• 수산해양기술연구
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• 제31권3호
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• pp.279-286
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• 1995

As Al-Li based alloys are to find widespread use in aerospace and other structural applications in which their low-density high specific stiffness properties be exploited, their mechanical properties must adequately match those of the which they intended to replace. In order to develop these purposed, the precipitation behaviors of the rapidly solidified Al-Li-Ti alloys aged at various temperature were investigated. ${\delta}'$ phase precipitated homogeneously in the matrix during not only melt quenching but also aging at the aging temperature of $160^{\circ}C\;and\;210^{\circ}C$. The addition of the Ti in Al-Li alloy promoted the formation of $\delta$' phase. The addition of Ti on the ${\delta}'$ solvus line had a little effect over the thermodynamics ${\delta}'$ solvus line. The reason for these behavior was that the ${\delta}'$ phase was suppressed to precipitate as much as supercooling by melt quenching. The discontinuous precipitation reaction occurred by the preferential growth of ${\delta}'$ phase due to the migration of grain boundary provided the driving force dependent of solute concentration fluctuations.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.104-105
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• 2006

The low-cycle fatigue performance and fracture of the P/M Ti-Fe-Mo-Al-Nd Alloys after sintering and forging have been studied. The linear regression equation of low-cycle fatigue lifetime has been obtained; the fatigue performances are objected under two different conditions. The fatigue fracture surface is analyzed by SEM. The low-cycle fatigue behavior of the P/M titanium alloy has been discussed.

• 열처리공학회지
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• 제10권1호
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• pp.63-70
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• 1997

A study was performed to examine the aging behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry and transmission electron microscopy. DSC measurements were conducted over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $5^{\circ}C$/min. for the specimens aged at 130, 160, $190^{\circ}C$ and $220^{\circ}C$ for various times after solution treatment at $540^{\circ}C$ for 30 minutes. The peaks due to the formation of G.P.zone were not detected in the specimens aged at 130 and $160^{\circ}C$, but those at 190 and $220^{\circ}C$ appeared in DSC curves. The heat absorption due to the dissolution of ${\delta}^{\prime}$ phase was increased with increasing aging time at $130^{\circ}C$ aging. In contrast, those values for the specimens aged at 160 and $190^{\circ}C$ were initially increased and inversely decreased at the transition time of 72 and 1 hour, respectively. The heat evolution due to the formation of $T_1$ phase was nearly unchanged at $130^{\circ}C$ aging, but at $160^{\circ}C$ and $190^{\circ}C$ aging, drastically decreased after the transition time. It can be considered that the increase of $T_1$ phase results in the decrease of ${\delta}^{\prime}$ phase when aging time is longer than the transition time. The hardness of the specimen aged at $190^{\circ}C$ is initially higher compared with that at $160^{\circ}C$, however, the peak hardness shows the lower value than that at $160^{\circ}C$.

• Tribology and Lubricants
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• 제39권1호
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• pp.13-20
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• 2023

Large drill bits may face high hardness ore and high working pressure when working. To optimize the use effect of large drill bits and prolong the use time, it is necessary to add a layer of pressure-resistant, wear-resistant, and low-friction coating on the surface of the drill bit. In this study, CoCrNiAlTi high-entropy alloy coatings and CoCrNiAlTi (70 wt%)-TiC (30 wt%) composite coatings are successfully prepared on Q235 steel by plasma spraying. The CoCrNiAlTi (70 wt%)-TiC (30 wt%) coating consists of FCC solid solution and a small amount of TiC phase. The effect of TiC on the composition phase, microhardness, and elastic modulus of HEA coating is studied by X-ray diffractometer (XRD) and microhardness tester. The effect of TiC on the friction and wear properties of HEA coatings is investigated using a wear tester. By improving the process parameters, the metallurgical bonding between the coating and the substrate is well combined, and a coating without pores and cracks is obtained. The experimental results confirm that the microhardness, elastic modulus, and wear resistance of CoCrNiAlTi-TiC composite coating are better, and the friction coefficient is lower.

• 한국기계가공학회지
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• 제12권6호
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• pp.159-166
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• 2013

In order to develop the optimum shape of an MQL carbide end-mill suitable for high speed machining of wing ribs which are a detailed part of larger wing structures, using a new material Al-Li alloy, a new MQL carbide end-mill is created that has various quantities of holes, hole sizes, and hole locations. A theoretical machining graph is generated using the hammer test and FRF simulation, and a machining test is performed in order to verify the machining stability in the high speed machining area. The optimum configuration of the MQL carbide end-mill is also presented through comparing the chattering, machining noise and cutting conditions, including the maximum cutting depth, rpm, and feed rate per teeth, for each cutter.

