• Transactions of Materials Processing
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• v.8 no.3
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• pp.233-233
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• 1999

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.221-225
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• 2015

The sintering effect on the microstructure, electrical properties, and dielectric characteristics of ZnO-V₂O₅-MnO₂-Nb₂O₅-Dy₂O₃-based ceramics was investigated. With the increase of sintering temperature from 875 to 950℃, the density of the sintered pellets decreased from 5.57 to 5.45 g/cm³ and the average grain size increased from 4.3 to 10.9 μm. The breakdown field decreased noticeably from 6,095 to 996 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900℃ exhibited the best nonlinear properties: 39.2 in the nonlinear coefficient and 0.24 mA/cm² in the leakage current density. The dielectric constant increased sharply from 658.6 to 2,928.8 with the increase of sintering temperature. On the whole, the dissipation factor exhibited a fluctuation with the increase of the sintering temperature, and a minimum value of 0.284 at 900℃.

• Journal of Powder Materials
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• v.15 no.6
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• pp.471-476
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• 2008

Sintered Nd-Fe-B magnets have been widely used due to their excellent magnetic properties, especially for driving motors of hybrid and electric vehicles. The microstructure of Nd-Fe-B magnets strongly affects their magnetic properties, in particular the coercivity. Therefore, a post-sintering process like heat-treatment is required for improving the magnetic properties of Nd-Fe-B sintered magnets. In this study, cyclic heat treatment was performed at temperatures between $350^{\circ}C$ and $450^{\circ}C$ up to 16 cycles in order to control microstructures such as size and shape of the Nd-rich phase without grain growth of the $Nd_{2}Fe_{14}B$ phase. The 2 cycles specimen at this temperature range showed more homogeneous microstructure which leads to higher coercivity of 35 kOe than as-sintered one.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.498-505
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• 2010

Wrought magnesium alloys show a low formability at room temperature, and a remarkable anisotropy of mechanical properties make it difficult to use them in a deformation process in industry. The microstructure and crystallographic texture of metals are developed during thermo-mechanical processes, and they are significant to the understanding of the mechanical properties of metals. This work studies the microstructure, texture development and tensile properties of the extruded AZ31 Mg alloy after rolling at 100 and $300^{\circ}C$. After 40% rolling at $100^{\circ}C$, many deformed twins were observed and a relatively weak texture developed. The basal poles were split and rotated towards the rolling direction about $20^{\circ}$. During 60% rolling at $300^{\circ}C$, the dynamic recrystallization (DRX) took place and developed a strong <0001>II ND fiber texture, which influenced the poor formability at room temperature.

• International Journal of Precision Engineering and Manufacturing-Green Technology
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• v.5 no.5
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• pp.605-612
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• 2018

This work investigates the relationships between the static mechanical properties of Ti-6Al-4V manufactured through selective laser melting (SLM) and post-process heat treatments, namely stress relieve, annealing and hot isostatic pressing (HIP). In particular, Ti-6Al-4V parts were fabricated in three different build orientations of X, Z, and $45^{\circ}$ to investigate the multi-directional mechanical properties. The results showed that fully densified Ti-6Al-4V parts with densities of up to 99.5% were obtained with optimized SLM parameters. The microstructure of stress relieved and mill annealed samples was dominated by fine ${\alpha}^{\prime}$ martensitic needles. After HIP treatment, the martensite structure was fully transformed into ${\alpha}$ and ${\beta}$ phases (${\alpha}+{\beta}$ lamellar). Within the realm of tensile properties, the yield and ultimate strength values were found statistically similar with respect to the built orientation for a given heat treatment. However, the ductility was found orientation dependent for the HIP samples, where a lower value was observed for samples built in the X direction.

• Journal of the Korean institute of surface engineering
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• v.54 no.3
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• pp.133-138
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• 2021

Ternary Ti-X-N coatings, where X = Al, Si, Cr, O, etc., have been widely used for machining tools and cutting tools such as inserts, end-mills, and etc. Ti-Al-N-O coatings were deposited onto silicon wafer and WC-Co substrates by a cathodic arc evaporation (CAE) technique at various negative substrate bias voltages. In this study, the influence of substrate bias voltages during deposition on the microstructure and mechanical properties of Ti-Al-N-O coatings were systematically investigated to optimize the CAE deposition condition. Based on results from various analyses, the Ti-Al-N-O coatings prepared at substrate bias voltage of -80 V in the process exhibited excellent mechanical properties with a higher compressive residual stress. The Ti-Al-N-O (-80 V) coating exhibited the highest hardness around 30 GPa and elastic modulus around 303 GPa. The improvement of mechanical properties with optimized bias voltage of -80 V can be explained with the diminution of macroparticles, film densification and residual stress induced by ion bombardment effect. However, the increasing bias voltage above -80 V caused reduction in film deposition rate in the Ti-Al-N-O coatings due to re-sputtering and ion bombardment phenomenon.

