• Journal of the Korean institute of surface engineering
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• v.43 no.5
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• pp.243-247
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• 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.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.42-47
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• 2000

The object of this study is to estimate Sn-Ag-Bi-Ga solder alloy as a substitute for Sn-37Pb alloy. For Sn-Ag-Bi-Ga alloys, Ag, Bi and Ga contents are varied. (Ag : 1~5%, Ga : 3%, Bi : 3~6%) Comparing to Sn-37Pb alloy Sn-Ag-Bi-Ga alloys have wider melting temperature range up to max. $18.7^{\circ}C$. With increasing Ag, Bi contents, the wettability of the alloys increased up to max. 6.6 mN. The vickers hardness of the alloys was max. 46.4 Hv. The ultimate tensile stress of the alloys was max. 60.3 MPa and the elongation was max. 1.2%. The joint strength between circuit board and solder was max. 55.5 N and the joint strength between connector and solder was max. 176.1 N. There were no cracks in this alloys after thermal shock test.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.61-65
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• 2001

The fracture toughness of ceramics can be measure by such various methods as DT (double torsion), CN (chevron notch) etc. But, the application of these methods to the engineering ceramics is very difficult because of its very high hardness. So, IF (indentation fracture) method is generally used for the evaluation of fracture toughness of ceramics. The Median crack induced by the sharp Vickers indenter was compared with the detected AE (acoustic emission) signal. On the silicon nitride ceramics, the AE test results agree fairly well with the median crack occurance and growth process. But, on the alumina, very many complicated crack signals were detected besides median crack. It can be considered that the IF methods must be used in limited engineering ceramics materials.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.2_2
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• pp.233-238
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• 2022

This study evaluated the fatigue limit depending on microcracks using 0.57 wt.% carbon steel with different Vickers hardness. The fatigue limit was almost constant up to a certain limit regardless of the carbon content. However, the fatigue limit decreased rapidly as the size of the crack increased. As the crack aspect ratio was smaller, the fatigue limit of the depth (point A) a lot decreased. The fatigue limit ratio of the depth decreased significantly because the crack propagation in the depth direction was fast as the crack aspect ratio became smaller. On the other hand, the fatigue limit ratio of surface cracks increased as the crack aspect ratio decreased.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.244-254
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• 2022

For tensile tests, Vickers hardness tests and microstructure tests, plate-type and box-type specimens of austenitic 316L stainless steels were produced by a conventional machining (CM) process as well as two additive manufacturing processes such as direct metal laser sintering (DMLS) and direct metal tooling (DMT). The specimens were irradiated up to a fast neutron fluence of 3.3 × 10⁹ n/cm² at a neutron irradiation facility. Mechanical performance of the unirradiated and irradiated specimens were investigated at room temperature and 300 ℃, respectively. The tensile strengths of the DMLS, DMT and CM 316L specimens are in descending order but the elongations are in reverse order, regardless of irradiation and temperature. The ratio of Vickers hardness to ultimate tensile strength was derived to be between 3.21 and 4.01. The additive manufacturing processes exhibit suitable mechanical performance, comparing the tensile strengths and elongations of the conventional machining process.

• Restorative Dentistry and Endodontics
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• v.38 no.1
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• pp.36-42
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• 2013

Objectives: This study evaluated the antibacterial effect and mechanical properties of composite resins ($L_{CR}$, $M_{CR}$, $H_{CR}$) incorporating chitosan with three different molecular weights (L, Low; M, Medium; H, High). Materials and Methods: Streptococcus (S). mutans 100 mL and each chitosan powder were inoculated in sterilized 10 mL Brain-Heart Infusion (BHI) solution, and was centrifuged for 12 hr. Absorbance of the supernatent was measured at $OD_{660}$ to estimate the antibacterial activities of chitosan. After S. mutans was inoculated in the disc shaped chitosan-containing composite resins, the disc was cleansed with BHI and diluted with serial dilution method. S. mutans was spread on Mitis-salivarius bacitracin agar. After then, colony forming unit (CFU) was measured to verify the inhibitory effect on S. mutans biofilm. To ascertain the effect on the mechanical properties of composite resin, 3-point bending and Vickers hardness tests were done after 1 and 3 wk water storage, respectively. Using 2-way analysis of variance (ANOVA) and Scheffe test, statistical analysis was done with 95% significance level. Results: All chitosan powder showed inhibition effect against S. mutans. CFU number in chitosan-containing composite resins was smaller than that of control resin without chitosan. The chitosan containing composite resins did not show any significant difference in flexural strength and Vickers hardness in comparison with the control resin. However, the composite resin, $M_{CR}$ showed a slightly decreased flexural strength and the maximum load than those of control and the other composite resins $H_{CR}$ and $L_{CR}$. Conclusions: $L_{CR}$ and $H_{CR}$ would be recommended as a feasible antibacterial restorative due to its antibacterial nature and mechanical properties.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1861-1868
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• 1992

