Pyung Hwang

Anisotropic tribological properties of the coating on a magnetic recording disk

Mechanical and analytical tools were used to characterize the coatings on a magnetic recording disk. The mechanical and tribological properties of the coating were evaluated using the nano-indentation and nano-scratch tests. The transmission electron microscopy (TEM) and the Auger electron spectroscopy (AES) were used to determine the thickness and elemental compositions of the coating layers, while the atomic force microscopy (AFM) was used to study the surface topology and roughness. It was shown that the disk surface had a texture preferentially oriented along the circumferential direction with fairly uniform summit height and little waviness. The variations of surface roughness data were analyzed statistically, based on the Gaussian probability and Weibull cumulative probability theories. The coefficient of friction and the surface roughness were found to depend on scan direction relative to the coating texture. The hardness and elastic modulus were strongly influenced by the coating/substrate interaction and the surface roughness of the coating.

Hardness of bi-layer films on a leadframe substrate

The indentation hardness and elastic modulus of leadframe materials that consist of Cu alloy substrate and Ni/Pd bi-layer films of differing thicknesses are characterised using the micro-hardness and nano-indentation tests. The ‘true’ hardness of the individual substrate and film layers is evaluated based on the empirical relationship between the measured ‘composite’ hardness and the volume of plastically deformed material of film layers. It is found that the composite hardness determined from the nano-indentation test increases rapidly toward a peak at extremely low indentation depth of less than about 20–30 μm for all materials studied, due mainly to the finite value of the indenter tip radius and the rough surface of the specimen on the nano-scale. The composite hardness for the coated specimens decreases with further increasing indentation depth toward the hardness value of the substrate, because of the strong influence of the film/substrate interaction and the indentation size effect. The nano-indentation test in general gives higher true hardness values than those obtained from the micro-hardness test. Nevertheless, the relative hardness values of the substrate and films determined from the two tests are consistent. The hardness of Ni film is about 20 to 50% greater than that of Cu alloy, whereas the hardness of Pd film is 7 to 11 times the Ni film in the nano-indentation test.

Effectiveness of multi-shape laser surface texturing in the reduction of friction under lubrication regime

Purpose – The purpose of this paper is to investigate and discuss the effect of multi-shape laser surface texturing (LST) steel surfaces on tribological performance. Design/methodology/approach – The textured surface with some specific formula arrays was fabricated by laser ablation process by combining patterns of circles and triangles, circles and squares and circles and ellipses. The tribological test was performed by a flat-on-flat tribometer under dry and lubrication conditions, and results were compared with that of untextured surface. Findings – The results showed that the textured surface had better friction coefficient performance than the untextured surface due to hydrodynamic lubrication effect. Through an increase in sliding speed, the beneficial effect of LST performance was achieved under dry and lubrication conditions. Originality/value – This paper develops multi-shape LST steel surfaces for improving the friction and wear performance under dry and lubrication conditions.

Bifurcation Analysis of the Load/Unload Systems With Multiple Flying Height States

The load/unload behavior of the hard disk drive slider is studied in terms of the air bearing static characteristics. The application of numerical continuation methods to calculate spacing diagrams is proposed. The algorithm that detects multiple flying height states and fold points is developed. The relationship between suspension force x-offset and critical preload is found for femto size sliders. The second fold corresponding to the critical preload for unloading is found in the negative air bearing force area. The range of x-offsets and preloads where bi-stable phenomenon exists is depicted on the stability diagram. The perturbation method is used to check the dynamic system characteristic values near the fold points and to determine the stability of the solution branches. The present procedure can be employed to study the multiple flying height states in the terms of any other pair of parameters besides the preload and x-offset.

Application of Optimization Approach to Static FE Analysis of Hard Disk Drive Slider

The objective of the present work is to present the numerical analysis of the computer hard disk slider. The air film pressure is calculated using the finite element method. The conjugate-gradient method and the perturbation method are employed in the static analysis of the slider. The steady state attitude of the femto slider is studied for various radial positions and skew angles. It is found that the perturbation method is an efficient method for gradient evaluation. Also, it is shown that optimization of the Hessian matrix form accelerates the search process.