• Corrosion Science and Technology
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• v.22 no.1
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• pp.30-35
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• 2023

Hafnium nitride (HfN) thin films were fabricated by mid-frequency magnetron sputtering (mfMS) and direct current magnetron sputtering (dcMS) and their mechanical and structural properties were compared. In particular, changes in the HfN film properties were observed by changing the pulse frequency of mfMS between 5 kHz, 15 kHz, and 30 kHz. The crystalline structure, microstructure, 3D morphology, and mechanical properties of the HfN films were compared by x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and nanoindentation tester, respectively. HfN film deposited by mfMS showed a smoother and denser microstructure as the frequency increased, whereas the film deposited by dcMS showed a rough and sloppy microstructure. A single δ-HfN phase was observed in the HfN film made by mfMS with a pulse frequency of 30 kHz, but mixed δ-HfN and HfN_0·4 phases were observed in the HfN film made by dcMS. The mechanical properties of HfN film made by mfMS were improved compared to film made by dcMS.

• Transactions of Materials Processing
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• v.32 no.3
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• pp.145-152
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• 2023

The Inconel 706 alloy is a nickel-based super alloy and requires a large load for hot forging due to its excellent mechanical properties at high temperature. Rotary forging process is an innovative metal forging process where workpiece is gradually deformed by the revolving conical upper die with an inclination angle. This process allows that the workpiece is partially in contact with an upper die during the process so that the press force is considerably lower compared with the conventional upsetting process. In this study, experiments of rotary forging process and conventional upsetting process for cylindrical parts using Inconel 706 where conducted to investigate the formability of rotary forging process. And microstructure analysis and mechanical properties of Inconel 706 were performed to investigate the effect of rotary forging process on the material property.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.5
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• pp.285-297
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• 2023

The effects of aging treatment sequence, specifically pre-aging and post-aging, on the microstructure and mechanical properties of Al-Zn-Mg-Cu aluminum alloys has been studied in comparison to symmetrically rolled specimens. In symmetrically rolled specimens, a straight-band precipitation distribution was observed, whereas asymmetrically rolled specimens exhibited a curved-band microstructure of fine precipitates. Notably, the asymmetrically rolled specimens displayed higher strengths. In the case of post-aging, the aging process occurred after rolling, and the dislocations generated during rolling acted as nucleation sites for precipitates during aging. This resulted in the formation of fine precipitates, contributing to improved mechanical properties compared to symmetric rolling. To enhance strength of the Al-Zn-Mg-Cu aluminum alloys, asymmetric rolling proves to be more effective than symmetric rolling, with post-aging showing greater efficacy than pre-aging.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.68-74
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• 2015

To compare the microstructure and electrochemical properties between two binary alloys (Cr-Si, Ni-Si), two composition of binary alloys with the same capacity were selected using phase-diagram and prepared by matrix-stabilization method to suppress the volume expansion of Si by inactive-matrix. Master alloys were made by Arc-melting followed by fine structured ribbon sample preparation by Rapid Solidification Process (RSP, Melt-spinning method) under the same conditions. Also powder samples were produced by wet grinding for X-Ray Diffraction (XRD) and electrochemical measurements. As predicted from the phase diagram, only active-Si and inactive-matrix ($CrSi_2$, $NiSi_2$) were detected. The results of Scanning Electron Microscope (SEM) and Transmission Electron Microscopy - Energy Dispersive X-ray Spectroscopy (TEM-EDS) show that Cr-Si alloy has finer microstructure than Ni-Si alloy, which was also predictable through phase diagram. The electrochemical properties related to microstructure were evaluated by coin type full- and half-cells. Separately, self-designed test-cells were used to measure the volume expansion of Si during reaction. Volume expansion of Cr-Si alloy electrode with finer microstructure was suppressed significantly and improved in cycle capability, in comparison Ni-Si alloy with coarse microstructure. From these, we could infer the correlation of microstructure, volume expansion and electrochemical degradation and these properties might be predicted by phase diagram.