• Journal of Powder Materials
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• v.20 no.5
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• pp.323-331
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• 2013

In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 ${\mu}m$ FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.6
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• pp.279-284
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• 2017

Mechanical properties of titanium alloy can be improved by controlling microstructure through heat treatment. In this study, Ti-3Al-8V-6Cr-4Mo-4Zr metastable beta titanium alloy, was controlled for excellent mechanical property and sound formability through various high temperature heat treatment and aging conditions and the optimum heat treatment conditions were determined. The specimens were heat-treated at $950^{\circ}C$, followed by various aging treatments from $430^{\circ}C$ to $500^{\circ}C$ for 1 to 24 h. As aging temperature and holding time increased, hardness increased by ${\beta}^{\prime}$ phase formation and precipitation of secondary ${\alpha}$ phase in ${\beta}$ matrix. However, the optimum aging temperature and holding time for mechanical properties were at $450{\sim}470^{\circ}C$ for 8~16 hr. Hardness values of the specimen aged at $450^{\circ}C$ for 8 h were found to be the highest. These results can be effectively applied to fabrication of spring with better formability and mechanical property.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.1
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• pp.1-8
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• 1994

Lattice structure, hydrogen absorption characteristics, discharge capacity and cycle life of $V_{22}Ti_{16}Zr_{16}Ni_{39}X_7$(X= Cr, Co, Fe, Mn, Al) alloys were investigated. The matrix phases of these alloys were the C14 Laves phase. Chromium-containing alloy had a vanadium-rich phase in addition to the Laves phase. The chromium, maganese, or aluminum-containing alloys had lower hydrogen equilibrium pressure and larger hydrogen absorption content than the cobalt or iron-containing alloys. The discharge capacities of these alloys were 270~330mAh/g. The discharge capacity according to the alloying element X decreased in the order of Mn>Cr>Co, Al)Fe. The charge/discharge cycle lives of the chromium, cobalt or iron-containing alloys were longer than those of maganese or aluminum-containing alloys due to the lower vanadium dissolution rate.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.5
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• pp.459-464
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• 2017

The volume expansions of $Ti_{0.95}Zr_{0.05}V_{0.4}Mn_{1.45}Fe_{0.1}Cr_{0.05}$ alloy during hydrogenation with various conditions have been investigated. The theoretical volume expansion measured with XRD for this alloy with hydrogenation was 21%. The apparent volume expansion of this alloy ingot with hydrogenation was composed of two effects. One is a hydrogenation and the other is a pulverization. The apparent volume of free alloy powder was 1.8 times greater than that of an ingot, implying the pulverization effect on the apparent volume expansion is 80%. The apparent volume expansion of the alloy ingot with hydrogenation under a unconstrained condition was about 80 (${\pm}15$)%, much smaller than that of free alloy powder which expected as 118%. In addition, The apparent volume expansion of the alloy ingot with hydrogenation under a constrained condition(Al container) was about 50%, much smaller than that of the unconsrained. This reduced apparent volume expansion of the alloy ingot could be attributed to an arrangement of alloy powder keeping its original shape of the ingot even after hydrogenation.

• Korean Journal of Materials Research
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• v.14 no.1
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• pp.13-18
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• 2004

Titanium alloys are the one of promising candidate materials for medium high temperature parts in the aircraft, automobile, petrochemistry and electrochemistry because of their high strength with low density in medium high temperature. In this study, the effects of aging and heat treatments on the mechanical properties of Ti-15-3 alloy in medium high temperature, which was $400^{\circ}C$, were studied. Solid solution treatment was performed at $8000^{\circ}C$ of $\beta$ phase region for 1 h and the alloy was quenched in water. The alloy was aged at $5000^{\circ}C$ of $\alpha$ and $\beta$ two-phase region for 1, 2, 4, 8, ... and 100 h to increase the mechanical property. The $\beta$ single phase was observed at all parts of specimens in Ti-15-3 alloy after ST. As the aging at $500^{\circ}C$, fine precipitates of a phase was generated from matrix of $\beta$ phase and the microstructure was consisted of weaving structure such as Widmanstiitten a phase. The most suitable aging time is 24h in$ 400^{\circ}C$. At this time, strength is 1164 MPa and elongation is about 12%. In room temperature, elongation of Ti-15-3 alloy aged at $500^{\circ}C$ for 16 h is poor (=3%) in spite of high tensile strength (1458 MPa).

