Young-Hun Chae

Tribological characteristics of silicon nitride at elevated temperatures

A sliding friction-and-wear test for silicon nitride (Si3N4) was conducted using a ball-on-disk specimen configuration. The material used in this study was HIPed silicon nitride. The tests were carried out from room temperature to 1000 °C using self-mated silicon nitride couples in laboratory air. The worn surfaces were observed by SEM and the debris particles from the worn surfaces were analyzed for oxidation by XPS. The normal load was found to have a more significant influence on the friction coefficient of the silicon nitride than an elevated temperature. The specific wear rate was found to decrease along with the sliding distance. The specific wear rate at 29.4 N and 1000 °C was 292 times larger than that at room temperature. The main wear mechanism from room temperature to 750 °C was caused by brittle fracture, whereas from 750 to 1000 °C the wear mechanism was mainly influenced by the oxidation of silicon nitride due to the increased temperature. The oxidation of silicon nitride at a high temperature was a significant factor in the wear increase.

WEAR MECHANISMS MAP PROPOSAL OF CRANE SHEAVE STEEL MATERIALS

In contact conditions of crane sheave steel materials against a wire rope the contact surface of the sheave generally metal wear. In this study. Alternating bending wear tests using the normalized low carbon cast steel were out under four kinds of applied loads, and rotation speeds at 28rpm. The wear characteristics, and wear mechanism map on the worn surfaces was examined. The results of this study indicate that the wear rate of the substrate depends on the diameter of the wire ropes. The wear mechanism of the substrate is characterized by fatigue wear, but it was the wear transition happened in number of contact cycle. The temperature variation of the substrate groove was measured at 52°C, in average. Also it has been affected the surface crack propagation occurs with a movement of hertz by thermal stress and a wear mechanisms map has been proposed.

Tribological performance of Al2O3/NiCr coating

The tribological performance of Al2O3/NiCr coating deposited on steel (SM45C) was investigated under lubrication. The parameters of sliding wear consist of normal load and coating thickness. Test result showed that there was no evidence of an improved bonding strength in the coating. However, the wear resistance of the Al2O3/NiCr coating was significantly greater than that of the Al2O3 coating. It was evident that the residual stress for the AI2O3 coating was higher than that of the Al2O3/NiCr coating from the scratch test failure of coating. The bond coating played an important role in decreasing the residual stress. Also, it was found that the residual stress had a notable influence on the wear mechanism.

Friction Characteristics for Density of Micro Dimples Using Photolithography

Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

SLIDING WEAR BEHAVIOR OF PLASMA SPRAYED ZIRCONIA CERAMIC COATING UNDER DIFFERENT CONDITIONS

The sliding wear behavior of ZrO2 -22wt%MgO (MZ) and ZrO2 -8wt%Y2 O3 (YZ) deposited on a cast aluminum alloy with bond layer (NiCrCoAlY) by plasma spray against a SiC ball was investigated under dry and lubrication conditions at room temperature. At all load conditions, the wear mechanisms of the MZ and YZ coatings were almost the same. The wear mechanism involved material transfer and pullout under dry condition, but micro-fractures and spallation under lubrication condition. When oil was used for lubrication, the friction coefficient of the sliding pairs and the wear loss of the ceramics were reduced. The wear loss of the MZ coating was less than that of the YZ coating under dry test, but more than that of the YZ coating under lubrication test. The test conditions and the mechanical properties of the ceramic coatings were correlated to the wear performance.Copyright

A Fundamental Study for the Sliding Wear Characteristics of the Crane Sheave Against a Rope Wire

The sliding wear characteristics of the crane sheave were investigated using a pin on disk rig tester. The experiment was conducted using a high carbon steel wire that was upper material, also carbon steel castings that was disk material. There are various operating conditions in this work. At the room temperature, we carried out the wear test under a grease lubrication and dry condition. The results of wear test showed that an annealed-casted have lower, also the wear curves are linearly increased with increasing of sliding distance. For the specific wear rate of annealed-casted, the wear resistance was increased with decreasing diameter of wire. The wear of a wire and a disk have a different mechanism, the one is the abrasive wear due to fatigue wear under lubrication, another is the adhesion wear under dry condition.

Sliding Wear Behavior of

The sliding wear behavior of coating deposited on steel(SM45C) was investigated under lubrication. The parameters of sliding wear are normal loads, coating thickness. As a result, the wear resistance of coating was remarkably greater than that of coating. The optimized coating thickness was found to be to ensure good anti-wear. The bond coating played important role in decreasing residual stress. The residual stress had much influence on wear mechanism. These results were correlated with the stress state of coating and the microstructure of coating.