• Journal of Welding and Joining
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• v.28 no.3
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• pp.79-85
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• 2010

Hardfacing is one of the frequently applying method to increase surface hardness in hot forging die. Recently, hardfacing receives great attention due to it's repair availability and low cost. In hot forging die, crack resistance and thermal shock resistance have been considered as major properties, However there are few studies for the assessment of these properties. So, it is necessary to establish the assessment method for crack resistance and thermal shock resistance in hardfacing for hot forging die. In this study, flux cored arc welding was applied to make hardfacing welds. Three point bending test was carried out to assess hardfacing weld's crack resistance, and high temperature bending test using salt bath was developed for thermal shock resistance. Consequently, it was possible to assess crack resistance and thermal shock resistance of hardfacing welds for hot forging die quantitatively.

• Korean journal of food and cookery science
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• v.7 no.4
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• pp.71-86
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• 1991

This study was attempted to enhance nutritional value of cooked rice by adding milk in cooking water. Cooked and soaked rice with five different levels of milk in cooking water (0%, A: 30%, B: 50%, C: 70%, D: 100%, E) was tested for rheological parameters, fine structural changes, sensory evaluation. 1. Water absorbance of raw rice in cooking water with varying amountes of milk, was tested at $5^{\circ}C$ and $15^{\circ}C$ for 2 hours. Water absorption ratio was decreased as milk content was increased and soaking temperature was low. Time for maximum water absorption of sample A was 40 min at 1$15^{\circ}C$ but for sample B to D, it was not reached until 120 min. 2. Electronmicroscopic observation revealed that starch granules of rice lost their regular forms by soaking for 90 minutes, but recovered most of initial regularity after 24 hours. Increase in milk content of soaking water decreased marginal sharpness of the starch granule, presumably due to reduced swelling of the granule. 3. Degree of gelatinization of cooked rice was highest in sample A and progressively decreased as milk content was increased. It was, however, increased in all samples when the cooking water to rice ratio was raised from 160% to 180%. During 4 hour storage, rates of retrogradation were not different between A and B samples, but those of C, D and E were about 2.5 times higher than A and B under the optimal condition of 170% cooking water to rice ratio. This was in the order reverse to hardness order of AC>A, D＞E at cooking water to rice ratios of 160% and 170%, above which A sample surpassed the rest of samples. 4. Sensory evaluation conducted by fifteen university students as panelists showed that there were more significant differences among five samples in flavour, texture than appearance and a notable preference for b and C over A, D and E.

• Journal of Powder Materials
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• v.23 no.4
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• pp.282-286
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• 2016

A sintered body of $TiB_2$-reinforced iron matrix composite ($Fe-TiB_2$) is fabricated by pressureless-sintering of a mixture of titanium hydride ($TiH_2$) and iron boride (FeB) powders. The powder mixture is prepared in a planetary ball-mill at 700 rpm for 3 h and then pressurelessly sintered at 1300, 1350 and $1400^{\circ}C$ for 0-2 h. The optimal sintering temperature for high densities (above 95% relative density) is between 1350 and $1400^{\circ}C$, where the holding time can be varied from 0.25 to 2 h. A maximum relative density of 96.0% is obtained from the ($FeB+TiH_2$) powder compacts sintered at $1400^{\circ}C$ for 2 h. Sintered compacts have two main phases of Fe and $TiB_2$ along with traces of TiB, which seems to be formed through the reaction of TiB2 formed at lower temperatures during the heating stage with the excess Ti that is intentionally added to complete the reaction for $TiB_2$ formation. Nearly fully densified sintered compacts show a homogeneous microstructure composed of fine $TiB_2$ particulates with submicron sizes and an Fe-matrix. A maximum hardness of 71.2 HRC is obtained from the specimen sintered at $1400^{\circ}C$ for 0.5 h, which is nearly equivalent to the HRC of conventional WC-Co hardmetals containing 20 wt% Co.

• Korean Journal of Food Science and Technology
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• v.22 no.3
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• pp.266-271
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• 1990

Yukwa(Korean traditional puffed rice snack) puffed by vegetable oil was evaluated its shelf-life and monitored its physicochemical changes during long term storage. And air puffing instead of oil was tested for substitution of puffing medium. The shelf-life of oil puffed Yukwa was less than 4 weeks at $30^{\circ}C$ by peroxide value and negligible changes in physical texture was detected after 9 weeks storge. There was a possibility to apply air puffing method for Yukwa making and its optimum temperature was around $250^{\circ}C$. Air puffed Yukwa was a little less expansion rate, same level of hardness and high brittleness compared with oil puffed . Sensory evaluation of air puffed Yukwa was as same as air puffed in odour, firmness and texture but overall taste was less score probably causing by oil used which need a impovement for air puffed Yukwa. No differences in structure of both Yukwa observed by SEM was showed.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.444-449
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• 2010

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.

• Korean Journal of Materials Research
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• v.23 no.1
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• pp.18-23
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• 2013

In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at $470^{\circ}C$, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.

