• Tribology and Lubricants
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• 제11권5호
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• pp.78-86
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• 1995

The silicon nitride based ceramic cutting tool materials have been fabricated by gas pressure sintering (GPS) or hot pressing (HP). Their mechanical properties were measured and the effect of the fabrication variables on the properties were examined. Also, effect of adding TiN or TiC particulates on the mechanical properties of the silicon nitride ceramics were investigated. Ceramic cutting tools (ISO 120408) were made of the sintered bodies. Cutting performance test were performed on either conventional or NC lathe. The workpieces were grey cast iron, hardened alloy steel (AISI 4140, HRc>60) and Ni-based superalloy (Inconel 718). The results showed that fabrication variables, namely, sintering temperature and time, exerted a strong influence on the microstincture and mechanical properties of the sintered body, which, however, did not make much difference in wear resistance of the tools. High hardness of the tool containing TiC particulates exhibited good cutting performance. Extensive crater wear was observed on both monolithic and TiN-containing silicon nitride tools after cutting the hardened alloy steel. Inconel 718 was extremely difficult to cut by the current cutting tools.

• 한국정밀공학회지
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• 제19권2호
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• pp.79-86
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• 2002

In end milling process the undeformed chip thickness and the cutting force components vary periodically with phase change of the tool. In this study, up end milling process is transformed to the equivalent oblique cutting. The varying undeformed chip thickness and the cutting force components in end milling process are replaced with the equivalent average ones. Then it can be possible to analyze the chip-tool friction and shear process in the shear plane of the end milling process by the equivalent oblique cutting system. According to this analysis, when cutting Inconel 718, 61, 64 and 55% of the total energy is consumed in the shear process with the helix angle 30$^{\circ}$, 40$^{\circ}$ and 50$^{\circ}$ respectively, and the balance is consumed in the friction process. With the helix angle of 40$^{\circ}$ the specific cutting energy consumed is smaller than with the helix angle 30$^{\circ}$ and 50$^{\circ}$.

• Journal of Welding and Joining
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• 제31권6호
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• pp.50-57
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• 2013

Characterization of microstructures and cryogenic mechanical properties of electro beam (EB) welds between cast and forged Inconel 718 superalloys has been investigated. Optimal EBW condition was found in the beam current range of 36~39 mA with the constant travel speed of 12 mm/s and arc voltage of 120 kV for 10 mm-thick specimens. Electron beam current lower than 25 mA caused to occur the liquation microfissuring in cast-side heat affected zone (HAZ) of EB welds. The HAZ liquation microfissure was found on the liquated grain boundaries with resolidified ${\gamma}/Laves$ and ${\gamma}/NbC$ eutectic constituents. EBW produced welds showing a fine dendritic structure with relatively discrete Laves phase due to fast cooling rate. After post weld aging treatment, blocky Laves phase and formation of ${\gamma}^{\prime}+{\gamma}^{{\prime}{\prime}}$ strengtheners were observed. Presence of primary strengthener and coarse Laves particles in PWHT weld may cause to reduce micro-plastic zone ahead of a crack, leading to a significant decrease in Charpy impact toughness at $-196^{\circ}C$. Fracture initiation and propagation induced by Charpy impact testing were discussed in terms of the dislocation structures ahead of crack arisen from the fractured Laves phase.

• 한국재료학회지
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• 제8권4호
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• pp.354-358
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• 1998

Inconel 719 선재의 경도에 미치는 냉간신선가공량과 시효시간의 영향을 경도측정과 전자현미경을 사용하여 조사하였다. 고용화처리된 재료의 경도는 245Hzv이었으나 50% 냉간신선가공으로 450Hv까지 증가했다. 경도값은 시효시간이 증가함에 따라 초기에 증가하다 감소하는 것으로 나타났으며, 시효 초기 경도증가는 $\gamma^{"}$과 $\gamma^{'}$ 상의 석출에 의한 것이며, 최고경도 이후의 경도감소는$\gamma^{'}$상이 $\delta$상으로 변태되었기 때문이다. 냉간가공도가 증가함에 따라 최고경도에 이르는 시간은 감소되어 0, 30, 50%가공재들에 대해 각각 30, 10, 5분으로 나타났다. 이는 냉간가공으로 인해 $\gamma^{'}$ / $\gamma^{'}$ 상의 석출이 촉진되었기 때문이다. 50%가공재의 경우 1116K에서 5분 시효로$\Upsilon^{'}$ 및 $\Upsilon^{'}$상들이 석출되었다. 또한 50%가공재에서는 초기경도 이하로 경도값이 감소되었는데, 이와 같은 경도값의 큰 감소는 재결정이 일어났기 때문이다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.308-313
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• 2002

