• Journal of the Korean Society for Heat Treatment
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• v.9 no.2
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• pp.121-129
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• 1996

The solubility of Ti in Al matrix was determined by X-ray diffraction method on two different mechanical alloying systems, i.e Al+$Al_3Ti$ and Al+Ti alloys. Starting powder compositions of two systems were chosen for final volume fraction of $Al_3Ti$ phase being 25%. The solubility of Ti in ${\alpha}$-Al was estimated by the lattice parameter measurement of Al. For Al+$Al_3Ti$ mixture, it appeared that some of $Al_3Ti$ particles decomposed during milling and maximum solubility of Ti in Al was about 0.99%. The majority of $Al_3Ti$ particles were dispersed uniformly in Al matrix, having approximate size of 100~200 nm. On the other hand, higher Ti solubility of 1.24 wt.% was found in Al+Ti system, with starting composition of Al+10 wt.%Ti. After 15 hours of milling, Ti phase was identified as 20 nm sized particles embedded in Al matrix. The annealing of mechanically alloyed powders from Al+$Al_3Ti$ and Al+10 wt.%Ti systems was followed in the temperature range of 200 to $600^{\circ}C$ to study thermal stability of supersaturated solution of Al(Ti). After annealing, the lattice parameter of Al reverted back to that of pure Al, and the peak intensity ratio of $Al_3Ti$/Al was increased more than the original value before annealing. These results suggest that Ti dissolve into alpha-Al solutions during milling, and by annealing, $Do_{22}-Al_3Ti$ phase forms from Al(Ti) solution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.107-110
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• 1999

The ultrasonic spray method was employed to make (Y,Gd)BO$_3$:Eu Phosphor, and its optical properties under 147nm VUV and 254 nm UV excitations were characterized and then compared with that produced by the solid-state reaction. The mixed solution of acetate hydrates of Y, Gd, Eu and boric acid diluted in water or methanol was used as the precursor fur the spray. It was found that (Y,Gd)BO$_3$:Eu phosphor made by this ultrasonic spray had a spherical shape and fine particle size of 1${\mu}{\textrm}{m}$. The crystalline structure for the as-sprayed phosphor was amorphous, but it converted into the same polycrystalline phase of solid state reaction after post heat treatment at 110$0^{\circ}C$ for 2hr. The emitting intensity under VUV and UV excitations for the spray-formed (Y,Gd)BO$_3$:Eu phosphor, however, was inferior to the later one. The excitation spectra were also studied and compared under VUV and UV excitations to explain the change of emitting intensity with Gd substitution in (Y$_{1-x}$ Gd$_{x}$)BO$_3$:Eu Phosphors made by spray and solid state reaction.on.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.1
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• pp.1-6
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• 2015

The ductile-to-brittle transition behavior of two austenitic Fe-18Cr-10Mn alloys with the combined addition of nitrogen and carbon was investigated in this study. The alloys exhibited a ductile-to-brittle transition behavior because of unusual brittle fracture at low temperatures unlike conventional austenitic alloys. The alloy with higher carbon content had higher yield and tensile strengths than that with lower carbon content due to the solid solution strengthening effect resulting from carbon addition. However, the increase in carbon content promoted the occurrence of intergranular fracture, and thus deteriorated the impact toughness. In order to develop successfully the austenitic Fe-18Cr-10Mn alloys with the excellent combination of strength and toughness in the future, therefore, more systematic studies are required to find the appropriate amount and ratio of nitrogen and carbon.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.5
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• pp.251-258
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• 2008

A transmission electron microscope investigation has been performed on the morphology of dislocations in deformed ${\gamma}^{\prime}-Ni_3(Al,Ti)$ alloys containing fine dispersion of disordered ${\gamma}$ particles. Superlattice dislocations dissociate into fourfold Shockley partial dislocations in a uniform supersaturated solid solution of the ${\gamma}^{\prime}$ phase. Dislocations are attracted into the disordered ${\gamma}$ phase and dissociate further in the particles. At any stage of aging, dislocations cut through the particles and the Orowan bypassing process does not occur even in the over-aged stage of this alloy system. The work necessary to pull the dislocation away from the disordered particles into the ordered matrix should mainly contribute to increase the strength of the ${\gamma}^{\prime}$ phase containing fine dispersion of the disordered ${\gamma}$ phase.

