• Korean Journal of Materials Research
• /
• v.30 no.12
• /
• pp.672-677
• /
• 2020

Expensive PCBN or ceramic cutting tools are used for the processing of difficult-to-cut materials such as Ti and Ni alloy materials. These tools have a problem of breaking easily due to their high hardness but low fracture toughness. To solve this problem, cutting tools that form various coating layers are used in low-cost WC-Co hard material tools, and researches on various tool materials are being conducted. In this study, WC-5, 10, and 15 wt%Ni hard materials for difficult-to-cut cutting materials are densified using horizontal ball milled WC-Ni powders and pulsed current activated sintering method (PCAS method). Each PCASed WC-Ni hard materials are almost completely dense, with a relative density of up to 99.7 ~ 99.9 %, after the simultaneous application of pressure of 60 MPa and electric current for 2 min; process involves almost no change in the grain size. The average grain sizes of WC and Ni for WC-5, 10, and 15 wt%Ni hard materials are about 1.09 ~ 1.29 and 0.31 ~ 0.51 µm, respectively. Vickers hardness and fracture toughness of WC-5, 10, and 15 wt%Ni hard materials are about 1,923 ~ 1,788 kg/mm2 and 13.2 ~ 14.3 MPa.m1/2, respectively. Microstructure and phase analyses of PCASed WC-Ni hard materials are performed.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.05a
• /
• pp.23-28
• /
• 2002

This paper describes the machining characteristics of the $MoSi_2$ based composites by electric discharge drilling with various tubular electrodes, besides, Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $MoSi_2$ -based composites has been developed in new materials for jet engine of supersonic-speed airplanes and gas turbine for high- temperature generator. Achieving this objective may require new hard materials with high strength and high temperature-resistance. However, With the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. By combining a nonconducting ceramics with more conducting ceramic it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like (Nb, Mo)$SiO_2$ and $Nb_2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature. $MoSi_2$ composites which a hole drilling was not possible by the conventional machining process, enhanced the capacity of ED-drilling by adding $NbSi_2$ relative to that of SiC or $ZrO_2$ reinforcements.

• The Korean Journal of Ceramics
• /
• v.2 no.4
• /
• pp.216-220
• /
• 1996

In the present paper, a new type of DC arc plasma torch is disclosed. The principles of the new magnetic and fluid dynamic controlled large orifice long discharge tunnel plasma torch is discussed. Two series of DC Plasma Jet diamond film deposition equipment have been developed. The 20kW Jet equipped with a $\Phi$70 mm orifice torch is capable of deposition diamond films at a growth rate as high as 40$\mu\textrm{m}$/h over a substrate area of $\Phi$65 mm. The 100kW high power Jet which is newly developed based on the experience of the low power model is equipped with a $\Phi$120 mm orifice torch, and is capable of depositing diamond films over a substrate area of $\Phi$110 mm at growth rate as high as 40 $\mu\textrm{m}$/h, and can be operated at gas recycling mode, which allows 95% of the gases be recycled. It is demonstrated that the new type DC plasma torch can be easily scaled up to even higher power Jet. It is estimated that even by the 100kW Jet, the cost for tool grade diamond films can be as low as less than ＄4/carat.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1998.04b
• /
• pp.6-6
• /
• 1998

In 1957, the first magnetic disk drive compatible with a movable head was introduced as an external file memory device for computer system. Since then, magnetic disks have been improved by increasing the recording density, which has brought about the development of a high performance thin film magnetic head. The thin film magnetic head has a magnetic circuit on a ceramic substrate using IC technology. The physical property of the substrate material is very important because it influences the tribology of head/disk interface and also manufacturing process of the head. $Al_{2}O_{3}$-TiC ceramics, so called ALTIC, is known to be one of the best substrate materials which satisfies this property requirement. Even though the head is not in direct contact with the disk, frequent instantaneous contacts are unavoidable due to its high rotating speed and the close gap between them. This may cause damage in the magnetic recording media and, thus, it is very important that the magnetic head has a good wear resistance. $Al_{2}O_{3}$-TiC ceramics has an excellent tribological property in head/disk interface. Manufacturing process of thin film head is similar to that of IC, which requires extremely smooth and flat surface of the substrate. The substrate must be readily sliced into the heads without chipping. $Al_{2}O_{3}$-TiC ceramics has excellent machineability and mechanical properties. $Al_{2}O_{3}$-TiC ceramics was first developed at Nippon Tungsten Co. as cutting tool materials in 1968, which was further developed to be used as the substrate materials for thin film head in collaboration with Sumitomo Special Metals Co., Ltd. in 1981. Today, we supply more than 60% of the substrates for thin film head market in the world. In this paper, we would like to present the sintering process of $Al_{2}O_{3}$-TiC ceramics and its property in detail.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.18 no.2
• /
• pp.113-118
• /
• 2002

Conventional radiograph, computed tomograph (CT), magnetic resonance image (MRI) are commonly used methods for diagnosis of oro-maxillofacial cancer. MRI is an effective tool to verify soft tissue lesion however, metal produces black artifacts in the image. Therefore, metal structure should be removed before taking MRI to diagnose head and neck cancer patients. A 52-year-old female patient with adenocarcinoma in the posterior right soft palate was referred to take a MRI before surgery. She has 7-unit porcelain fused to metal bridge in the maxilla. Eight-unit Tagis-Vectris fixed partial denture was fabricated to replace her existing PFM bridge to take a MRI without any artifact before and after surgery. The patient satisfied with her restorations in terms of esthetics, function after 11 months. Even though minor staining was detected, Tagis-Vectris restoration fixed partial denture was intact during observation period.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.10
• /
• pp.41-49
• /
• 2013

