• The Journal of Advanced Prosthodontics
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• v.14 no.5
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• pp.285-293
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• 2022

PURPOSE. This study evaluated the relationship among translucency, crystalline phase, grain size, and fracture toughness of zirconia. MATERIALS AND METHODS. Four commercial zirconia - Prettau^®Anterior^® (PA), Prettau^® (P), InCorisZI (ZI), and InCorisTZI (TZI)- were selected for this study. The bar specimens were prepared to determine fracture toughness by using chevron notched beam method with four-point bending test. The grain size was evaluated by a mean linear intercept method using a scanning electron microscope. X-ray diffraction and Rietveld refinement were performed to evaluate the amount of tetragonal and cubic phases of zirconia. Contrast ratio (CR) was measured to investigate the level of translucency. RESULTS. PA had the lowest fracture toughness among other groups (P < .05). In addition, the mean fracture toughness of P was significantly less than that of ZI, but there was no difference compared with TZI. Regarding grain size measurement, PA had the largest average grain size among the groups. P obtained larger grain size than ZI and TZI (P < .05). However, there was no significant difference between ZI and TZI. Moreover, PA had the lowest CR value compared with the other groups (P < .05). This means PA was the most translucent material in this study. Rietveld refinement found that PA presented the greatest percentage of cubic phase, followed by TZI, ZI, and P, respectively. CONCLUSION. The different approaches are used by manufacturers to fabricate various types of translucent zirconia with different levels of translucency and mechanical properties, which should be concerned for material selection for successful clinical outcome.

• Journal of Powder Materials
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• v.15 no.1
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• pp.31-36
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• 2008

In this study, the bottom-up powder metallurgy and the top-down severe plastic deformation (SPD) techniques for manufacturing bulk nanomaterials were combined in order to achieve both full density and grain refinement without grain growth of rapidly solidified Al-20 wt% Si alloy powders during consolidation processing. Continuous equal channel multi-angular processing (C-ECMAP) was proposed to improve low productivity of conventional ECAP, one of the most promising method in SPD. As a powder consolidation method, C-ECMAP was employed. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructures of the ECMAP processed materials. It was found that effective properties of high strength and full density maintaining nanoscale microstructure are achieved. The proposed SPD processing of powder materials can be a good method to achieve fully density and nanostructured materials.

• Korean Journal of Materials Research
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• v.16 no.9
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• pp.592-597
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• 2006

A deoxidized low-phosphorous (DLP) copper was processed by accumulative roll-bonding (ARB) for ultra grain refinement and high strengthening. Two copper sheets 1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and roll-bonded by about 50% reduction rolling without lubrication at ambient temperature. The bonded sheet is then cut to the two pieces of same dimensions and the same procedure was repeated to the sheets up to eight cycles (${\varepsilon}{\sim}6.3$). TEM observation revealed that ultrafine grains were developed after the 4th cycle, and their size decreased at higher cycles. Tensile strength of the copper increased with the equivalent strain, and it reached 547 MPa which was 3 times higher than that of the initial material. It is concluded that the ARB process is an effective method for high strengthening of the DLP copper.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.26-31
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• 2007

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both real density and grain refinement of metallic powders. ECAP (Equal Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method. Effects of processing parameters on densification and density distributions were investigated.

• Design & Manufacturing
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• v.10 no.2
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• pp.34-38
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• 2016

In this paper, a transversely isotropic behavior of AZ31 Mg alloy produced by equal-channel angular pressing (ECAP) process was investigated through tensile test and microstructure observation. The effects of initial ECAP pass number on the anisotropic behavior and mechanical properties of the Mg alloy are evaluated after conventional direct extrusion test, which are carried out at a temperature of $200^{\circ}C$. As a result of the tensile test in three directions ($0^{\circ}$, $45^{\circ}$, and $90^{\circ}$ to the extrusion direction of the sheet) at room temperature, elongation of as-extruded AZ31 alloy(ECAP for 0 pass) showed an unusual anisotropic behavior depending on the extrusion direction although the yield strength and tensile strength are similar to the ECAPed AZ31 alloy. After ECAP for 4 passes at $200^{\circ}C$, microstructural observations of ECAPed magnesium alloy showed a significant grain refinement, which is leading to an equiaxed grain structure with average size of $2.5{\mu}m$. The microstructures of the extruded billet are observed by the use of an electron back-scattering diffraction (EBSD) technique to evaluate of the influence on the grain refinement during extrusion process and re-crystallization mechanism of AZ31 Mg alloy.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.1
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• pp.6-12
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• 2017

