• Korean Journal of Materials Research
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• v.18 no.1
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• pp.51-56
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• 2008

The crystal structures and morphologies of precipitates in $L1_0$-ordered TiAl intermetallics containing nitrogen were investigated by transmission electron microscopy (TEM). Under aging at an approximate temperature of 1073 K after quenching from 1423 K, TiAl hardens appreciably due to the nitride precipitation. TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$-TiAl matrix, appear in the matrix preferentially at the dislocations. Selected area electron diffraction (SAED) pattern analyses showed that the needle-shaped precipitate is perovskite-type $Ti_3AlN$ (P-phase). The orientation relationship between the P-phase and the $L1_0$-TiAl matrix was found to be $(001)_P//(001)_{TiAl}\;and\;[010]_P//[010]_{TiAl}$. By aging at higher temperatures or for longer periods at 1073 K, plate-like precipitates of $Ti_2AlN$ (H-phase) with a hexagonal structure formed on the {111} planes of the $L1_0$-TiAl matrix. The orientation relationship between the $Ti_2AlN$ and the $L1_0$-TiAl matrix is $(0001)_H//(111)_{TiAl}\;and\;_H//_{TiAl}$.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.394-399
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• 2000

The effects of the type and thickness of underlayer on the crystallographic texture and the sheet resistance of aluminum thin film were studied. Ti and Ti/TiN were examined as the underlayer of aluminum. Ti and TiN were prepared by ionized physical vapor deposition (I-PVD) metalorganic chemical vapor deposition (MOCVD), respectively. The texture and the sheet resistance of metal thin film stacks were investigated at various thicknesses of Ti or TiN, and the sheet resistance was measured after annealing at $400^{\circ}C$ in an nitrogen ambient. For I-PVD Ti underlayer, the excellent texture of aluminum <111> was obtained even at top of 5 nm of Ti. However, the sheet resistance of the metal stack was greatly increased after annealing due to the interdiffusion and reaction of Al and Ti. MOCVD TiN between Ti and Al could suppress the Al-Ti reaction without severe degradation of aluminum <111> texture. Excellent texture of aluminum was obtained for the MOCVD TiN thinner than 4 nm.

• Journal of the Korean institute of surface engineering
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• v.31 no.3
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• pp.157-164
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• 1998

Effects of alloying elements on the pitting behavior of Ti-Al intermetalic compounds in the electrolytic soution containing Cl- were investigated through electrochemical tets and corrosion morphologies. Corrosion potential increased in the case of Cr addition to Ti-48%Al, whereas it decreased in the case of Si and B addition. The simultaneous addition of Cr and Si increased passive current density and decrosion corrosion potential. The passive current density of N addtion was higher than that of B addition in H2SO4 solution. With the addition of alloying elements, The pitting resistance decreased in order of TiAl>TiAlSi>TiAlN>TiAlB>TiAlCr and whin siumultaneous addition, it decreased in order of TiAlCrSi>TiAlCrBN>TiAlCrrN. The surface merohology after pitting test showed that the TiAl coataining Si had for fewer pits than that containing Cr and N simultaneously.

• Korean Journal of Materials Research
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• v.27 no.11
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• pp.603-608
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• 2017

$Si_3N_4$ is a ceramic material attracting attention in many fields because of its excellent abrasion resistance. In addition, Ti and TiAl alloys are metals used in a variety of high temperature environments, and have attracted much attention because of their high strength and high melting points. Therefore, study of the interface reaction between $Si_3N_4/Ti$ and $Si_3N_4/TiAl$ can be a useful practice to identify phase selection and diffusion control. In this study, $Si_3N_4/Ti_5Si_3+TiN/TiN/Ti$ diffusing pairs were formed in the $Si_3N_4/Ti$ interfacial reaction and $Si_3N_4/TiN(Al)/Ti_3Al/TiAl$ diffusion pathway was identified in the $Si_3N_4/TiAl$ interfacial reaction. The diffusion layers of the interface reactions were identified and, to investigate the kinetics of the diffusion layer, the integrated diffusion coefficients were estimated.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.124-133
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• 2003

Ti-25Al-xNb (x=0, 3, 7, 11, 13 at. %) alloys and 18 vol. % TiB/(Ti-25Al-11Nb) metal matrix composite were fabricated by spark plasma sintering process at 900-120$0^{\circ}C$. Microstructural characteristics of the sintered bodies were identified by SEM, EDX analysis, X-ray diffraction, and differential scanning calorimeterric method. $Ti_3Al$ alloy was consisted of equiaxed $\alpha_2$ phase. $Ti_3Al-Nb$ alloys and the matix of TiB/(Ti-25Al-11Nb) metal matrix composite had the morphology that O phase was precipitated at the grain boundary of $\alpha_2$phase. Volume fraction of O phase and hardness were depended on the concentration of Nb in $Ti_3Al-Nb$ alloy, Rule of mixing could be applied to hardness and Young's modulus of 18 vol. % TiB/(Ti-25Al-11Nb) metal matrix composite.

