• 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.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.193-200
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• 2000

Si$_3$N$_4$powder with 2 wt% $Al_2$O$_3$and 6 wt% $Y_2$O$_3$additives was sintered by the gas pressure sintering (GPS) technique. The unlubricated wear behavior depending on sintering conditions such as sintering temperature, pressure, and sintering time was investigated. When the sintering temperature and time increased, the larger elongated grains were formed and the microstructural heterogeneity increased. When sintering pressure increased, grain growth, however, was impeded. Also, the wear properties depended on microstructure and friction coefficient were related to grain size. Based on the experimental results, the wear properties were associated with initial friction coefficients as well as mechanical properties including fracture toughness and flexural strength.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.218-221
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• 2004

Dry sliding wear behavior of electro-pressure sintered Co, $Co-20\;wt.\%$ CuSn and $Co-20\;wt.\%$ WC composites were investigated. Wear tests of the materials were carried out using a pin-on-disk wear tester at various loads of 10N-100N under a constant sliding speed condition of 0.38m/s against glass ($83\%\;SiO_2$) beads. Sliding distances were varied with a range of $100m{\sim}600m$. A scanning electron microscopy was used to examine morphologies of worn surfaces, cross-sections, and wear debris. The $Co-20\;wt.\%$ WC composite had the highest and the $Co-20\;wt.\%$ CuSn composite showed the lowest wear resistance among the tested materials. All specimens exhibited low friction coefficients ranging from 0.12 to 0.4 at the applied load of 100N.

• 한국분말재료학회지
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• 제11권6호
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• pp.451-461
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• 2004

Dry sliding wear behavior of electro-pressure sintered Co-Fe and Co-Ni compacts was investigated. Pin-on-disk wear tests were performed on the sintered Co-Fe, Co-Ni disks against alumina $(Al_2O_3)$ and silica $(SiO_2)$ balls at various loads ranging from 3N to 12N. A constant sliding speed of 0.1m/sec was employed. Wear rate was calculated by dividing the weight loss of a specimen by the measured specific gravity and sliding dis-tance. Worn surfaces and cross-sections of the specimens were examined using an SEM and EDS to investigate wear mechanism of the compacts. The wear behavior of the compacts were discussed as a function of their com-position. Effects of mechancial properties of the compact as well as oxide layers formed on wearing surface on the wear were also discussed.

• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.139-146
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• 2000

The development of high performance materials is very important subject in order to enhance the properties of bearings whose role is to transfer energy harmoniously by reducing the problem of friction and wear down, etc. between the interacting solid surfaces in relative motion under high loads in comply with mechanical operating mechanism of engines. In this study, several (100-x)Al-xSn coating films (where x=85, 75, 65 atomic % at Al) on substrates which are abt. 2mm thickenss of Kelmet layer sintered back steel were prepared by using RF sputtering system. These coating films were observed the morphology by SEM(Scanning Electron Microscope) and investigated the crystal structure by XRD(X-ray Diffractor) for their properties. And friction coefficient of these films was measured by ball-on-disc tester for their tribological properties. From the experimental results, it was shown that high performance properties of bearing can be improved greatly by controlling the composition and morphology of material surface with effective use of the plasma-assisted sputtering process.

• The Korean Journal of Ceramics
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• 제3권1호
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• pp.47-51
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• 1997

The dense sintered bodies of Si/SiC composite with various Si contents could be fabricated by changing the green density in the forming process. The Si/SiC/graphite composites with various graphite contents could be also fabricated by changing a graphite content in the starting composition. Their mechanical and tribological properties were characterized and wear mechanism was also studided. The hardness and strength of the Si/SiC and the Si/SiC/graphite were decreased with increasing the contents of free Si and graphite, respectively. However, the friction coefficient and specific wear rate had no specific relations to their hardness and strength. Adhesion of free Si was a main factor to determine a wear resistance of the Si/SiC composite. In the case of the Si/SiC/graphite, solid lubricationl and liquid reservoir of the graphite particles played the main role of the reduction of the friction force. In the torque test to estimate the possibility of practical of practical applications, the value of torque between the Al2O3 disk and Si/SiC/graphite disk was 1/6 lower compared with two $Al_2O_3$ disks on the basis of 100,000 cycles.

