• 소성∙가공
• /
• 제32권4호
• /
• pp.180-190
• /
• 2023

This study deals with residual stress prediction and hardness evaluation within cross ball grooved inner race fabricated by cold upsetting process consisted of upsetting and ejection steps. A raw workpiece material of AISI 5120H (SCr420H) is first spheroidized and annealed, then phosphophyllite coated to form solid lubricant layer on its outer surface. To investigate influences of the heat treatment, uni-axial compression tests and Vickers micro-hardness measurements are conducted. Three-dimensional elasto-plastic FE simulations on the upsetting step and the ejection one are performed to visualize the residual stress and the ductile (plastic deformation) damage. External feature of the fabricated inner race is fully captured by using an optical 3D scanner, and the micro-hardness is measured on internal cross-sections. Consequently, the dimensional compatibility between the simulated inner race and the fabricated one is ensured with a difference of under 0.243mm that satisfied permissible error range of ±0.50mm on the grooved surface, and the predicted residual stress is verified to have similar distribution tendency with the measured Vickers micro-hardness.

• Journal of Advanced Marine Engineering and Technology
• /
• 제23권6호
• /
• pp.806-813
• /
• 1999

The effect of Post-Weld Heat Treatment(PWHT) of SS400 Steel was investigated with parameters such as micro vickers hardness corrosion potential polarization behaviors galvanic current Al anode generating current Al anode weight loss etc. Hardness of each parts(HAZ, BM, WM)by PWHT is lower than that of each parts by Non Post-Weld Heat Treatment(NPWHT) However hardness of WM of HAZ part was the highest among those three parts and HAZ area were also acted as cathode without any case of heat treatment. Potential difference between each three parts by PWHT was also smaller compared to NPWHT. Therefore it is suggested that Corrosion resistance property is increased by PWHT. However both Al anode generating current and anode weight loss was also decreased by PWHT compared to NPWHT when SS400 steel is cathodically protected by Al anode.

• 한국생산제조학회지
• /
• 제24권6호
• /
• pp.647-652
• /
• 2015

A probe pin is a key component of LED inspection equipment. The probe pin makes contact with the LED electrodes and supplies an electric current. Because the mechanical and electrical homogeneity of the probe surface affects the service life and reliability, its characterization is essential. For this study, the hardness was measured using a micro-Vickers hardness test. Moreover, the thicknesses of the plating at different locations and the elemental compositions were examined using an FE-SEM. The uniformity of the plating was found to be acceptable because palladium was detected consistently throughout the tested domain. In addition, the hardness of the surface was determined to be higher than that of the typical palladium range, which is attributed to the use of undercoated nickel.

• 한국레이저가공학회지
• /
• 제15권3호
• /
• pp.11-15
• /
• 2012

The laser weld of AZ31 magnesium alloy was characterized with OM, EBSD and micros vickers hardness tester in experiment. EBSD analysis and micro-hardness measurements were carried out at the three regions (Equiaxed Zone, Columnar Dendrite Zone, Base Metal) of the welded AZ31Mg alloy sheets. The magnesium alloy show the rectangular shape bead in laser weld. EBSD analysis revealed that the three regions show the heterogeneous distribution of grain size and microtexture. Micro-hardness measurement also revealed that the heterogeneous distribution of microstructure contributed to the heterogeneous micro-hardness distribution in the three regions.

• 마이크로전자및패키징학회지
• /
• 제10권2호
• /
• pp.55-59
• /
• 2003

본 연구에서는 RF-Magnetron 스퍼터링 장치를 이용하여 $Al_xTa_{1-x}$(x=0.0∼1.0) 합금박막을 성장하였고, 4탐침법, XRD, AFM, micro-Vickers 미소경도계를 사용하여 시료의 구조적, 기계적, 전기적 특성을 분석하였다. Al조성 x=0.245(Al 24.5 at.%)에서 전기저항이 가장 높게 나타났고, 결정질이 가장 우수하였다. 표면 hillock에 있어서는 낮은 Al 조성영 역에서는 x가 증가할수록 hillock이 감소하다가, x=0.245에서 hillock이 완전히 배제되었고, 이후 x 증가에 따라 hillock 밀도가 다시 급격히 증가하였다. 미소경도의 경우, Al조성 x=0.2∼0.45의 영역에서 가장 높은 경도값이 측정되었다. 본 연구의 모든 결과를 종합적으로 고려할 때, $Al_xTa_{1-x}$ 합금박막의 결정질, 전기저항, 표면형상, 미소경도는 상호 밀접한 관계를 가지고 있었으며, Al 조성 x=0.245에서 가장 우수한 물리적 특성이 나타났다.

