Jun Hyong Kim

Friction and Wear Characteristics of SUS304 and SUS630 after Ultrasonic Nanocrystal Surface Modification

Owing to the superior properties of stainless steel it is pertinent to make use of it in various applications of automotive, aerospace, nuclear, chemical and cryogenic products. This paper describes a study of friction characteristics of SUS304 and SUS630 stainless steel disk specimens against silicon nitride Si3N4 ball in dry, grease-, and oil-lubricated conditions and wear characteristics in dry condition in sliding contact. The ultrasonic nanocrystal surface modification (UNSM) technology was applied to those disk specimens and its friction and wear properties were compared with polished one. The experiment was conducted with a pin-on-disk tribo tester using ball-on-disk contact geometry at room temperature. The experiment results show that in dry, greased- and oil-lubrication conditions the coefficient of friction of UNSM-treated specimens was lower and constant than polished specimens and in dry condition the wear rate was also smaller than polished one. Micro dimples made by UNSM treatment contribute those effects.

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).

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.

The Effects of Ultrasonic Nanocrystal Surface Modification Technique Temperature on Microstructure and Wear of Alloy 600

Alloy 600 (UNS N06600) is an austenitic nickel-based alloy with superior corrosion resistance and high-temperature endurance, which determines its widespread applications in aeronautical, aerospace, marine and nuclear industries. Particularly, a number of nuclear components used Alloy 600 as their structure materials due to their high corrosion resistance, high-temperature endurance and excellent fabricant characteristics. Many failures have occurred in Alloy 600 with various forms of environmental degradations during long-term operation. In this study, an ultrasonic nanocrystal surface modification (UNSM) technique was applied to Alloy 600 at a room and a high temperature of 500 OC. The effects of UNSM treatment temperature on the microstructure and wear behavior including a compressive residual stress were investigated. The hardness, compressive residual stress with respect to depth from the top surface were measured. Also, the wear behavior of UNSM-treated at a room and a high temperature Alloy 600 specimen was compared to that of the untreated specimen. The increase in wear resistance by UNSM technique was discussed in terms of increased hardness, refined grain size and induced compressive residual stress.

Stability Enhancement for Cold Field Emitter for Reliable Operation of the Micro-Column System

Recently, the micro-column has been intensively studied as a potential candidate for next-generation lithography with high-throughput capability. The micro-column has a simple structure with an electron emitter, micro-lenses, a double octupole deflector, and an Einzel lens. The structure and performance of the micro-column are dependent on the characteristics of the electron emitter. The electron emitter should have several prerequisites such as stable emission of electrons, high brightness and long lifetime. It is also necessary for the emitted electrons to have sufficiently low kinetic energy, which can be achieved by using a very sharp emission tip. In this work, we made an extremely sharp tip by electro-chemically etching the tungsten wire in 10 % KOH solution. From the Fowler-Nordheim plot, the effective radius of the tip was found to be as small as ~12 nm, which is consistent with the value measured by SEM. We also discovered that the stability of emission can be enhanced very much through thermal treatment of the tip end by irradiating the Nd:YAG laser pulse