• Korean journal of food and cookery science
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• v.24 no.1
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• pp.31-38
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• 2008

Sulgidduk samples made with additions of 1, 2, 3, 4, and 5% Ulmus cortex powder, and a control, were examined for quality characteristics such as moisture content, color, gelatinization properties, textural characteristics, and consumer acceptance, in order to determine the optimal ratio of Ulmus cortex powder in the formulation. The moisture contents among the samples were not significantly different, ranging from 40.57 to 42.37%, and increased as the Ulmus cortex powder content increased. For the color values, lightness decreased and yellowness and redness increased with increasing Ulmus cortex powder content. With regard to the gelatinization properties, peak viscosity (P), trough viscosity (T), final viscosity (F), breakdown, and consistency increased with increasing amounts of Ulmus cortex powder. Pasting temperature, time to peak viscosity, and setback presented decreasing tendencies with the additions of Ulmus cortex powder. For the textural characteristics, increasing Ulmus cortex powder content presented decreases in hardness, springiness, and chewiness however, adhesiveness, cohesiveness, and gumminess were not significantly different among samples. In the consumer acceptance test, the scores of all evaluated characteristics decreased as the ratio of Ulmus cortex powder increased. However, the intensity ratings for the 1 and 2% Ulmus cortex powder samples showed the opposite effect, obtaining fairly good scores. In conclusion, the results indicate that adding $1{\sim}2%$ Ulmus cortex powder to Sulgidduk is optimal, providing good physiological properties and reasonably high consumer acceptability.

• Korean journal of food and cookery science
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• v.24 no.1
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• pp.23-30
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• 2008

Sulgidduk samples made with additions of 2, 4, 6, 8, and 10% Houttuynia cordata Thunb. powder, and a control were examined for quality characteristics such as moisture content, water activity, color, gelatinization properties, textural characteristics, and sensory qualities in order to determine the optimal ratio of Houttuynia cordata Thunb. powder in the formulation. The moisture contents among the samples ranged from 41.98% to 44.97%, and increased as the content of Houttuynia cordata Thunb. powder increased. The water activities of the samples were not significantly different. As the Houttuynia cordata Thunb. powder content increased, the redness and yellowness of the samples also increased, but lightness decreased. For the gelatinization properties, the additions of Houttuynia cordata Thunb. powder caused decreases in peak viscosity (P) and holding strength viscosity (H). Furthermore, final viscosity (F), setback, and time to peak viscosity decreased with increasing Houttuynia cordata Thunb. powder content; however, breakdown and temperature to peak viscosity were not significantly different among the samples. Hardness and gumminess decreased with increasing Houttuynia cordata Thunb. powder content, and adhesiveness, cohesiveness, chewiness, and resilience also tended to decrease; however, springiness was not significantly different among the samples. In the consumer acceptance test, as the content of Houttuynia cordata Thunb. powder increased, the scores of all evaluated characteristics decreased; while the characteristic intensity ratings showed the reverse effect, and the 2 and 4% Houttuynia cordata Thunb. powder samples obtained fairly good scores. In conclusion, the results indicate that adding $2{\sim}4%$ Houttuynia cordata Thunb. powder to Sulgidduk is optimal, providing good physiological properties and reasonably high overall consumer acceptability.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.315-321
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• 2015

Rare-earth zirconates, such as $La_2Zr_2O_7$ and $Gd_2Zr_2O_7$, have been investigated as one of the candidates for replacing conventional yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications at higher turbine inlet temperatures. In this study, double-ceramic-layer (DCL) TBCs of YSZ 1st layer and $La_2Zr_2O_7$ top coat layer are fabricated by suspension plasma spray with serial liquid feeders. Microstructures, hardness profiles, and thermal durability of DCL-TBCs are also characterized. Fabricated DCL-TBCs of YSZ/$La_2Zr_2O_7$ exhibit excellent properties, such as adhesion strength (>25 MPa) and electrical thermal fatigue (~1429 cycles), which are comparable with TBCs fabricated by atmospheric plasma spray.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.1121-1126
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• 2010

Borosilicate glass (81% $SiO_2$-2% $Al_2O_3$-13% $B_2O_3$-4% $Na_2O_3$) was prepared, and the glass was ion exchanged in $KNO_3$ powder containing different temperature and time. The $K^+-Na^+$ ion exchange takes place at the glass surface and creates compressed stress, which raise the mechanical strength of the glass. The depth profile of $Na^+$ and $K^+$ was observed by electron probe micro analyzer. With the increasing heat-treatment time from 0min to 20min, the depth profile was increased from 17.1um to 29.4um, but mechanical properties were decreased. It was also found out that excessive heat treatment brings stress relaxation. The Vickers hardness, Fracture Toughness and bending strength of ion exchanged samples at $570^{\circ}C$ for 10min were $821.8H_v$, $1.3404MPa{\cdot}m^{1/2}$, and 953MPa, which is about 120%, 180%, and 450% higher than parent borosilicate glass, respectively. Transmittance was analyzed by UV-VIS-NIR spectrophotometer. Transmittance of ion exchanged borosilicate glass was decreased slightly at visible-range. It can be expected that transparent bulletproof materials in more light-weight and thinner by ion exchanged borosilicate glass.