• 한국재료학회:학술대회논문집
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• 한국재료학회 1997년도 한국재료학회 추계학술발표회
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• pp.174-174
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• 1997

• 한국재료학회지
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• 제12권4호
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• pp.308-316
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• 2002

The cavitation erosion behavior of wear-resistant hardfacing alloys such as Co-base Stellite 6, Fe-base Norem 02 and new Fe-base alloy were investigated up to 50 hours by using a 20kHz vibratory cavitation erosion test equipment. The crack, initiated easily at the interfaces between matrix and hard second phase, was repressed effectively in Stellite 6 because the matrix was hardened by phase transformation. For this reason, Stellite 6 showed an excellent cavitation erosion resistance compared to Norem 02. The phase transformation also occurred in Norem 02, but the increase of volume fraction of the interfaces caused the crack to be initiated frequently, thus resulting in a 1arge material loss. The matrix of NewAlloy was hardened effectively by vlongrightarrow$\alpha$' phase transformation and the volume fraction of the interfaces was very small compared to Norem 02. This caused the propagation of crack to the matrix to be repressed effectively. Therefore, NewAlloy showed a very excellent cavitation erosion resistance. It wasn't considered that the cavitation erosion resistance of NewAlloy was influenced the temperature of the bath filled with a distilled water up to $80^{\circ}C$.

• 한국재료학회지
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• 제9권2호
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• pp.199-204
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• 1999

As the engine design change to get high efficiency and performance of commercial diesel engine, surface wear of the cam follower becomes an important issues as applied load increasing at the contact face between cam follower and cam. Purpose of this study is the developing of the ceramic cam follower made of silicon nitride ceramic which is more wear resistant than the cast iron and sintered cam follower. Ceramic cam follower was made by direct brazing of thin ceramic disk to steel can follower body using active bracing alloy. Effect of joining condition on the interfacial phases and joining strength wer examined at bvarious joining temperatures, times, and cooling rates. Crowning resulted from the difference of thermal expansion coefficient after direct brazing without using any stress-relieving inter layer was measured. Interfacial phases are mainly titanium silicide and titanium nitride which are the products between active metal(Ti) in brazing alloy and silicon nitiride. Maximum joining strength of the ceramic metal joint, measured by DBS method, was 334MPa. Crowning(R) of the prototype ceramic cam follower was 1595mm. As machining for crowning is not necessary, production cost can be reduced.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1475-1484
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• 2003

The EDM processing characteristics of one of the nickel-based heat resistant alloys, Hastelloy- X, were investigated under the various EDM conditions and analyzed in terms of surface integrity. This alloy is commonly used as a material for the hot gas path component of gas turbines and it is difficult to machine by conventional machining methods. The primary EDM parameter which was varied in this study were the pulse-on time. Since the pulse-on time is one of the main factors that determines the intensity of the electrical discharge energy, it was expected that the machining ratio and the surface integrity of the specimens would be proportionally dependent on the pulse-on duration. However, experimental results showed that MRR (material removal rate) and EWR (electrode wear rate) behaved nonlinearly with respect to the pulse duration, whereas the morphological and metallurgical features showed rather a constant trend of change by the pulse duration. In addition the heat treating process affected the recast layer and HAZ to be recrystallized but softening occurred in recast layer only. A metallurgical evaluation of the microstructure for the altered material zone was also conducted.

• 한국정밀공학회지
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• 제25권12호
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• pp.47-54
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• 2008

Hard turning process can be defined as a single-point machining process carried out on "hard" materials. The process is intended to replace or limit traditional grinding operations that are expensive, environmentally unfriendly, and inflexible. The purpose of this study is to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, tool wear shape and chip formation by the outer cutting of a kind of wear resistant tungsten carbide V30. Hard turning experiments were carried out on this alloy using the PCD (Poly Crystalline Diamond), cBN (cubic Boron Nitride) and PcBN (Polycrystalline cubic Boron Nitride) cutting tools. The PcBN and the usual cBN tools were used to be compare with the PCD tool and the dry turning was carried out. The PcBN is attractive as the tool material which replaces the PCD. The tool wear width and cutting force were measured, and the worn tool and chip were observed. The difference of the tool wear mechanism among the three tool materials was investigated.