• Composites Research
• /
• 제32권3호
• /
• pp.141-147
• /
• 2019

In this study, micro-sized and nano-sized pure aluminum (Al) powders were compressed by unidirectional pressure at room temperature. Although neither type of Al bulk was heated, they had a high relative density and improved mechanical properties. The microstructural analysis showed a difference in the process of densification according to particle size, and the mechanical properties were measured by the Vickers hardness test and the nano indentation test. The Vickers hardness of micro Al and nano Al fabricated in this study was five to eight times that of ordinary Al. The grain refinement effect was considered to be one of the strengthening factors, and the Hall-Petch equation was introduced to analyze the improved hardness caused by grain size reduction. In addition, the effect of particle size and dispersion of aluminum oxide in the bulk were additionally considered. Based on these results, the present study facilitates the examination of the effect of particle size on the mechanical properties of compacted bulk fabricated by the powder metallurgy method and suggests the possible way to improve the mechanical properties of nano-crystalline powders.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2007년도 춘계학술대회 논문집
• /
• pp.639-640
• /
• 2007

• 한국기계가공학회지
• /
• 제3권1호
• /
• pp.45-51
• /
• 2004

In this paper, the relationship between the mechanical properties of alumina abrasives and grinding performance was investigated. Micro vickers hardness and fracture strength of all abrasives used in this study were measured. The grinding experiments were earned out with alumina grinding wheels made by various kinds of alumina abrasives including 32A, WA, ART, ALOMAX, and RA. The performance of such grinding wheel for grinding SKD11 was evaluated by specific grinding energy, grinding-ratio, and surface roughness. The grinding wheels composed by the harder abrasives and the lower fracture strength abrasives showed better grinding performance.

• 한국표면공학회지
• /
• 제43권5호
• /
• pp.243-247
• /
• 2010

The micro Vickers hardness and internal stress of Ni-Fe metal thin film synthesized by electrodeposition method at $25^{\circ}C$ were studied as a function of bath composition, and surface microstructure and atomic compositions of thin films were investigated by SEM and EDS. And the shape change of $200\;{\AA}$ Ni-Fe nanowires made using anodic aluminum oxide(AAO) templates by electrodeposition method were observed by SEM as a function of ultrasonic treatment time and bath composition. The Fe deposition contents on the substrate non-linearly increased with Fe ion concentration over total metal ion concentration. In case of low Fe contents film, the grain size is smaller and denser than high Fe contents deposited films, and the micro Vickers hardness increased with Fe contents of electrodeposited films. These results affected the shape change of nanowire after ultrasonic treatments.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
• /
• pp.175-177
• /
• 2012

A corrosion resistance and hard nitrocarburized layer was distinctly formed on 310 austenitic stainless steel substrate by DC plasma nitrocarburizing. Basically, 310L austenitic stainless steel has high chromium and nickel content which is applicable for high temperature applications. In this experiment, plasma nitrocarburizing was performed in a D.C. pulsed plasma ion nitriding system at different temperatures in $H_2-N_2-CH_4$ gas mixtures. After the experiment structural phases, micro-hardness and corrosion resistance were investigated by the optical microscopy, X-ray diffraction, scanning electron microscopy, micro-hardness testing and Potentiodynamic polarization tests. The hardness of the samples was measured by using a Vickers micro hardness tester with the load of 100 g. XRD indicated a single expanded austenite phase was formed at all treatment temperatures. Such a nitrogen and carbon supersaturated layer is precipitation free and possesses a high hardness and good corrosion resistance.