Seung-Eon Kim

Phase transformation and microstructure of NiAl/Ni3Al alloys containing Ti

Abstract The effects of titanium additions on A s temperature, phase transformation behavior and microstructure have been studied in β+γ ′ two-phase alloys. When the endothermic β ′ →β transformation appeared first during heating of martensite, a mesh type microstructure, which has no resemblance to the original martensite plates, was obtained.

Microstructure control in two-phase (B2+L12) Ni–Al–Fe alloys by addition of carbon

Abstract Carbon and titanium were added in two-phase (B2+L1 2 ) Ni–Al–Fe alloys for carbides precipitation, and the additions of 0.2 wt.% C and 3 at.% Ti have been found to produce the most adequate high temperature structural material. Carbon doped alloys showed more refined microstructure than carbon free alloys. The carbides, which were formed in the as-cast microstructure showing equiaxed dendrites, appeared to play a role in suppressing grain growth and coarsening of the second phases. The NAF29-10 alloy, including no carbides, showed the lamellar type microstructure, while the NAF29-10-C alloy, including carbides, showed a much more refined mesh type microstructure. When the carbon free alloys were quenched into water, cracks occurred at the grain boundaries probably due to martensitic transformation, however, these cracks were not observed in the carbon doped alloys. In order to suppress quenching cracks in the carbon free alloys, the solutionizing treatment time was reduced. However, cracks still formed as a severe intergranular mode at an early stage of elastic deformation. The refined microstructure of carbon doped alloys could compensate for elongation loss due to solution hardening and precipitation hardening. As a result, the carbon doped alloys showed good room temperature ductility and also showed much higher yield strength than other alloys including no carbides over the entire temperature range.

Characteristics of Porous Titanium Fabricated by Space-holder Method using NaCl

This study was performed to fabricate the porous titanium foam by space holder method using NaCl powder, and to evaluate the effect of NaCl volume fractions (33.3~66.6 vol.%) on the porosities, compressive strength, Young`s modulus and permeability. For controlling pore size, CP titanium and NaCl particles were sieved to different size range of 70~150 and 300~425 respectively. NaCl of green Ti compact was removed in water followed by sintered at for 2 hours. Total porosities of titanium foam were in the range of 38-70%. Pore shape was a regular hexahedron similar that of NaCl shape. Porous Ti body showed that Young`s modulus and compressive strength were in the range of 0.6-6 GPa and 8-127 MPa respectively. It showed that pore size and mechanical properties of Ti foams was controllable by NaCl size and volume fractions.

Fabrication of Porous 3-Dimensional Ti Scaffold and Its Bioactivity by Alkali Treatment

)Abstract Ti scaffolds with a three-dimensional porous structure were successfully fabricated using powdermetallurgy and modified rapid prototyping (RP) process. The fabricated Ti scaffolds showed a highly porousstructure with interconnected pores. The porosity and pore size of the scaffolds were in the range of 66~72%and 300~400µm, respectively. The sintering of the fabricated scaffolds under the vacuum caused the Tiparticles to bond to each other. The strength of the scaffolds depended on the layering patterns. Thecompressive strength of the scaffolds ranged from 15 MPa to 52 MPa according to the scaffolds’ architecture.The alkali treatment of the fabricated scaffolds in an aqueous NaOH solution was shown to be effective inimproving the bioactivity. The surface of the alkali-treated Ti scaffolds had a nano-sized fibre-like structure.The modified surface showed a good apatite forming ability. The apatite was formed on the surface of the alkalitreated Ti scaffolds within 1 day. The thickness of the apatite increased when the soaking time in a simulatedbody fluid (SBF) solution increased. It is expected that the surface modification of Ti scaffolds by alkalitreatment could be effective in forming apatites in vivo and can subsequently enhance bone formation.Key wordsTi scaffold, alkali treatment, SBF, bioactivity, rapid prototyping.

RF 스퍼터링으로 증착된 하이드록시아파타이트 박막의 열처리 특성

【RF sputtering process was applied to produce thin hydroxyapatite(HAp) films on Ti-6Al-4V alloy substrates. The effects of different heat treatment conditions on the hardness between HAp thin films and Ti-6Al-4V alloy substrates were studied. Before deposition, the Ti-6Al-4V alloy substrates were heat treated for 1h at

The ESCA Analysis of Hydroxyapatite Thin Films Deposited by RF Sputtering

850^{\circ}C\;under\;3.0{\times}10^{-3}torr

Bioactive glass–poly (ε-caprolactone) composite scaffolds with 3 dimensionally hierarchical pore networks

, and after deposition, the HAp thin films were heat treated for 1h at

Porous material having hierarchical porous structure and preparation method thereof

400^{\circ}C,\;600^{\circ}C\;and\;800^{\circ}C

Preparation of bioactive glass ceramic beads with hierarchical pore structure using polymer self-assembly technique

under the atmosphere, and analyzed FESEM-EDX, FTIR, XRD, nano-indentor, micro-vickers hardness, respectively. Experimental results represented that the surface defects of thin films decreased by relaxation of internal stress and control of substrate structure followed by heat treatment of substrates before the deposition, and the HAp thin films on the heat-treated substrates had higher hardness than none heattreated substrates before the deposition, and the hardness properties of HAp thin films and Ti-6Al-4V alloy substrates appeared independent behavior, and the hardness of HAp thin films decreased by formation of

Deposition of NiAl coating for improvement of oxidation resistance of cold-rolled Ni3Al foils

VTiO_3(OH),\;{\theta}-Al_{0.32}V_2O_5,\;Al_{0.33}V_2O_5