Laser beam hardening of 12%-Cr steel has been evaluated by using a continuous wave 3kW co$_{2}$ laser with a hardening mirror set. Experiment was performed on the hardening condition with a laser power of 2.85kW and travel speed of 1.0 and 1.5m/min. Multi passes have been also tried to find the hardening characteristics of partly overlapped zone. The black paint to use at high temperature was adopted to increase the absorptivity of laser beam energy with the wavelength of 10.6.mu.m at the surface of base metal. The microstructure of the hardened layers was observed by using a light microscopy, SEM and TEM. A fine Lamellar martensite formed in the hardened zones exhibits very high Vickers microhardness of 600Hv, whereas the tempered martensite distributes in the base metal with Vickers microhardness of 240Hv.It has been found that laser hardening with multi passes showed no significant drop of the hardness between adjacent passes.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.4
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• pp.825-836
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• 1998

The intention of this study was to investigate the preventive effect of chlorhexidine varnish on enamel demineralization. The sample consisted of 57 first premolars scheduled to be extracted for orthodontic purposes. The control group (N=10) was left untreated and the experimental groups were worn with specially designed stainless steel orthodontic bands on premolar for plaque accumulation. The group 1 (N=9) was worn band only, the group 2 (N=19) was applied with chlorhexidine varnish for one time, and the group 3 (N=19) was applied with chlorhexidine varnish for 3 times once a week. After 4 weeks of experimental periods, every specimen were examined by SEM and Vickers hardness test to evaluate and compare the degree of enamel decalcification. The results were as follows: 1. Although SEM revealed various degree of enamel demineralization in every experimental groups, the group 1 showed more severe demineralizations than the group 2 and 3. 2. The mean Vickers Hardness Numbers measured in this study seemed to reveal that there was a statistically significant difference between the control goup and the group 1 (P<0.05), and also a significant difference between the group 1 and the group 2, 3 (P<0.05). And there was no significant difference between the group 2 and the group 3 (p>0.05). 3. The results of VHN did not deemed to show a statistically significant difference between maxillary premolar and mandibular premolar in both group 2 and group 3 (P>0.05).

• Laser Solutions
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• v.10 no.4
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• pp.13-17
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• 2007

Electron beam weldability was investigated for 1mm thick cold rolled sheets of commercially pure grade titanium and Ti-6Al-4V alloy. Accelerating voltage of 40kV, beam current of 6mA, and weld speed of 0.8m/min was used and focal position of focused electron beam was just on the surface of workpiece. Microstructure of weld metal, the heat affected zone and base metal was observed using optical microscope. Vickers hardness was measured across the welds and the transverse tensile test was carried out. Hydroformability test was also carried out for the butt welded coupons of commercially pure grade titanium. For the electron beam welded C P Ti, the average grain size was equiaxed $\alpha(15{\sim}25{\mu}m)$ for base metal, coarse equiaxed $\alpha(80{\sim}200{\mu}m)$ for weld metal and annealed and enlarged grain($40{\sim}120{\mu}m$) for the HAZ. The vickers hardness of C P Ti was $180{\sim}200Hv$ for base metal, and $160{\sim}180Hv$ for the weld metal and the HAZ. For the electron beam welded Ti-6Al-4V alloy, the vickers hardness was 360Hv for the base metal, abd $400{\sim}425Hv$ for the weld metal and the HAZ. All the failure occurred at the base metal, when the transverse weld tensile test was carried out for both electron beam welded C P Ti and Ti-6Al-4V alloy. The formability of electron beam welded C P Ti was decreased compared with that of C P Ti base alloy.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.2
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• pp.55-59
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• 2003

In this study, $Al_xTa_{1-x}$(x=0.0∼1.0) alloy thin films were grown by RF-Magnetron sputtering system, and the structural, mechanical and electrical properties of samples were examined by 4-point probe, XRD, AFM and micro-Vickers hardness profiler. The electrical resistivity was maximum and the crystal quality was optimum for the samples with Al content x=0.245 (Al 24.5 at.%). Regarding the surface hillock formation, the hillock density decreased with an increase of Al content for the low Al content range, and the hillock was eliminated for the sample with Al=24.5 at.%. The hillock density increased with the further increase of Al content. The high values of micro-Vickers hardness were obtained for the samples with x=0.2∼0.45. The results obtained demonstrate that the crystal quality, electrical resistivity, surface morphology and micro-hardness are closely inter-related, and that the optimum physical properties are obtained for the sample with x=0.245.