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.640-644
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• 2003

NiCr thin films were fabricated by rf magnetron sputtering for applying to both the top electrode and absorption layer on Pb(Zr, Ti)O$_3$(PZT) thin films for infrared sensors. The rms roughness and resistivity of NiCr films prepared with Ni power of 80 W and Cr power of 50 W showed the most stable oxidation resistance after annealing at $600^{\circ}C$ for 5 min in oxygen ambient. The rms roughness and resistivity of NiCr films annealed at $V^{\circ}C$ in oxygen ambient were about 2$0\AA$ and $70 \mu$Ω-cm, respectively. As-deposited Ni/PZT/Pt and NiCr (Ni 80 W, Cr 50 W)/PZT/Pt structures showed well saturated hysteresis loops. However, in case of the samples annealed at $500^{\circ}C$ in oxygen ambient, only NiCr/PZT/Pt showed saturated loops having a remanent polarization of 20$\mu$C/$\textrm{cm}^2$. Ultra-thin NiCr films showed a possibility as a top electrode for infrared sensors.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.619-624
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• 2009

Titanium alloys have been attractive due to a high ratio of strength to weight as well as good corrosion resistance. However, strengthening causes a decrease in ductility in Ti alloys, as is usual in other alloys. For enhanced strength without ductility reduction, grain refinement and tensile properties were investigated as functions of thickness reduction of cold rolling and annealing condition in Ti-15V-3Cr-3Sn-3Al alloy with a ${\beta}$ single phase. The average grain size of the specimen, which was cold-rolled by 90% and annealed at 700$^{\circ}C$ for 5 min, was decreased to approximately 19 ${\mu}m$. The grain refinement of 63 μm to 19 ${\mu}m$ increased yield stress by 90 MPa without a significant decrease in total elongation. The Ti-15-3 alloy exhibited very low work hardening during tensile test at a crosshead speed of 2 mm/min. This result was discussed based on dynamic recovery associated with dislocation annihilation in grain boundaries.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.45-51
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• 1998

[ $AB_2-type$ ] alloy, one kind of hydrogen storage alloys used as an anode of Ni-MH batteries, has large discharge capacity but has remaining problems regarding initial activation, cycle life and self-discharge. This study investigates the effects of Cr-addition and fluorination after La-addition on $Zr_{0.7}Ti_{0.3}V_{0.4}Mn_{0.4}Ni_{1.2}$, composition $AB_2-type$ alloy. EPMA and SEM surface analysis techniques were used and the crystal structure was characterized by XRD analysis. In addition, electrodes were fabricated out of the alloys and characterized by constant current cycling test, electrochemical impedance spectroscopy and potentiodynamic polarization. Cr-addition was found to be effective to cycle life and self-discharge but ineffective to initial activation due to formation of stable oxide film on surface. Fluorination after La-addition to the alloys improved initial activation remarkably due to formation of highly reactive particles on surface.

• Journal of Technologic Dentistry
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• v.25 no.1
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• pp.89-94
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• 2003

The use of titanium alloys as biomaterials is increasing due to their superior biocompatibility and enhanced corrosion resistance compared to conventional stainless steels and cobalt-based alloys. Ti-6Al-4V ($\alpha+\beta$type) alloy instead of pure titanium ($\alpha$type) is being widely used as biomaterials has some characteristics such as high fatigue strength, tensile strength and corrosion resistance. It also has similar characteristics to Ti in inducing bony ingrowth. But it has been reported recently that the vanadium element expresses cytotoxicity and carcinogenicity and the aluminium element is related with dementia of Alzheimer type and neurotoxicity. In order to overcome their detrimental effects, $\beta$-phase stabilizer Nb was chosen in the present study. CP-Ti(ASTM grade 2), Ti-3wt.%Nb($\alpha$type), Ti-20wt.%Nb ($\alpha+\beta$type) and Ti-40 wt.%Nb($\beta$type) alloys were melted by vacuum arc furnace. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows: 1. For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to CP-Ti(ASTM grade 2), 316L STS and Co-Cr alloys.

• Transactions on Electrical and Electronic Materials
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• v.4 no.1
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• pp.15-20
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• 2003

NiCr alloys are prepared onto poly-Si/ $SiO_2$/Si substrates to replace Pt bottom electrode with a new one for integration of high dielectric constant materials. Alloys deposited at Ni and Cr power of 40 and 40 W showed optimum properties in the composition of N $i_{1.6}$C $r_{1.0}$. The grain size of films increases with increasing deposition temperature. The films deposited at 50$0^{\circ}C$ showed a severe agglomeration due to homogeneous nucleation. The NiCr alloys from the rms roughness and resistivity data showed a thermal stability independent of increasing annealing temperature. The 80 nm thick BST films deposited onto N $i_{1.6}$C $r_{1.0}$/poly-Si showed a dielectric constant of 280 and a dissipation factor of about 5 % at 100 kHz. The leakage current density of as-deposited BST films was about 5$\times$10$^{-7}$ A/$\textrm{cm}^2$ at an applied voltage of 1 V. The NiCr alloys are possible to replace Pt bottom electrode with new one to integrate f3r high dielectric constant materials.terials.