• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.65-71
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• 2005

Experimental Ti-13%Zr and Ti-13%Zr-5%Cu alloys were made in an argon-arc melting furnace. The grade 2 CP Ti was used to control. The alloys were cast into phosphate bonded $SiO_2$ investment molds using an argon-arc casting machine, and The hardness and microstructures of the castings were investigated in order to reveal their possible use for new dental casting materials and to collect useful data for alloy design. The hardness of the Ti-13%Zr-5%Cu alloy(379Hv) became higher than that of Ti-13%Zr(317Hv) alloy, and the hardness of this alloys became higher than that of CP Ti(247Hv). Increasing in the hardness of the Ti-13%Zr-5%Cu alloy was considered to be solid solution hardening as the Ti-Zr system shows a completely solid solution for both high temperature $\beta$phase and low temperature $\alpha$ phase and also the inclusion of the eutectoid structure($\alpha Ti+Ti_{2}Cu$). No martensitic structures are observed in the specimen made of CP Ti, but Ti-13%Zr and Ti-13%Zr-5%Cu alloys show a kind of martensitic structure. Ti-13%Zr-5%Cu shows the finest microstructure. From these results, it was concluded that new alloys for dental casting materials should be designed as Ti-Zr-Cu based alloys.

• Journal of Industrial Technology
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• v.19
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• pp.75-79
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• 1999

Rotary bending fatigue tests were performed to investigate the effects of 2-phase matrix structure on fatigue limit with prepared specimens in high strength ductile irons. Two types of the specimens with different microstructures have been used. Series A has sorbite and series B has bainite. Fatigue limits of both specimens are improved comparing with as cast specimen. The fatigue limit is higher in series B than in series A. The reason why the fatigue limit of series A shows inferiority to that of series B is due to the transition of micro fatigue cracks to mesocrack occurs very rapidly, so increased stress intensity factor drives the fatigue crack growth. The higher fatigue limit of series B which has bainite is caused by the ${\gamma}$ layer contained in microstructure impede the rapid growth of micro fatigue crack to mesocrack and ${\alpha}$ layer around graphite has the higher capacity for the absorption of plastic deformation energy than sorbite.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.357-363
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• 1998

Microstructure of A356 aluminium alloys cast in a permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. It was concluded that Fe impurity element to be crystallized into needlelike intermetallics was tied up by Be addition element, and new phases were crystallized into script or Be-rich intermetallics.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.544-551
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• 2017

In order to develop a new commercial Al-12%Si casting alloy with improved physical properties, we investigated the effect of adding Sr and TiB to the alloy. Al-12%Si alloys were prepared by die casting at $660^{\circ}C$. The eutectic temperature of the Sr-modified Al-12%Si alloy decreased to $9^{\circ}C$ and the mushy zone region increased. The shape of the Si phase changed from coarse acicula to fine fiber with the addition of Sr. The addition of TiB in the Al-12%Si alloy reduced the size of the primary ${\alpha}$-Al and eutectic Si phases. When Sr and TiB were added together, it worked more effectively in refinement and modification. The density of twins in the Si phase-doped Sr increased and the width of the twins was refined to 5 nm. These results are related to the impurity induced twinning(IIT) growth.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.4
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• pp.190-199
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• 2015

The study is intended to investigate the effect of solution treatment on microstructure and corrosion behavior of AZ91(Mg-9%Al-1%Zn-0.3%Mn)-2%Ca casting alloy. In as-cast state, the AZ91-2%Ca alloy consisted of intermetallic ${\beta}(Mg_{17}Al_{12})$, $Al_8Mn_5$ and $Al_2Ca$ phases in ${\alpha}-(Mg)$ matrix. After the solution treatment, Al within the ${\alpha}-(Mg)$ matrix was distributed more homogeneously, along with the slight decrease in the total amount of intermetallic compounds. The corrosion resistance of the AZ91-2%Ca alloy was improved after the solution treatment. The microstructural examinations for the solution-treated samples revealed that the better corrosion resistance may well be related to the incorporation of more oxides and hydroxides such as $Al_2O_3$, $Al(OH)_3$, CaO and $Ca(OH)_2$ into the surface corrosion product without dissolution of the intermetallic phases along the grain boundaries.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.4
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• pp.180-184
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• 2014

