• 한국생산제조학회지
• /
• 제21권6호
• /
• pp.932-937
• /
• 2012

In the presented study, SM45C carbon steel parts were joined by friction welding. The welding process was carried out under optimized conditions using statistical approach. The study of SM45C is conducted with various combinations of process parameters. Parameter optimization, microstructure and mechanical property correlation are the major contribution of the study. The welded joints were produced by varying spindle revolution speed, friction pressure, upset pressure and burn-off length. Tension tests were applied to welded parts to obtain the strength of the joints. Fracturs properties were additionally obtained experimentally under fluctuated tensile loads. Microstructures using microphotographs were examined in the weld interface and weld region and heat affected zone and base metal and flash zone of welded parts. Finally, Hardness variations in welding zone and base metal were also obtained. Through these tests, the optimum conditions of parameters for ${\phi}20$ SM45C in friction welding were obtained when the friction spindle revolution was 1,950 rpm, the friction pressures was 30 MPs, upset pressures was 50 MPs.

• 소성∙가공
• /
• 제17권1호
• /
• pp.13-18
• /
• 2008

Mg and Mg alloys are promising materials for light weight high strength applications. In this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance the mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing(ECAP) at various processing temperatures were investigated experimentally. ECAP with channel angle of $90^{\circ}$ and corner angle of $0^{\circ}$ was successful at $300^{\circ}C$ without fracture of the samples during the processing. The hardness of the ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of temperature on the hardness and microstructure of the ECAP processed Mg were explained by the dislocation glide in the basal plane and non-basal slip systems and by the dynamic recrystallization and recovery.

• Journal of Welding and Joining
• /
• 제31권5호
• /
• pp.26-34
• /
• 2013

Boiler equipment in power plant is always being operated in harsh conditions and severely exposed to the extreme environment of high temperature. Therefore periodically the state of devices should be checked, diagnosed, and analyzed to ensure the reliability of the equipment. Traditionally, such a diagnosis is based one or two physical properties of the sample taken from the equipment like hardness, microstructure, etc.. However, to enhance the confidence of the diagnosis, it is necessary to synthesize those properties together. This paper is to propose such a synthetic procedure for T23 which was developed to be used in $569^{\circ}C/596^{\circ}C$ condition. Creep test and accelerated degradation test were performed simultaneously, and the physical properties such as microstructure, tensile strength, yield strength, hardness, and indentation properties were measured. This paper proposes a method of determining the remaining life by quantitative comparison. It will provide the basis of evaluating life assessment more objective and reliable.

• 열처리공학회지
• /
• 제24권5호
• /
• pp.277-286
• /
• 2011

The spot weldability of metal joints between SD35 and SD30A steel was investigated. This study was aimed to determine the spot welding parameters (i.e. welding current and time) for reinforcement bar joint and to evaluate the weldability, mechanical strength, hardness and microstructure. The results indicated that shear strength and elongation of the welding joints at 12.5kA and 1000 ms were 26.7 $kgf/mm^2$ and 22%, respectively. And fracture distribution of them by using shear and tensile test showed 100% necking mode and 100% ductile mode, respectively.

• 한국세라믹학회지
• /
• 제32권7호
• /
• pp.809-816
• /
• 1995

Ti1-xAlxN films were successfully deposited on high speed steel and silicon wafer by plasma-assisted chemical vapor deposition using a TiCl4/AlCl3/N2/Ar/H2 gas mixture. Plasma process enabled N2 gas to nitride AlCl3, which is not possible in sense of thermodynamics. XPS analyses revealed that the deposited layer contained Al-N bond as well as Ti-N bond. Ti1-xAlxN films were polycrystalline and had single phase, B1-NaCl structure of TiN. Interplanar distance, d200, of (200) crystal plane of Ti1-xAlxN was, however, decreased with Al content, x. Al incorporation into TiN caused the grain size to be finer and changed strong (200) preferred orientation of TiN to random oriented microstructure. Those microstructural changes with Al addition resulted in the increase of micro-hardness of Ti1-xAlxN film up to 2800Kg/$\textrm{mm}^2$ compared with 1400Kg/$\textrm{mm}^2$ of TiN.