• 한국표면공학회지
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• 제25권3호
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• pp.107-116
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• 1992

The optimum thickness of Pd-Ni plated layers used as an electrical contact film was investigated by evaluating mechanical, thermal and environmental characteristics. The variations of morphologies and chemical compositions were studied by using SEM, EDS and ESCA. As a result of wear test, the wear resistance behavior of the gold plated layers was not changed with the sliding velocity changes. The palladium-nickel plated layer showed better wear resistance than the gold plated layer at low sliding velocity, but it showed poor wear resistance at high sliding velocity. Under the thermal condition of $400^{\circ}C$ in air, the gold thickness of $2\mu\textrm{m}$ without underplate on phosphorous bronze formed copper oxide on the surface layer by rapid diffusion of copper whereas the gold thickness of $0.8\mu\textrm{m}$ deposited on nickel and palladium-nickel underplate was stable at $400^{\circ}C$. Under the sulfur dioxide environments, the gold thickness of $0.3\mu\textrm{m}$ deposited on the nickel thickness of$ 3\mu\textrm{m}$ and the palladium-nickel thickness of $2\mu\textrm{m}$ underplate was more corrosion-resistant than the gold thickness of $2\mu\textrm{m}$ without underplate on phosphorous bronze. Under the nitric acid vapor environment, corrosion resistance of the gold film was superior to an equivalent thickness of the palladium-nickel film.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.172-178
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• 2001

Titanium alloys have lightness, high strength and good corrosion resistant characteristics, and broadly used in manufacturing parts for military and aerospace industries. And these alloys also are recognized for organism materials comparatively and used as fixing ones in the human body. Nevertheless thess alloys have excellent properties such as corrosion resistance, heat resistance, and good tensile strength, it is difficult to machine by traditional methods because of high hardness and chemically activated property. So higher tool wear is expected when cutting by tools. Therefore, it is required nontraditional machining process. And the mechanical characteristics such as surface structure and shape, hardness and bending strength are studied for wire electrical discharge machined and surface ground titanium alloys for various heat-treated conditions.

• 한국표면공학회지
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• 제32권3호
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• pp.265-275
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• 1999

Titanium nitride and related overlayers produced by arc ion plating (AIP) are applied as commercial coatings in world-wide scale since the middle of 80s. Due to the achievements of low temperature deposition (LTD), they begin now to be used as wear and corrosion-resistant coatings for machine parts, besides applications on cemented carbide and high speed steel cutting tools. On the other side, TiN can be now applied successfully to brass, Al-alloy, ZnAl alloy articles as decorative coating through LTD. Various nitrides, carbonitrides, borides and other refractory compounds, such as (Ti, Al)N, TiCN, CrN, are used as the coatings for special heavy-duty working conditions instead of TiN since 90s. More and more multilayer coatings are applied now substituting single layer ones. Duplex processes are under development.

• 소성∙가공
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• 제28권3호
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• pp.123-129
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• 2019

Hypereutectic Al-Si alloys have been widely utilized for wear-resistant components in the automotive industry. In order to expand the application of Hypereutectic Al-Si alloys, the addition of alloying elements forming a stable precipitate at high temperature is required. Thermally stable inter metallic compounds can be formed through the addition of transition elements such as Fe, Ni to Al alloys. However, the amount of transition element to be added to Al alloys is limited due to their low solid solubility. Also, hypereutectic Al-Si-Fe alloys form coarse primary Si phases and needle-shaped intermetallic compounds during solidification in the general casting processes. In this study, the effects of the destruction of Intermetallic compound and Si phase are investigated via hot extrusion. Both the microstructure and mechanical properties are discussed under different extrusion conditions.

• Tribology and Lubricants
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• 제30권4호
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• pp.240-245
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• 2014

Low alloy heat resistant brake disk and sintered brake pad are applied to mechanical brake system for the speed-up of urban rapid transit. In this research, we analyzed how the frictional characteristics between brake disk and pad are influenced by the disk mass. At a high disk mass, the friction stability was the lower value as a result of the lack of tribofilm formation at the disk surface. Wear rates of friction materials showed the higher value at a low disk mass and wear rates of 10 mm and 15 mm showed the similar level. Average friction coefficient was the lower value at the 10 mm disk thickness and range of variation of average friction coefficient was also the smaller value at the 10 mm disk thickness. However, there were no significant changes in the friction coefficients under any of test conditions. Surface roughness of a disk showed the highest value at the 5 mm disk and surface roughnesses of 10 mm and 15 mm showed the similar level. As a result, friction characteristics of disk mass influenced the friction stability, as well as the wear rate of friction pad and disk, but not the friction coefficient.