional behavior, while increase in surface hardness determines the wear resistance and adhesion strength. It was found that the UNSM technology improved the tribological performance and adhesion strength of the coating.

Metal embedding and ultrasonic nanocrystal surface modification technology for super wear-resistant mechanical parts

High wear resistance is required for various mechanical parts that are in frequent physical contact with other mechanical parts, especially in heavy equipment, railways, and vehicles. For this reason, we propose a new design approach where zones of frequent contact are carved out and high-strength metals are substituted to form embedded parts in the grooves via an additive metal layer deposition (AM) process. In this work, the base metal was a casting iron and the metallic powder used in the AM process was AISI-H13, which is an excellent wear-resistant metal. After embedding, an ultrasonic nanocrystal surface modification (UNSM) process is applied as a post-process to increase the resistance properties of the wear zone by compressive residual stress. This work experimentally confirms that the wear rate decreased by up to 98.78% compared to the original base material gray cast iron; the wear rate in the embedded zone was almost 0%. We believe that the proposed method can be utilized for industrial applications as a surface strengthening technology to realize super wear resistance.

FTS를 이용한 나노표면개질공정의 공정변화와 소재에 따른 표면특성

A treatment for improving the characteristics of a surface is very important in increasing the life of machine parts. Many studies have been carried out on the surface characteristics after such treatments. For enhanced eco-technology, an alternative to a conventional chemical surface treatment process is essential. Ultrasonic nano-crystal surface modification (UNSM) technology is a physical environmentally friendly surface treatment method. This technology was developed in domestic and currently being used. As the mechanism of UNSM technology, a ball tip attached to an ultrasonic vibration device strikes the metal surface at nearly 20,000 times per second. The resulting modified surface layer improves the surface characteristics. This paper describes a self-developed fast tool servo system applied to the UNSM process as a vibration module within a high-frequency bandwidth. After describing the surface modification process based on the material and process changes, the surface characteristics are compared.

Reducing production loss by prolonging service life of rolling mill shear pin with ultrasonic nanocrystal surface modification technology

Premature failure at the shear pin of stainless hot rolling mill caused by increasing productivity and fluctuation of roll torque raises significant downtime cost. To reduce downtime cost, UNSM (Ultrasonic Nanocrystal Surface Modification) treatment is applied to the neck groove of shear pin as the alternative to existing solutions. This treatment prevents premature failure, increases service life and reduces the number of replacements. Proper process variables of UNSM technology which give the strongest fatigue strength are determined by comparing with S-N curve of rotary bending test result. Surface roughness, hardness and compressive residual stress on three kinds of test specimens are analyzed together with SEM analysis of fracture surface. Real shear pins are produced by the property of highest fatigue strength and installed to the hot mill stand for validation. They come to pass as twice as the original operation cycle.

A study on the restoration method of friction, wear and fatigue performance of remanufactured crankshaft

Crankshaft translates reciprocating linear piston motion into rotation in internal combustion engine. So it receives complex combination of stresses. Therefore, crankshaft remanufacturing process is designed thoroughly with special attention to fatigue and tribological performance. Experimental study is carried out in order to show that UNSM (ultrasonic nanocrystal surface modification) technology which will be used as final surface treatment after 0.2 mm depth surface grinding, could restore original fatigue strength and tribological performance. Furthermore the feasibility steady to replace conventional overlay welding in crankshaft remanufacturing process by UNSM (ultrasonic nanocrystal surface modification) technology is carried out. Effects of UNSM technology are established through rotary bending test, rolling contact fatigue (RCF) test and wear simulation test. The test specimen used SCM435 material of crankshaft and commercial bush. The test result showed fatigue limit improved by 30% and RCF life increased by 40% for UNSM treated specimen. And friction coefficient decreased by 24% and wear amount decreased by 85%.

Restoration of Rolling-Contact-Fatigued Surfaces via Nanoskin Technology

Rolling contact fatigue (RCF) is known as the dominant factor determining the service life of bearing materials. In this work, the fatigue life of the typical bearing alloy was significantly improved by introducing a nanoskin layer on the surfaces of the test specimens. The nanoskin layer structure was obtained by means of the ultrasonic nanocrystal surface modification (UNSM) technology. The microstructure of the nanoskin was analyzed via scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscope (TEM). SUJ2 and SUJ3 bearings at different states of fatigue were subjected to UNSM treatment. For SUJ2 a rotary-bending fatigue (RBF) life average for three untreated specimens was chosen as 100% life, and then several untreated specimens were fatigued to 25%, 50% and 75% of life with subsequent UNSM treatment. This way used bearing conditions were simulated. The rotary-bending fatigue (RBF) tests of fatigue+UNSM SUJ2 specimens have shown 377-430% improvement of fatigue life, comparing to untreated specimens. For SUJ3 a RCF life untreated specimen was chosen as 100% life, and then several specimens were fatigued to approximately 100% of surface damage with subsequent UNSM treatment. Thus damaged surface conditions were simulated. The RCF tests of fatigue+UNSM SUJ3 specimens have shown 218% improvement of fatigue life, comparing to untreated specimens. This indicates the possibility of the restoration of the RCF life of bearing alloys by means of nanoskin treatment via UNSM technology.

FATIGUE PROPERTIES OF ALUMINUM ALLOY (A6061-T6) WITH ULTRASONIC NANO-CRYSTAL SURFACE MODIFICATION

The corrosion resistance of aluminum can be improved by adding alloy elements or using a surface heat treatment process. The machine quality can be confirmed by analyzing the surface roughness, the surface hardness and the residual stress. In this paper, the fatigue characteristics of A6061-T6 aluminum specimens were obtained and compared with those of the treated specimens with the UNSM (Ultrasonic Nano-Crystal Surface Modification) technology and the untreated ones by using a multi-spindle rotating bending fatigue testing machine. The fatigue crack initiation and fatigue lives of the treated specimens with the UNSM technology was delayed and extended by the UNSM effects that are the increase of surface hardness, and the reduction of the surface roughness.

A STUDY ON THE ALTERNATIVE TECHNOLOGY USING UNSM INSTEAD OF THE PRESETTING METHOD FOR TORSION BAR

The torsion bar must be changed periodically due to its lack of durability and a phenomenon related to stress relaxation. Therefore technical development regarding the torsion bar's durability is urgently needed. In order to improve the fatigue life and durability of the dynamic components, new surface treatment technology such as ultrasonic shot peening, deep rolling, laser shock peening, etc. are developing widely. In this study, Ultrasonic Nanocrystal Surface Modification (UNSM) technology is applied as an advanced one to replace the presetting method (PM). UNSM and PM technology also induced the compressive residual stress on the surface layer of the torsion bar, which is the main improvement factor of fatigue life. DIN17221 material as a new MIL specification of torsion bar and SCM440 (as an alternative one to a old MIL-DTL-62567C) were processed with the UNSM technology to obtain the basic data and compare it between two, and then torsion fatigue tests of two materials were carried out to obtain the characteristics of torsion fatigue in this study.