Sliding Friction and Wear Behavior of GCr15 Bearing Steel at Different Temperatures

The effects of temperature on the friction and wear properties of GCr15 were studied by using a RETC multifunctional friction and wear testing machine. The microstructure characterization of the worn surface of the experimental steel was studied by means of metallographic microscope (OM), white light interferometer, secondary electron image (SEI) and back scattered electron image (BEI).The results show that the wear resistance of GCr15 bearing steel at room temperature is better than that at 100°C, 150°C and 200°C. At room temperature, the main wear forms of GCr15 are adhesion wear and fatigue wear. However, at 100°C, 150°C, 200°C, the friction coefficient and oxidation degree in the wear zone first increase and then decrease with the increase of temperature, and the wear form is mainly oxidized wear, accompanied by abrasive wear.

The Role of Transfer Layer on the Sliding Wear Behavior of a Cu-15Ni-8Sn Alloy Under Different Loads

We studied the microstructure of the transfer layer and its effect on the wear mechanism and wear property of an aged Cu-15Ni-8Sn alloy against GCr15 bearing steel during dry sliding by changing the applied load. The results indicate that the aged Cu-15Ni-8Sn alloy shows different wear behavior and wear properties when the applied load changed, where the average friction coefficient and specific wear rate decrease quickly with increasing applied load in steady wear condition. The sample tested under relatively high applied load shows the best wear performance owing the thickest oxide layer exists in the transfer layer. The main wear mechanisms were found changing with varied applied. The metallic nanocrystalline particles and the relative ductile copper oxides promotes the formation of a thick and densified oxide layer. The change of the thickness and morphology of the oxide layer under different load can significantly affect the wear mechanisms.

A New Approach to Calculate the Velocity of Interdendritic Fluid Flow during Solidification Using Etched Surface Height of Actual Metal Ingot

Macrosegregation remains one of main defects affecting metal materials properties, which is mainly caused by interdendritic fluid flow during solidifying. However, as for controlling actual specific segregation, it is still difficult to effectively measure or simulate this kind flow instead of pure fluid flow, especially in complex casting processes of high-grade materials. Herein, a new method for obtaining velocity magnitude and direction of interdendritic fluid flow during metal solidifying is proposed from boundary layer and standard deviation obtained by measuring etched surface heights of the actual ingot and using statistical principles. Taking continuous casting bloom of GCr15 bearing steel as an example, it is indicated that the calculated velocity magnitudes under different sides and superheats can be explained by process features and, hence, solidification mechanism. The velocity magnitude and fluctuation are higher on the inner curve side and under low superheat. Meanwhile, it is found that the fluctuation extent of secondary arm spacing is more relevant with interdendritic fluid flow, although its magnitude is mainly determined by the cooling rate. Moreover, on the basis of the calculated velocity directions and magnitudes, there is a positive correlation between segregation area ratio and the effective ratio between interdendritic flow velocity and growth velocity especially in the equiaxed grain zone, which corresponds with classic macrosegregation formation theory. The above findings and comparison with other results demonstrate the validity of the new approach, which can obtain the magnitude and the direction of interdendritic fluid velocity for two or three-dimensional multiscale velocity distribution by tailoring measuring length and numbers.