This paper suggests the dielectric resonator antenna using LTCC process for mm-wave car radar system. In this paper, dielectric resonator antennas (DRA) operated in 76-77 GHz frequency band are designed. And, using the LTCC process, the structures of dielectric resonator with SRR (split ring resonator) inside and those of dielectric resonator with probe inside are suggested. Linear polarization antennas and circular polarization antenna are designed for the DRA with probe inside. Three kinds of the DRA antennas are designed and their characteristics are calculated using CST RF simulation tool. The designed antennas are fabricated and measured and the measured results are compared with calculated results. The measured operating frequencies of DRAs are within 76 GHz to 77 GHz, which are close to the calculated results, and the measured gains are about 8.15 dBi to 10.82 dBi.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.135-135
• /
• 1999

It is well known that Raman spectroscopy is powerful tool in analysis of sp3/sp3 bonding fraction in diamond-like carbon(DLC) films. Raman spectra of DLC film is composed of D-peak centered at 1350cm-1 and G-peak centered at 1530cm-1. The sp3/sp3 fraction is qualitatively acquired by deconvolution method. However, in case of DLC film, it is generally observed that G-peak position shifts toward low wavenumber as th sp3 fraction increases. However, opposite results were frequently observed in ta-C films. ta-C film has much higher residual compressive stress due to its high sp3 fraction compared to the DLC films deposited by CVD method. Effect of residual stress on G-peak position is most recommendable parameter in Raman analysis of ta-C, due to its smallest fitting error among many parameters acquired by peak deconvolution of symmetric spectra. In current study, the effect of residual stress on Raman spectra was quantitatively evaluated by free-hang method. ta-C films of different residual stress were deposited on Si-wafer by modifying DC-bias voltage during deposition. The variation of the G-peak position along the etching depth were observed in the free-hangs of 20~30${\mu}{\textrm}{m}$ etching depth. Mathematical result based on Airy stress function, was compared with experimental results. The more reliable analysis excluding stress-induced shift was possible by elimination of the Raman shift due to residual compressiove stress.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.6
• /
• pp.1465-1477
• /
• 1993

Powder Injection Molding(PM) is an advanced and complicated technology for manufacturing ceramic or metal products making use of a conventional injection molding process, which is generally used for plastic products. Among many technologies involved in the successful PIM, injection molding process is one of the key steps to form a desired shape out of powder/binder mixtures. Thus, it is of great importance to have a numerical tool to predict the powder injection molding filling process. In this regard, a finite element analysis system has been developed for numerical simulations of filling process of powder injection molding. Powder/polymer mixtures during the filling pro cess of injection molding can be rheologically characterized as Non-Newtonian fluids with a so called yield phenomena and have a peculiar feature of apparent slip phenomena on the wall boundaries surrounding mold cavity. Therefore, in the present study, a physical modeling of the filling process of powder/polymer mixtures was developed to take into account both the yield stress and slip phenomena and a finite element formulation was developed accordingly. The numerical analysis scheme for filling simulation is accomplished by combining a finite element method with control volume technique to simulate the movement of flow front and a finite difference method to calculate the temperature distribution. The present study presents the modeling, numerical scheme and some numerical analysis results showing the effect of the yield stress and slip phenomena.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.6
• /
• pp.1-6
• /
• 2017

Recently, the brittle materials such as ceramics, glass, sapphire and textile material have been widely used in semiconductors, aerospace and automobile owing to high functional characteristics. On the other hand, it has the characteristics of difficult-to-cut material relative to all materials. In this study, diamond electro-deposited band-saw machine was developed to operate stably using water-coolant type through relative motion between band-saw tool and $Al_2O_3$ material. High densified $Al_2O_3$ material was manufactured by spark plasma sintering method. The bulk density was observed by the Archimedes law and the theoretical density was estimated to be $3.88g/cm^3$ and its hardness 14.7 MPa. From the dicing sawing test of $Al_2O_3$ specimen, behavior of surface roughness and band-saw wear are dominantly affected by the increase of the band-saw linear velocity. Additionally, an continuous pattern type of diamond band-saw was a very effective due to entry impact as a one-off for brittle material.

• Korean Journal of Materials Research
• /
• v.31 no.7
• /
• pp.392-396
• /
• 2021

Expensive PCBN or ceramic cutting tools are used for processing of difficult-to-cut materials such as Ti and Ni alloy materials. These tools have the problem of breaking easily due to their high hardness but low fracture toughness. To solve these problems, cutting tools that form various coating layers are used in low-cost WC-Co hard material tools, and research on various tool materials is being conducted. In this study, binderless-WC, WC-6 wt%Co, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are densified using horizontal ball milled WC-Co, WC-Co-Mo₂C powders, and spark plasma sintering process (SPS process). Each SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are almost completely dense, with relative density of up to 99.5 % after the simultaneous application of pressure of 60 MPa and almost no significant change in grain size. The average grain sizes of WC for Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are about 0.37, 0.6, 0.54, and 0.43 ㎛, respectively. Mechanical properties, microstructure, and phase analysis of SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are investigated.