In end milling process, the undeformed chip section area and cutting forces vary periodically with phase change of the tool. However, the real undeformed chip section area deviates from the geometrically ideal one owing to cutter runout and tool shape error. In this study, a method of estimating the real undeformed chip section area which reflects cutter runout and tool shape error was presented during down end-milling of Inconel 715 using measure cutting forces. Contrary to the up-end milling the value of radial specific cutting resistance, $K_r$, becomes larger as the helix angle increases from $30^{\circ}$ to $40^{\circ}$ and it shows almost same value at $50^{\circ}$ The value of tangential specific cutting resistance, $K_t$ becomes larger as the helix angle increases same as in up-end milling, the $KK_r$, and $K_t$ values show a tendency to decrease with increase of the modified chip section area and this tendency is distinct with helix angle $40^{\circ}$.

• Corrosion Science and Technology
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• 제12권1호
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• pp.7-11
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• 2013

High velocity oxy-fuel (HVOF) spray coating of WC-metal powder (powder) was carried out to improve the resistances of friction, wear and corrosion of magnetic bearing shaft material Inconel718 (In718) of turbo blower. A micron sized WC-metal powder (86.5% WC, 9.5% Co 4% Cr) was coated onto In718 surface using HVOF thermal spraying. During the spraying, the binder metals and alloy such as Co, Cr and Co-Cr alloy were molten and a small portion of WC particles were partially decomposed to $W_2C$ and free carbon at above its decomposition temperature of $1250^{\circ}C$. The free carbon and excessively sprayed oxygen formed carbon oxide gases, resulting a porous coating of porosity of $2.2{\pm}0.3%$. The surface hardness of substrate increased approximately three times from 400 Hv of In718 to $1260{\pm}30Hv$ of the coating The friction coefficients of the coating were approximately $0.33{\pm}0.03$ at $25^{\circ}C$ and $0.26{\pm}0.03$ at $450^{\circ}C$. These values were smaller than those of In718 substrate at both temperatures due to the lubrication from the free carbon and the cobalt oxide debris. The corrosion resistance of the coating was higher than that of In718 both in salt water of 3.5% NaCl and acid of 1 M HCl solutions, on the contrary, it was lower in base solution of 1 M NaOH. According to this study, the HVOF WC-metal powder coating is recommended for the durability improvement of magnetic bearing shaft of turbo blower.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2008년도 추계학술대회 초록집
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• pp.11-12
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• 2008

Micron-sized Co-alloy T800 powder was coated on Inconel718 (IN718) using high velocity oxygen fuel (HVOF) thermal spraying by the optimal coating process (OCP) determined from the best surface hardness of 16 coatings prepared by Taguchi program. The surface hardness improved 140-160 % from 399 Hv of IN718 to 560-630 Hv by the coating. Porosity of the coating was 1.0-2.7 %, strongly depending on spray parameters. Both friction coefficients (FC) and wear traces (WT) of the coating were smaller than those of IN718 substrate at both $25^{\circ}C$ and $538^{\circ}C$. FC and WT of IN718 and coating decreased with increasing the surface temperature. Tensile bond strength (TBS) and fracture location (FL) of Ti64/T800 were 8,770 psi and near middle of T800 coating respectively. TBS and FL of Ti64/NiCr/T800 were 8,740 psi and near middle of T800 coating respectively. This showed that cohesion of T800 coating was 8,740-8,770 psi, and adhesion of T800 on Ti64 and NiCr was stronger than the cohesion of T800.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.245-247
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• 2001

In this study, the effects of dilution on the wear behavior of PTAW (Plasma Transferred Arc Welding) Inconel 625, Inconel 718 and Stellite 6 overlays on Nimonic 80A were investigated. Inorder to evaluate the wear performance, two-body and three-body abrasive wear test, and dry sliding wear test were performed. According to wear tests, the wear rate of deposit with dilution 30% was higher than that of dilution 10% by 10%, and it was also found the plastic deformation near worn surface.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.174-176
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• 2005

• 한국표면공학회지
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• 제24권3호
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• pp.151-161
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• 1991

The isothermal oxidation behaviour of commercial superalloys produced in Korea was investigated by using Cahn-2000 microbalance in air at $1000^{\circ}C$ and $1100^{\circ}C$. The effect of alloying elements on the isothermal oxidation was studied by examination of the oxide structures, their morphologies, and EDS linescanning and mapping of cross-section of oxidized specimens. Generally, external Cr2O3 films were formed on all alloy surface, but were not pure, The effect on the oxidation behaviour of refractory elements such as Nb, Mo in Inconel 718 was considered to be deleterious, and the formation of internal Al oxide in Inconel 601 was beneficial.