In order to make clear relationship between high temperature tensile properties and fine microstructure of rapidly solidified cast-type Ni-base superalloys without heat treatment required for consolidation process, tensile test was carried out by changing strain rate from $5{\times}10^{-5}s^{-1}$ to $2{\times}10^{-2}s^{-1}$ and test temperature from $900^{\circ}C$ to $1050^{\circ}C$ using IN738LC and Rene'80 melt-spinning ribbons by twin roll process which were superior to ribbons by single roll process from the viewpoint of structure homogeneity. The dependence of tensile strength on strain rate and test temperature was studied and strain rate sensitivity, m, were estimated from tensile test results. From this study, it was found that tensile strength was influenced by ${\gamma}^{\prime}$ particle diameter, test temperature and strain rate, and m of ribbons exhibited above 0.3 over $950^{\circ}C$.

• Korean Journal of Materials Research
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• v.14 no.6
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• pp.379-388
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• 2004

To investigate the effect of D-ferrite on the hot workability and surface defect of STS 304 billets containing 3 wt. % Cu, microstructure observations and high temperature mechanical properties test were carried out for the specimens extracted mainly from raw or oxidized billets. It was found that the total $\delta$-ferrite content has little influence on the hot workability, even though the fracture cracks due to high temperature tension or compression test were initiated and propagated mostly along $\delta$/${\gamma}$ boundary in the specimens. On the other hand, it was supposed that the direct causes of surface defects in the wire rolled from the as-continuously cast billet were the grain boundary embrittlement arose from the deep diffusion of oxygen into the grain boundary, and the oxidation of $\delta$-ferrite connected by a grain boundary to the surface during the billet reheating process as well.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.1
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• pp.10-16
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• 2004

The aim of this study is to investigate the process conditions on the microstructual changes and mechanical properties of large 7175 aluminum ring roll forgings. The billets range from 370 mm to 720 mm in diameter were homogenized and ring roll forged after direct chill casting. The tensile properties of ring roll forged specimen manufactured with ${\Phi}370mm$ billets were superior to those of ${\Phi}720mm$ billets under $T_6$ condition. Also, these properties showed better than those of military specification under $T_{74}$ treatment. The impact value of ring roll forged specimen under $T_{74}$ treatment increased up to 20% than that of $T_6$ condition. The fracture toughness of ring roll forged specimen manufactured with ${\Phi}370mm$ cast billet showed nearly same level of ${\Phi}720mm$ billet which was processed using MF or Cog free forging followed by ring roll forging.

• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.24-32
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• 1999

A series of investigations for Austempered Ductile Iron (ADI) castings were carried out by using the specimens with various chemical compositions and heat treatment conditions. The rolling wear characteristics of alloyed austempered ductile irons under an unlubricated dry rolling condition was evaluated by the Amsler type test with 9.09% sliding ratio. Generally, the wear amount was increased with the austempering temperature and decreased when the hardness of the matrix was higher. The alloying elements also influenced the austempering reaction, the microstructure and the mechanical properties. In this study, the mechanical properties (i.e.) ultimate tensile strength (UTS), hardness, elongation) and the wear resistance are analysed to show the relationship between the alloying elements and the austempering temperatures. Mo, Cu and Ni are alloyed individually or in combination. It has been found that when Cu and Ni alloyed individually to a casting, the wear amount is increased than others with elements alloyed in combination. The amount of rolling wear loss was decreased when Mo was alloyed in cast iron, individually or in combination.

• Journal of Korea Foundry Society
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• v.17 no.3
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• pp.267-275
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• 1997

Fabrication of high strength Mg-Li-Al alloys by squeeze casting was established by the stabilization of melt and mold temperatures, applied pressure and the refining method. The entrapment of inclusions during pouring was prevented using 30 ppi alumina foam filter. The as-cast microstructure consists of a mixture of ${\alpha}$ and ${\beta}$ phases including AILi and $MgLi_2$, Al particles, which are distributed in the ${\beta}$ matrix. The grain sizes of gravity and squeeze casting alloys were 288 ${\mu}m$ and 207 ${\mu}m$ respectively. The addition of Al in Mg-Li alloys promoted the formation of second phase particles, which were adjusted to optimize the properties of Mg-Li-Al alloys. The Mg-10wt%Li-5wt%Al alloy after heat treatment at $350^{\circ}C$ for 1 hour showed the maximum hardness value. This is due to the facts that the amounts of ${\alpha}$ and ${\beta}$ phases and their distributions are dependent upon the solution treatment temperature, and that the amounts of AILi and $MgLi_2Al$ particles are dependent upon the Al content.