• 한국세라믹학회지
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• 제35권7호
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• pp.721-725
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• 1998

본 연구에서는 Boron과 Carbon black이 소결조재로 첨가된 탄화규소 분말을 $1950^{\circ}C$에서 상압소결 방법으로 시편을 제조하고 꺽임강도, 파괴인성, 비마모량을 측정하고 파단면 및 마찰마모면의 미세구조를 SEM으로 관찰하여 마찰마모특성과 미세구조와의 관계를 규명하였다. 또한 마모상대재료로서 SiC pin과 $Al_{2}O_{3}$ pin을 사용하였을때 마찰마모특성과 미세구조와의 관계도 비교 검토하였으며 다음과 같은 결론을 얻었다. 1. SiC pin을 사용한 경우 소결시편의 비마모량은 $Al_{2}O_{3}$ pin을 사용한 경우보다 많았으나, 가압하중이 증가하면 $Al_{2}O_{3}$ pin을 사용한 경우가 SiC pin을 사용한 경우보다 비마모량의 증가율이 6.5배로 되었다. 2. Pin의 비마모량은 SiC pin의 경우가 $Al_{2}O_{3}$의 경우보다 많았으나 가압하중이 증가하면 $Al_{2}O_{3}$ pin의 경우가 SiC pin의 경우보다 비마모향의 증가율이 약4배로 되었다. 3. 마모상대재료의 마찰계수가 작은 경우에는 마모면의 미세구조가 평활하면서 crack이 나타나지 않았으나, 마찰계수가 큰 경우에는 마모면이 평활치 못하고 crack의 전파현상이 크게 나타났다. 4. 사용된 Pin의 마찰계수가 큰 경우에는 고상소결한 SiC 시편도 액상소결한 시편과 마찰마모 특성이 유사하였다.

• 한국표면공학회지
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• 제47권5호
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• pp.263-268
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• 2014

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, $2.2{\mu}m$ thick NCD films were deposited on sintered 3 mm diameter SiC balls at $600^{\circ}C$ in a 2.45 GHz microwave plasma CVD system. Bare $ZrO_2$ and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against $ZrO_2$, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, $ZrO_2$ and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

• 대한기계학회논문집A
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• 제32권11호
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• pp.1003-1009
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• 2008

In this study, liquid phase sintered SiC (LPS-SiC) materials were made by hot pressing method. The particle size of nano-SiC powder was 30nm. Alumina ($Al_2O_3$), yttria ($Y_2O_3$) and silica ($SiO_2$) were used for sintering additives. To investigate effects of $SiO_2$, ratios of $SiO_2$ contents were changed by five kinds. Materials have been sintered for 1 hour at $1760^{\circ}C$, $1780^{\circ}C$ and $1800^{\circ}C$ under the pressure of 20MPa. The system of sintering additives which affects a property of sintering as well as the influence depending on compositions of sintering additives were investigated by measurement of density, mechanical properties such as flexural strength, vickers hardness and sliding wear resistance were investigated to make sure of the optimum condition which is about matrix of $SiC_f$/SiC composites. The abrasion test condition apply to load of 20N at 100RPM for 20min. Sintered density, flexural strength of fabricated LPS-SiC increased with increasing the sintering temperature. And in case of LPS-SiC with low $SiO_2$, sliding wear resistance has very excellent. Monolithic SiC $1800^{\circ}C$ sintering temperatures and 3wt% have excellent wear resistance.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.177-178
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• 2006

The results of monotonic and cyclic uniaxial compression tests, in which the deviatoric component of the stress is predominant, carried out on green and recrystallized iron compacts with different levels of density are presented and discussed in order to analyse the macro and micro-mechanisms governing the mechanical behaviour of non-sintered PM materials. The plastic deformation of the particles, especially at the contact areas between neighbouring grains, produces an internal friction responsible for the main features observed in the behaviour of green metallic compacts. These results show important discrepancies with the plasticity models, Cam-Clay and Drucker-Prager Cap.