• Title/Summary/Keyword: ultrasonic nano-crystal surface modification

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A Study on the Ultrasonic Nano Crystal Surface Modification(UNSM) Technology and It's Application (초음파 나노표면개질기술의 특성과 활용방안 연구)

  • Pyoun, Young-Sik;Park, Jeong-Hyeon;Cho, In-Ho;Kim, Chang-Sik;Suh, Chang-Min
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.3
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    • pp.190-195
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    • 2009
  • All the failure in fatigue of torsion, bending and rolling contact, and in sliding wear begins mostly from surface. So much efforts have been invested to the surface technology which deal these problems during past decades, but the industrial demand keeps growing and more significant requirements are added to researchers and engineers. Nano crystal surface modification technology which makes the surface layers into nano crystalline, induces big and deep compressive residual stress, increases surface hardness, improves surface hardness, and make micro dimples structure on surface is an emerging technology which can break limits of current surface technology and relieve the burden of researchers and engineers. In this study, a nano crystal surface modification technology which is calling UNSM(Ultrasonic nano crystal surface modification) technology, is introduced and how it has been applied to industry to solve these failure problems is explained.

The effect of ultrasonic nano crystal surface modification for mitigation of the residual stress after weld inlay on the alloy 82/182 dissimilar metal welds of reactor vessel in/outlet nozzles (원자로 입출구 노즐 Alloy 82/182 이종금속 용접부 Weld Inlay 적용 후 초음파나노표면개질이 잔류응력 완화에 미치는 영향)

  • Cho, Hong Seok;Park, Ik Keun;Jung, Kwang Woon
    • Journal of Welding and Joining
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    • v.33 no.2
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    • pp.40-46
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    • 2015
  • This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

Intergranular Corrosion of 316L Stainless Steel by Aging and UNSM (Ultrasonic Nano-crystal Surface Modification) treatment (시효열처리 및 UNSM 처리에 따른 316L 스테인리스강의 입계부식거동)

  • Lee, J.H.;Kim, Y.S.
    • Corrosion Science and Technology
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    • v.14 no.6
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    • pp.313-324
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    • 2015
  • Austenitic stainless steels have been widely used in many engineering fields because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion, stress corrosion cracking, pitting, etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled using methods such as lowering the carbon content, solution heat treatment, alloying of stabilization elements, and grain boundary engineering. This work focused on the effects of aging and UNSM (Ultrasonic Nano-crystal Surface Modification) on the intergranular corrosion of commercial 316L stainless steel and the results are discussed on the basis of the sensitization by chromium carbide formation and carbon segregation, residual stress, grain refinement, and grain boundary engineering.

Friction characteristics of SUS 304 and SUS 630 stainless steel in Dry, Grease-, and Oillubricated conditions and wear property in dry condition before and after Ultrasonic Nano-crystal Surface Modification (SUS 304과 SUS 630 소재의 UNSM(초음파나노 표면개질) 처리전후 Dry, Grease윤활, Oil윤활 상태하에서 마찰특성 및 Dry 상태하에서 마모특성)

  • Kim, J.H.;Pyoun, Y.S.;Park, J.H.;Choi, G.S.;Amanov, Auezhan
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2010.05a
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    • pp.521-522
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    • 2010
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Study on the Drag Reduction of 2-D Dimpled-Plates (딤플을 적용한 평판에 대한 항력 감소 연구)

  • Paik, Bu-Geun;Pyun, Young-Sik;Kim, Jun-Hyung;Kim, Kyung-Youl;Kim, Ki-Sup;Jung, Chul-Min;Kim, Chan-Ki
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.4
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    • pp.333-339
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    • 2012
  • The main objective of the present study is to investigate the roles of the micro-dimpled surface on the drag reduction. To investigate the effectiveness of the micro-dimpled surface, the flat plates are prepared. The micro-size dimples are directly carved on the metal surface by ultrasonic nano-crystal surface modification (UNSM) method. Momentum of the main flow is increased by the dimple patterns within the turbulent boundary layer (TBL), however, there is no significant change in the turbulence intensity in the TBL. The influence of dimple patterns is examined through the flow field survey near the flat plate trailing edge in terms of the profile drag. The wake flow velocities in the flat plate are measured by PIV technique. The maximum drag reduction rate is 4.6% at the Reynolds number of $10^6{\sim}10^7$. The dimples tend to increase the drag reduction rate consistently even at high Reynolds number range.

Effect of the Amplitude in Ultrasonic Nano-crystalline Surface Modification on the Corrosion Properties of Alloy 600

  • Kim, Ki Tae;Kim, Young Sik
    • Corrosion Science and Technology
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    • v.18 no.5
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    • pp.196-205
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    • 2019
  • Surface modification techniques are known to improve SCC by adding large compressive residual stresses to metal surfaces. This surface modification technology is attracting attention because it is an economical and practical technology compared to the maintenance method of existing nuclear power plants. Surface modification techniques include laser, water jet and ultrasonic peening, pinning and ultrasonic Nano-crystal surface modification (UNSM). The focus of this study was on the effect of ultrasonic amplitude in UNSM treatment on the corrosion properties of Alloy 600. A microstructure analysis was conducted using an optical microscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). A cyclic polarization test and AC-impedance measurement were both used to analyze the corrosion properties. UNSM treatment influences the corrosion resistance of Alloy 600 depending on its amplitude. Below the critical amplitude value, the pitting corrosion properties are improved by grain refinement and compressive residual stress, but above the critical amplitude value, crevices are formed by the formation of overlapped waves. These crevices act as corrosion initiators, reducing pitting corrosion resistance.

Rolling Contact Fatigue and Residual Stress Properties of SAE52100 Steel by Ultrasonic Nano-Crystalline Surface Modification (UNSM) (초음파 나노표면 개질처리를 통한 베어링강의 회전접촉피로 및 잔류응력 특성에 대한 연구)

  • Lee, Changsoon;Park, Ingyu;Cho, Insik;Hong, Junghwa;Jhee, Taegu;Pyoun, Youngsik
    • Journal of the Korean Society for Heat Treatment
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    • v.21 no.1
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    • pp.10-19
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    • 2008
  • To investigate the effect of ultrasonic nano-crystalline surface modification (UNSM) treatment on rolling contact fatigue and residual stress properties of bearing steels, this paper carried out a rolling contact fatigue test, measured residual stress and retained austenite, performed a wear test, observed microstructure, measured micro hardness, and analyzed surface topology. After the UNSM treatment, it was found that the surface became minute by over $100{\mu}m$. The micro surface hardness was changed from Hv730~740 of base material to Hv850~880 with about 20% improvement, and hardening depth was about 1.3 mm. The compressive residual stress was measured as high as -700~-900 MPa, and the quantity of retained austenite was reduced to 27% from 34%. The polymet RCF-6 ball type rolling contact fatigue test showed over 4 times longer fatigue lifetime after the UNSM treatment under 551 kgf load and 8,000 rpm. In addition, this paper observed the samples, which went through the rolling contact fatigue test, with OM and SEM, and it was found that the samples had a spalling phenomenon (the race way is decentralized) after the UNSM treatment. However, before the treatment, the samples had excessive spalling and complete exploration. Comparison of the test samples before and after the UNSM treatment showed a big difference in the fatigue lifetime, which seems to result from the complicated effects of micro particles, compressive residual stress, retained austenite, and surface topology.