• 한국재료학회지
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• 제14권7호
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• pp.489-493
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• 2004

The electrical property of MMC is essentially important to some applications such as power transmission lines and cables, electronic and electrical components as well as electromagnetic shielding equipments. The behavior of electrical resistivity of $SiC_{w}/Al$ alloy composites under as-extruded and annealed conditions has been investigated within the temperature range from room temperature to $450^{\circ}C$. It can be seen that within entire temperature range, the electrical resistivity of composites was higher than that of an unreinforced matrix alloy under the same condition of either as-extrusion or annealing. The temperature dependence of both exhibited positive incline like a typical metal. The variation of electrical resistivity of an unreinforced matrix alloy with temperature from ambient temperature to $450^{\circ}C$ was nearly monotonous, while those of composites increased monotonously at low temperature and rose to a high level after about $250^{\circ}C or 275^{\circ}C$. The difference of these temperature dependences on electrical resistivity can be interpreted as qualitatively the interfaces of $SiC_{w}$ fibers and matrix, where act as nucleation sites.

• Steel and Composite Structures
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• 제42권4호
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• pp.553-568
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• 2022

This paper explored the viability of utilising titanium alloy bolts in the construction industry through an experimental programme, where a total of sixty-six titanium alloy (Ti/6Al/4V) bolts were tested under axial tension, pure shear and combined tension and shear. In addition, a series of Charpy V-notch specimens machined from titanium alloy bolts, conventional high-strength steel bolts, austenitic and duplex stainless steel bolts were tested for impact toughness comparisons. The obtained experimental results demonstrated that the axial tensile and pure shear capacities of titanium alloy bolts can be reasonably estimated by the current design standards for steel structures (Eurocode 3, AS 4100 and AISC 360). However, under the combined tension and shear loading conditions, significant underestimation by Eurocode 3 and unsafe predictions through AS 4100 and AISC 360 indicate that proper modifications are necessary to facilitate the safe and economic use of titanium alloy bolts. In addition, numerical models were developed to calibrate the fracture parameters of the tested titanium alloy bolts. Furthermore, a design-based selection process of titanium alloy bolts in the structural applications was proposed, in which the ultimate strength, ductility performance and corrosion resistance (including galvanic corrosion) of titanium alloy bolts was mainly considered.

• 한국재료학회지
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• 제33권10호
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• pp.393-399
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• 2023

In this study, changes in the microstructure and mechanical properties of cast and extruded Al-2Li-1Ce alloy materials were investigated as the Mg content was varied. The density decreased to 2.485, 2.46 and 2.435 g/cm³ when the Mg content in the Al-2Li-1Ce alloy was increased to 2, 4 and 6 wt%, respectively. Intermetallic compounds of Al₁₁Ce₃ were observed in all alloys, while the β-phase of Al₃Mg₂ was observed in alloys containing 6 wt% of Mg. In the extruded material, with increasing Mg content the average grain size decreased to 84.8, 71.6 and 36.2 ㎛, and the fraction of high-angle grain boundaries (greater than 15°) increased to 82.8 %, 88.6 %, and 91.8 %, respectively. This occurred because the increased Mg content promotes dynamic recrystallization during hot extrusion. Tensile test results showed that as the Mg content increased, both the yield strength and tensile strength increased. The yield strength reached 86.1, 107.3, and 186.4 MPa, and the tensile strength reached 215.2, 285, and 360.5 MPa, respectively. However, it is worth noting that the ductility decreased to 27.78 %, 25.65 %, and 20.72 % as the Mg content increased. This reduction in ductility is attributed to the strengthening effect resulting from the increased amount of dissolved Mg, and grain refinement due to dynamic recrystallization.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.89-93
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• 1997

A superlastic material, aluminum - lithium alloy 8090, were examined with uniaxial tensile test to investigate its thermomechanical behavior. The tests were carried out at the strain-rates ranging from 2${\times}$10-4 to 1${\times}$10-2 and at the temperatures from 48 0$^{\circ}C$ to 540$^{\circ}C$. The experiments produced force-displacement curves which converted to stress-strain curves. From the curves, several important superplastic factor such as strain-rate sensitivity, optimum strain-rate and strength coefficient were obtained.

• 한국표면공학회지
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• 제29권6호
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• pp.857-861
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• 1996

The influence of rf-plasma operation on the thin film formation containing small particles for Al-Li alloys mainly have been studied as a function of Ar gas pressure and plasma power by means of a 200kV transmission electron microscope (TEM). Under the non-plasma operation, the transition from continuous thin films to clusters of grape-like small particles occurred at Ar gas pressures above 20Pa. Particles were single crystals with clear crystal habit planes. Under the plasma operation, the influence of gas pressures on the film formation at a plasma power of 5W was also examined. Thin films containing particles below 30Pa and the films containing mainly particles above 40Pa were formed. The prominent change of the average particle size was not recognized. The increase of the plasma powers at 20Pa, which formed particles under non-plasma, suppressed growth of particles, and homogeneous films containing very small particles were fabricated. The electric conductivity showed slight decrease with an increase of plasma power.