• 한국세라믹학회지
• /
• 제31권3호
• /
• pp.321-329
• /
• 1994

Functionally gradient materials(FGM), which have the continuous or stepwise variation in a composition and microstructure, are being noticed as the material that solves problems caused by heterogeneous interface of coating or joining. And these materials also expect new functions occured by gradient composition itself. Therefore, to examine possibility of thermal barrier materials, TZP/Mo·FGM and TZP/Ni·FGM were fabricated by sintering method. As to the sintered specimens, sintering shrinkage, relative density and Vicker's hardness in each composition were examined. The phenomena due to the difference of sintering shrinkage velocity during sintering process and the thermal stress induced through differences of thermal expansion coefficient in FGM were discussed. And the structure changes at interface and microsturcture of FGM were investigated. As a results, the difference of shrinkage between ceramic and metal was about 14% in TZP/Mo and 7% in TZP/Ni. The relative density and hardness were considerably influenced by metal content changes. Owing to unbalance of sintering shrinkage velocity between ceramic and metal, various sintering defects were occured. To control these sintering defects and thermal stress, gradient composition of FGM should be narrow. The microstructure changes of FGM depended on the ceramic or metal volume percents and were analogous to the theoretical design.

• Journal of Welding and Joining
• /
• 제16권2호
• /
• pp.84-92
• /
• 1998

On this study, the variations of hardness and microstructure were observed at he spot-welded part of 5182 alminum alloy sheets with thickness of 1.2 mm. The hardness of spot-welded part of aluminum alloy indicated the lowest value at nugget center. Also, the position where fatigue crack exists was investigated by surveying microstructure of the spot-welded sections. Mean load-deformation diagrams were obtained from static tensile test. Fracture was occurred completely within 5 mm after transforming elastic into plastic area. Fatigue test was stopped when the specimens of fatigue test had the final displacement of 0.2mm and measured fatigue bending angle and crack length. This study utilized them, investigated the relations between fatigue bending angle and fatigue crack length and made a estimation of the fatigue fracture life of resistance spot welded part of 5182 aluminum alloy sheet. The relative equation o fatigue crack length and fatigue failure life can be represented by {TEX}$L_{C}${/TEX}=α{TEX}$N_{f}^ {β}${/TEX}.

• 한국식품조리과학회지
• /
• 제6권3호통권12호
• /
• pp.33-41
• /
• 1990

This study was conducted to compare the characteristics of the ordinary soybean curd and 3 protein-adding soybean curds (soy protein, casein, gelatin). The sensory evaluation, textural analysis by Instron Universal Testing Machine & the microstructure analysis by SEM for 4 soybean curds were carried out. The results were as follows: 1. In sensory evaluation. 1) The differentiation of soybean curds was greatly explained by `hardness in mouth' through ANOVA test. 2) Discriminant analysis showed that the properties of casein soybean curd were different from those of other three soybean curds by discriminant function I, and the properties of soy protein soybean curd were slightly different from those of ordinary and gelatin soybean curds by discriminant function II. 2. In textural analysis by Instron, protein-adding soybean curds showed significantly lower hardness than ordinary soybean curd. 3. In microstructure analysis by SEM, soy protein soybean curd showed regular, good honeycomb-like network structure and other soybean curds showed lumpy network. The structure of gelatin soybean curd was slightly similar to that of ordinary soybean curd.

• Journal of Welding and Joining
• /
• 제34권6호
• /
• pp.69-74
• /
• 2016

Because the pure titanium has superior corrosion resistance and formability compared with different material, it is widely used as material of welded heat exchanger. When the welding of heat exchanger is carried out, certain area in which welding start and end are overlapped occurs. The humping of back bead is formed in the overlap area due to partial penetration. Thus in this study, the experiments were carried out by changing the length and wave shape of overlap area, and then the weldabiliay was evaluated through the observation of microstructure, the measurement of hardness and tensile-shear strength test in the overlap area. When overlap length was 9.8mm, humping bead was suppressed. The microstructure of overlap area coarsened and its hardness increased due to remelting. As a result of tensile-shear strength test in the overlap area according to applying the wave shape control, it was confirmed that the overlap area applied wave shape control had more excellent yield strength and ductility.

• 대한치과교정학회지
• /
• 제15권2호
• /
• pp.261-269
• /
• 1985

The purpose of this study was to measure and compare tensile strength for 3 types of new direct-bond brackets and the same brackets after recycling and to evaluate recycled brackets to determine the extent of physical alteration after recycling. Three types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile strength was measured by Universal Testing Machine. The brackets were recycled by thermal process and the tensile test was repeated. To determine the extent of physical alteration after recycling, the slot width and the hardness of metal brackets were measured and to analyze the microstructure of the brackets, photographs of the bracket microstructure were taken. Following results were obtained: 1. The tensile strength of recycled brackets was lower than that of new brackets, but there was no statistically significant difference. (p>0.05) 2. In the new and recycled brackets, the tensile strength of mini-mesh base bracket was statistically higher than that of conturlok base bracket, $(p\leq0.05)$ but there was no statistically significant difference between production of other companies. (p>0.05) 3. The slot width of metal bracket was enlarged from 0.459mm to 0.469mm as a result of the recycling process. (p>0.005) 4. As temperature was increased in thermal treatment, the grains of bracket metal gradually became coarser and the hardness was decreased.