In this study tensile and impact properties of three hypo-eutectoid steels containing different micro-alloying elements were investigated in terms of microstructural factors such as pro-eutectoid ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness. Yield point phenomenon appeared in all the steel specimens during tensile testing, and ultimate tensile stress was mainly dependent on pearlite fraction. On the other hand, the refinement of austenite grain size caused by the addition of micro-alloying elements resulted in the increment of ferrite volume fraction and carbon contents in pearlite because of the refinement of pro-eutectoid ferrite grain size. As a result, cementite thickness in pearlite increased and had an effect on deteriorating the low temperature impact toughness.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.329-334
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• 2015

The aim of this paper is to determine the proper heat treatment temperature for SDSS tube production without ${\sigma}$-phase precipitation. When Mother steel tube was heat treated at $800^{\circ}C$ temperature, relatively a large amount of ${\sigma}$-phase precipitated and grain refinement of ferrite phase occurred simultaneously. However, in Pilgered and Drawn steel tubes, grain refinement of the ferrite phase did not occur and a small amount of ${\sigma}$-phase precipitated. For all three types of steel tubes, the pitting potential was reduced to 2/5 or less compared with the untreated one and corrosion also occurred in the salt spray test due to the precipitation of ${\sigma}$-phase. When heat treatment temperature was $900^{\circ}C$, grain refinement of the ferrite phase occurred and very little ${\sigma}$-phase precipitated in Pilgered and Drawn steel tubes. But when heat treatment was done at $1,000^{\circ}C$ temperature, all three types of steel tubes had a similar corrosion properties of that of untreated one and also corrosion did not occur in the salt spray test, as ${\sigma}$-phase did not precipitate. Therefore, the optimum heat treatment temperature range is determined to be more than $1000^{\circ}C$ for the SDSS at which corrosion does not occur.

• Journal of Powder Materials
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• v.8 no.3
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• pp.168-173
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• 2001

The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

• Korean Journal of Materials Research
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• v.22 no.6
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• pp.303-308
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• 2012

This study evaluated the enhancement of microstructural and mechanical properties of a cross rolled Ni-10Cr alloy, comparing with conventionally rolled material. Cold rolling was carried out to 90% thickness reduction and the specimens were subsequently annealed at $700^{\circ}C$ for 30 min to obtain a fully recrystallized microstructure. Cross roll rolling was carried out at a tilted roll mill condition of $5^{\circ}$ from the transverse direction in the RD-TD plane. In order to observe the deformed microstructures of the cold rolled materials, transmission electron microscopy was employed. For annealed materials after rolling, in order to investigate the grain boundary characteristic distributions, an electron back-scattering diffraction technique was applied. Application of cold rolling to the Ni-10Cr alloy contributed to notable grain refinement, and consequently the average grain size was refined from 135 ${\mu}m$ in the initial material to 9.4 and 4.2 ${\mu}m$ in conventionally rolled and cross rolled materials, respectively, thus showing more significantly refined grains in the cross rolled material. This refined grain size led to enhanced mechanical properties such as yield and tensile strengths, with slightly higher values in the cross rolled material. Furthermore, the <111>//ND texture in the CRR material was better developed compared to that of the CR material, which contributed to enhanced mechanical properties and formability.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.263-267
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• 2011

The present study was carried out to evaluate the microstructural and mechanical properties of cross-roll rolled pure copper sheets, and the results were compared with those obtained for conventionally rolled sheets. For this work, pure copper (99.99 mass%) sheets with thickness of 5 mm were prepared as the starting material. The sheets were cold rolled to 90% thickness reduction and subsequently annealed at $400^{\circ}C$ for 30 min. Also, to analyze the grain boundary character distributions (GBCDs) on the materials, the electron back-scattered diffraction (EBSD) technique was introduced. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets with an average size of 100 ${\mu}M$. In particular, the average grain size became smaller by cross-roll rolling (6.5 ${\mu}M$) than by conventional rolling (9.8 ${\mu}M$). These grain refinements directly led to enhanced mechanical properties such as Vickers micro-hardness and tensile strength, and thus the values showed greater increases upon cross-roll rolling process than after conventional rolling. Furthermore, the texture development of <112>//ND in the cross-roll rolling processed material provided greater enhancement of mechanical properties relative to the case of the conventional rolling processed material. In the present study, we systematically discuss the enhancement of mechanical properties in terms of grain refinement and texture distribution developed by the different rolling processes.