In-Gyu Park

TRIBOLOGICAL CHARACTERISTICS OF RADIAL JOURNAL BEARINGS BY ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION TECHNOLOGY

Ultrasonic nanocrystal surface modification (UNSM) has applied to a radial journal bearings made of bearing steel SUJ2. Mechanical characteristics are compared between UNSM treated and untreated bearings. Friction torque is measured at the boundary lubrication condition, the mixed lubrication condition, and the full hydrodynamic lubrication condition. The peak torque at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM treated samples are reduced. These effects are very useful to improve the service life of journal bearings. The Stribeck curve at the mixed and full hydrodynamic lubrication is derived and compared. The friction coefficient at these two regimes is reduced by more than 50%, which will do effective role for improvement of energy efficiency. The major effects for this reduction at three lubrication regimes could be explained in the terms of micro dimple surface.

Caustic stress corrosion cracking of alloys 600 and 690 with NaOH concentrations

In order to evaluate the stress corrosion cracking resistance for commercial alloys (C600MA, C600TT, C690TT) and Korean-made alloys (K600MA, K690TT), C-ring tests were performed in a caustic environment of 4, 10, 20, 30, and 50% NaOH solution at 315°C, for 480 h with an applied potential of 125 mV vs. OCP. Different stress corrosion cracking phenomena were observed according to the NaOH concentration. The rate of caustic IGSCC attack did not appear to increase monotonically with caustic concentrations, but peaked at a concentration between 4 and 50% caustic, or approximately 30% NaOH. Intergranular stress corrosion cracking was found for C600MA in 10, 20, and 30% NaOH solutions, while no cracking was observed in the 4 and 50% NaOH solutions. In 30% NaOH solution, transgrnular stress corrosion cracking was detected in C690TT, which may be related with the large amount of plastic strain (150% yield) and the applied potential (125 mV vs. OCP). The overall data clearly indicate that C600MA has the worst SCC resistance while K690TT offers the best resistance. There is also fairly good correlation between the caustic SCC susceptibility and some metallurgical parameters, particularly the grain size and the yield strength at room temperature. Specifically, materials having larger grain size and lower yield strength exhibited higher caustic SCC resistance.

ROLLING CONTACT FATIGUE CHARACTERISTICS OF SAE52100 BY ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION TECHNOLOGY

UNSM(Ultrasonic Nanocrystal Surface Modification) technology has been applied to test specimens of bearing rings and rollers made of SAE52100. Mechanical properties, especially rolling contact fatigue characteristics, are analyzed using two-roller test and 6-ball test before and after UNSM treatment. The main effects to improve rolling contact fatigue characteristics by UNSM treatment are explained in the view points of residual stress, hardness and surface topology.

Applied Cases and Application Technologies of Ultrasonic Nanocrystalline Surface Modification and Accelerated Fatigue Life Evaluation Using Ultrasonic Elastic Vibrational Energy

Key Words : Ultrasonic Nanocrystalline Surface Modification( ), Ultr초음파나노표면개질 asonic Fatigue Test( 초음파피로시험), Accelerated Testing( )가속시험초록: 최근플랜트산업분야에서는발전설비와해양플랜트및선박 교량건설등핵심구조물들에대한,내구성향상및평가를위한기술이크게확장적용될것으로본다 이에본연구에서는초음파탄성진.동에너지를이용한초음파나노표면개질(Ultrasonic Nanocrystalline Surface Modification) 기술과초음파피로시험 기술을통해서현재까지국내산업분야에서활발하게진행중인적용사례를(Ultrasonic Fatigue Test)분석하고자하였으며 플랜트분야특히발전설비와해양선박플랜트및교량건설구조물들의핵심용접.부에대한내구성향상을위해크게확장적용될수있는새로운응용기술연구방향에대한방법들을제시하고자한다.Abstract : It is greatly expected that the technologies of durability enhancement and evaluation for the corestructures of plant facilities, marine plant and bridge constructures will be greatly expanded in the plantindustry fields. In this study, the actively ongoing applied cases were tried to be analyzed in the presentdomestic industry fields through the Ultrasonic Nanocrystalline Surface Modification (UNSM) and UltrasonicFatigue Test (UFT) technologies using ultrasonic elastic vibrational energy, and the new applicationtechnology to improve the durability of plant industry field, especially plant facilities, marine plant and coreweld components of bridge constructures will be presented.

Carbon migration in a bearing steel with spheroidal cementite subjected to ultrasonic nanocrystalline surface modification

This paper deals with bearing steel with spheroidal cementite dispersed in a ferrite matrix subjected to ultrasonic nanocrystalline surface modification (UNSM) treatment. Carbon migration microstructure development, including grain size refinement and dissolution of cementite, was studied utilizing electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Accumulated multiple gliding progressively refines cementite into nano-sized cementite particles mixed within ferrite nano-grains in the top surface layer. A decreasing volume fraction of cementite is observed with increasing depth in the top deformed layer, indicative of dissolution of cementite induced by plastic deformation.

Effects of ultrasonic nanocrystalline surface modification on the high-frequency fretting wear of CP titanium and Ti-6Al-4V alloy

The probability of encountering fretting in machines and engineering structures is extremely high, and it is well known that titanium alloys have poor fretting wear resistance. Titanium specimens which are made of commercially pure titanium (CP Ti) and Ti-6Al-4V alloy were treated by ultrasonic nanocrystalline surface modification (UNSM) treatment in order to strengthen fretting wear resistance. Lubricated high-frequency fretting wear tests were performed with a nanocrytalline twin system surface layer of both CP Ti and Ti-6Al-4V alloy fabricated by means of UNSM treatment, in comparison with untreated surface specimens. Knowing the corresponding loads and constant displacement that induce mixed fretting conditions will allow for the predetermination of wear regime. The fretting tests have been carried out on both CP Ti and Ti-6Al-4V alloy under normal loads in the range from 10 to 80 N, displacement amplitude of 30 µm and high-frequency of 20 kHz.