• Korean Journal of Materials Research
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• v.26 no.5
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• pp.235-240
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• 2016

Appropriate thermo-mechanical properties of nickel-based superalloys are achieved by heat treatment, which induces precipitation and solid solution hardening; thus, information on the temperature ranges of precipitation and dissolution of the precipitates is essential for the determination of the heat treatment condition. In this study, thermal analyses of nickel-based superalloys were performed by differential scanning calorimetry method under conditions of various heating rates of 5, 10, 20, or 40K/min in a temperature range of 298~1573K. Precipitation and dissolution temperatures were determined by measuring peak temperatures, constructing trend lines, and extrapolating those lines to the zero heating rate to find the exact temperature under isothermal condition. Determined temperatures for the precipitation reactions were 813, 952, and 1062K. Determined onset, peak, and offset temperatures of the first dissolution reaction were 1302, 1388, and 1406K, respectively, and those values of the second dissolution reaction were 1405, 1414, and 1462K. Determined solvus temperature was 1462K. The study showed that it was possible to use a simple method to obtain accurate phase transition temperatures under isothermal condition.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.5
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• pp.346-354
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• 2000

Effect of Nb addition on the phase transformation behavior was studied through continuous cooling transformation tests after reheating(reheating CCT) and deforming(deforming CCT) the 0.07%C-1.3%Mn-0.015%Ti-(0~0.08)% Nb steels. Transformation temperatures for deforming CCT were lower than those for reheating CCT, and the critical cooling rate for bainite transformation during deforming CCT was lower than that during reheating CCT. These enhanced hardenability for deforming CCT was considered to come from the sufficient solid solution of Nb in austenite during high temperature reheating before deformation. With Nb addition, the phase transformation temperature decreased, the bainite formation was enhanced, and the hardness of steel increased. Furthermore, these phenomena were more remarkable for deforming CCT than for reheating CCT. From the results, Nb-Ti bearing low carbon steel was considered to be a very favorable alloy system with good strength/toughness balance by recrystallization control rolling process.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.168-176
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• 1998

The mechanical properties of mechanically alloyed Al-4wt%Mg alloys dispersed with $MgAl_2O_4$ dispersoilds at room and elevated temperatures were investigated. The powders in steady state during mechanical alloying consisted of Mg-supersatu rated Al solid solution and $Al_4C_3$ which resulted from the reaction of Al with C in process control agent (methanol). The hot-extruded materials consisted of uniformly dispersed fine $MgAl_2O_4$, ${\gamma}-Al_2O_3$, $Al_2O_3$ and matrix with extremly fine substructure. Tensile specimens prepared from the extruded bars were tested at room temperature to $400^{\circ}C$ under different strain rates. The tensile strength of alloys at room temperature ranged from 500 to 594MPa. At elevated temperatures, the tensile strengths and elongations decreased with increasing temperature. Adding 3% $MgAl_2O_4$ to Al-4wt%Mg increased the tensile strength of 50MPa at rowan temperature and 20MPa at $400^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.3
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• pp.145-152
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• 2023

β titanium alloys containing β stabilizing elements such as V, Nb, Ta, Mo and Fe are widely used etc, due to their excellent specific strength, corrosion resistance, fatigue strength and easy formability. New metastable β titanium alloys are developed containing low-cost elements (Mo and Fe) in this study. Fe element is a strong β-stabilizer which can affect the mechanical and electrochemical properties of Ti-5Mo-xFe (x = 1, 4 wt%) alloys. These properties were analyzed in connection with microstructure and phase distribution. Ti-5Mo-4Fe alloy showed higher compression yield stress and maximum stress than Ti-5Mo-1Fe alloy due to solid-solution hardening and grain refinement hardening effect. As Fe element increased, Fe oxide formation and reduction of ${\bar{Bo}}$ (bond order) value affect the decrease of corrosion resistance. Ti-5Mo-xFe alloys were more excellent than Ti-6Al-4V ELI alloy.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.525-531
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• 2007

The operating temperature has been increased to improve the efficiency of gas turbine. The most advanced Gas turbine is operated at above $1,500^{\circ}C$. Improvement in material and cooling method permit hot gas path component to run at increased temperature. But, the repair of blades which are developed with advanced manufacture technique is difficult to use normal welding. Most of gas turbine blades are made of precipitation harden nickel base superalloy, which is very hard to weld. Therefore, the employment of welding filler on blade is solid solution nickel base superalloy(Hastelloy X, Inconel 617). In this study, Tensile test in high temperature was conducted on welded GTD111DS with GTD111 to evaluate effect of variation of pre, post treatment. The result of this study showed that the specimen was treated with optimum pre and post treatment(preweld HT($1200^{\circ}C$), Post treatment($1100^{\circ}C$ HIP, $1200^{\circ}C$ + $1100^{\circ}C$ + $800^{\circ}C$ HT) is mush superior.