• Journal of Korea Foundry Society
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• v.30 no.4
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• pp.147-150
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• 2010

An eco-friendly production technique of Al-8.6Ti-0.025C refiner was developed by melting a Al-Ti master alloy in a graphite crucible, in which the potential nucleation site, TiC effectively formed by the spontaneous in-situ reaction between excessive Ti and carbon from graphite crucible. The A3003 alloy refined by the Al-8.6Ti-0.025C showed effectively refined macrostructure and enhanced mechanical properties comparable to the commercial Al-Ti-B refiner. The effective refinement was achieved in a shorter compare to the melt-treating time commercial Al-Ti-B refiner.

• Journal of Powder Materials
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• v.6 no.1
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• pp.42-48
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• 1999

Three mixtures of elemental powders of Al-25at.%Ti, 48at.%Ti and 70at.%Ti were offered to ball milling process for the formation of intermetallic compounds of $Al_3Ti$, AlTi and $Ti_3Al$. Ballmilling or attrition process were carried out at the condition of rotaing speed of 110 or 350 rpm at $10^{-3}$ torr vacuum or argon atmospheres. $Al_3Ti$phases were fully obtained by heat treatment for 1 hors at $600^{\circ}C$ with Al-25at.%Ti composition mixtures milled by 100 hours. The amorphous phase was completely formed at the composition of Al-48at.%Ti mixed powders by milling 100hours at the 50 to 1 weight ratio of ball to powder, and AlTi compounds were obtained by heat treament. In the case of Al-70at%Ti mixed powders milled for 100 hours, $Ti_3Al$ and $Al_3Ti$intermetallic compounds were formed by heat treatment for 1 hour at $600^{\circ}C$. By attrition milling of 350rpm for 10 hours, $Ti_3Al$ phase was formed completley after heat treatment for 1 hour at $600^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.25 no.5
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• pp.235-252
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• 1992

(Ti, Al)N films were deposited on 304 stainless steel sheet by D.C. magnetron sputtering using Al target and Ti plate. The high temperature oxidation of (T, Al)N films with the variation of composition has been investigated. The chemical composition of (Ti, Al)N films with the variation of composition has been investigated. The chemical composition of (Ti, Al)N films was similar to the sputter area ratio of titanium to aluminum target by means of EDS and AES survey. The high temperature oxidation test of (Ti, Al)N showed that (Ti, Al)N has better high temperature resistance than TiN and TiC films. TiC films were cracked at 40$0^{\circ}C$ in air TiN films quickly were oxidised at $600^{\circ}C$, were spalled more than $700^{\circ}C$. But (Ti, Al)N films are relatively stable to$ 900^{\circ}C$. The good resistance to high temperature oxida-tion of (Ti, Al)N films are due to the formation of dense Al2O3 and TiO2 oxide layer. Especially, Al2O3 oxide layer is more important. The results obtained from this study show, it is believe that the (Ti, Al)N film by D.C. magnetron sputtering is promising for the use of high temperature and wear resistance mate-rials.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.7
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• pp.711-717
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• 2013

Titanium (Ti) metal and its alloys are desirable materials for ship hulls and other structures because of their high strength, light weight and corrosion-resistance. And light weight and corrosion-resistant aluminum (Al) is the ideal metal for shipbuilding. The joining of Ti and Al dissimilar metals is one of the effective measures to reduce weight of the structures or to save rare metals. Ti and Al have great differences in materials properties, and intermetallic compounds such as Ti3Al, TiAl, TiAl3 are easily formed at the contacting surface between Ti and Al. Thus, welding or joining of Ti and Al is considered to be extremely difficult. However, it was clarified that ultra-high speed welding could suppress the formation of intermetallic compounds in the previous study. Results of tensile shear strength increases with an increase in the welding speed, and therefore extremely high welding speed (50m/min in this study) is good to dissimilar weldability for Ti and Al. In this study, therefore, full penetration dissimilar lap welding of Ti (upper) - Al (lower) and Al (upper) - Ti (lower) with single-mode fiber laser was tried at ultra-high welding speed, and the microstructure of the interface zones in the dissimilar Al and Ti weld beads was investigated.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.133-139
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• 2014

Titanium (Ti) metal and its alloys are desirable materials for ship hulls and other ocean structures because of their high strength, corrosion-resistance and light weight properties. And light weight and corrosion-resistant aluminum (Al) is the ideal metal for shipbuilding. The joining of Ti and Al dissimilar metals is one of the effective methode to reduce weight of the structures. Ti and Al have great differences in materials properties, and intermetallic compounds such as $Ti_3Al$, TiAl, $TiAl_3$ are easily formed at the contacting surface between Ti and Al. Thus, dissimilar welding and joining of Ti and Al are considered to be very difficult. However, it was clarified that ultra-high speed welding could suppress the formation of intermetallic compounds in the previous study. Results of tensile shear strength increases with an increase in the welding speed, and therefore extremely high welding speed (50 m/min) is good to dissimilar weldability for Ti and Al. In this study, therefore, full penetration dissimilar lap welding of Ti (upper) - Al (lower) and Al (upper) - Ti (lower) with single-mode fiber laser was tried at ultra-high welding speed, and the microstructure of the interface zones in the dissimilar Al and Ti weld beads was investigated.