Auezhan Amanov

Friction and Wear Characteristics of C/Si Bi-layer Coatings Deposited on Silicon Substrate by DC Magnetron Sputtering

The tribological behavior of carbon/silicon bi-layer coatings deposited on a silicon substrate by DC magnetron sputtering was assessed and compared to that of amorphous carbon and silicon coatings. The motivation was to develop a wear resistant coating for silicon using thin layers of amorphous carbon and silicon. Wear tests were conducted by sliding a stainless steel ball against the coating specimens under applied normal loads in the range of 20xa0~xa050xa0mN. Results showed that the wear rate of the bi-layer coating was strongly dependent on the ratio of thickness between the carbon and silicon layers. The wear rate of the bi-layer coating with 25xa0nm thick carbon and 102xa0nm thick silicon layers was about 48 and 20 times lower than that of the single-layer amorphous carbon and amorphous silicon coating, respectively. In addition, the steady-state friction coefficient of the bi-layer coating could be decreased to 0.09 by optimizing the thickness of the layer. Finally, a model for the wear reduction mechanism of the carbon/silicon bi-layer coating was proposed.

Wear Enhancement of Wheel-Rail Interaction by Ultrasonic Nanocrystalline Surface Modification Technique

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique was applied to normal and heat-treated rails made of 60 kgK steel to enhance the wear resistance of the wheel-rail interaction. The hardness and compressive residual stress values of the untreated and UNSM-treated rails were measured by the Brinell hardness tester and X-ray diffraction technique, respectively. It was found, according to the measurement results, that the hardness was increased by about 20% and 8%, whereas the compressive residual stress was induced by about 52% and 62% for the UNSM-treated normal and heat-treated rails, respectively. The UNSM-treated normal rail showed a slightly higher hardness than the heat-treated rail. The wear resistance of rails with respect to rotating speed and rolling time was assessed using a rolling contact wear (RCW) tester under dry conditions. The RCW test results revealed that the wear of the UNSM-treated rails was enhanced in comparison with those of the untreated rails. Also, the wear amount of the rails was increased with increasing the rotation speed. The UNSM-treated normal rail exhibited the highest wear resistance with respect to the rotation speed. The wear mechanisms of the rails are also discussed based on microscopic images of the worn out surfaces.

Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy

Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S2PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta.

Friction and Wear Reduction of Eccentric Journal Bearing Made of Sn-Based Babbitt for Ore Cone Crusher

An anti-friction Babbitt alloy-coated bearing made by a casting process is a journal bearing, which is used in an ore cone crusher eccentric. The main purpose of the Babbitt coated eccentric is to provide a low friction to support and guide a rotating shaft. Despite the fact that the Babbitt-coated eccentric offers a low friction coefficient and can be operated without a continuous supply of lubricant, it suffers from mining environments and short service life. In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique was used to further reduce the friction coefficient, to increase the wear resistance, and to extend the service life of the Sn-based Babbitt metal. The friction and wear behavior of the Sn-based Babbitt metal was investigated using a block-on-ring tester under both dry and oil-lubricated conditions. The results of the experiments revealed that the friction and wear behavior of Sn-based Babbitt metal could be improved by the application of the UNSM technique. The friction and wear mechanisms of the specimens were explained and discussed in terms of changes in surface properties—microstructure, surface hardness, surface roughness, etc.

Increase in Strength and Fretting Resistance of Alloy 718 Using the Surface Modification Process

This work comparatively investigated the strength (hardness, yield strength, dynamic elastic modulus, and surface residual stress), fretting failure, and corrosion resistance of the as-received and treated Ni-based superalloy Alloy 718. The goal of the current research is to improve the hardness, fretting wear, and corrosion resistances of Alloy 718 through the ultrasonic nanocrystal surface modification (UNSM) process with the aim of extending the lifespan of aircraft and nuclear components made of Alloy 718. The experimental results revealed that the surface hardness increased by about 32%, the fretting wear resistance increased by about 14%, and the corrosion resistance increased by about 18% after UNSM process. In addition, the UNSM process induced a tremendous high compressive surface residual stress of about −1324 MPa that led to an increase in yield strength and dynamic Young’s modulus by about 14 and 9%, respectively. Grain size refinement up to ~50 nm after the UNSM process is found to be responsible for the increase in surface hardness as well. The depth of the effective layer generated by the UNSM process was about 20 µm. It was concluded that the UNSM process played a vital role in increasing the strength and enhancing the corrosion and fretting resistances of Alloy 718.

Bearings Downsizing by Strength Enhancement and Service Life Extension

Slim bearings are used widely in aircrafts, robots, wind turbines, and industrial machineries, where their size and weight are very important for the performance of a system. The common materials of slim bearings for robots and industrial machineries are based on SAE52110 bearing steel, and special heat treatment and a super polishing process are used and adapted to improve the rolling contact fatigue (RCF) strength of bearings. The improvement in RCF strength, depending on contact stress, surface hardness, and the friction behavior before and after ultrasonic nanocrystalline surface modification (UNSM) treatment was validated. Simple analysis shows that these improvements can reduce the size and weight of slim bearings down to about 3.40–21.25% and 14.3–26.05%, respectively. Hence, this UNSM technology is an opportunity to implement cost-saving and energy consuming super-polishing, a heat treatment process, and to reduce the size and weight of slim bearings.