EFFECT OF THE TEMPERATURE ON THE FRICTION AND WEAR PROPERTIES OF BULK AMORPHOUS ALLOY

The present paper report the results of an experimental investigation of the temperature effect on the sliding friction and wear properties of the bulk metallic glass (BMG). To improve the friction and wear properties of the BMG, the disk specimens were developed in the alloy system of Fe67.6C7.1Si3.3B5.5P8.7Cr2.3Mo2.6Al2Co1.0 using hot metal and industrial ferro-alloys. The friction and wear test was performed using flat-on-flat contact configuration of unidirectional tribometer and Si3N4 ceramic disk used as a counterpart. The worn surfaces of the BMG were observed by using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The results indicated that the friction and wear properties of the BMG depend on the glass transition and the formation of protective oxide film. The friction coefficient decreased with increasing temperature, while it increased slightly when the temperature passed the glass transition temperature (Tg). The worn specimens were exposed to abrasion, adhesion, oxidation and plastic deformation. In addition, obvious surface flow characteristics was accompany during wear test.

Non-Iterative Finite Element Scheme for Combined Annular-Thrust Porous Aerostatic Bearings Analysis

The key points of method derivation and a numerical example for bearing with three dimensional air flow are presented.Copyright

Indentation properties of copper leadframe with hard coatings

Hardness and elastic modulus of a typical leadframe material which consists of a Cu alloy substrate with Ni and Pd bi-layer coatings were characterised using Vicker’s micro-hardness and nano-indentation tests. The two different testing methods produced similar results in that ‘composite’ hardness for all coated specimens decreased (except at very low loads in the nano-indentation test) with increasing indentation depth and tended to converge at sufficiently high loads due to the strong influence of the coating/substrate interaction. The hardness values of substrate and Ni and Pd coatings were successfully determined from the ‘composite’ hardness values based on the empirical linear relationship with the inverse of indentation diagonal and the rule of mixtures principle.

Computational analysis on Hybrid Electric Motorcycle with front wheel electric motor using Lithium Ion battery

This paper presents a study related to Hybrid Electric Motorcycle (HEM) with a front wheel DC electric hub motor using Lithium Ion battery that renovated from Honda Lead 110cc. The rear wheel is driven by drive train integrated with a continuously variable transmission (CVT) as its origin. Both of them are able to provide propulsion torque separately or simultaneously. Fuel consumption and performance characteristics of the proposed design will be evaluated by a dynamic simulation model in Matlab/Simulink. The obtained results show that plug - in hybrid structure without generator is the most feasible and effective choice to renovate a traditional scooter in traffic condition of many populous cities in Vietnam. The study also illustrated fuel economy can save up to 21.1% with the same performance characteristics between the plug - in hybrid scooter and original one.

A comparative study of the friction and wear performance of Fe-based bulk metallic glass under different conditions

Purpose This study aims to compare the friction and wear behaviors of Fe68.3C6.9Si2.5 B6.7P8.8Cr2.2Al2.1Mo2.5 bulk metallic glass (BMG) under sliding using dry, deionized water-lubricated and oil-lubricated conditions. The comparison was performed using a unidirectional ball-on-flat tribometer under different applied loads, and the results were compared to the properties of a conventional material, SUJ2. Fe-based BMG materials have recently been attracting a great deal of attention for prospective engineering applications. Design/methodology/approach As a part of the development of Fe-based BMGs that can be cost-effectively produced in large quantities, an Fe-based BMG Fe68.8C7.0Si3.5B5.0P9.6 Cr2.1Mo2.0Al2.0 with high glass forming ability was fabricated. In the present study, the friction and wear properties of Fe-based BMG has been comparatively evaluated under dry sliding, deionized water- and oil-lubricated conditions using a unidirectional ball-on-flat tribometer under different applied loads, and the results were compared to the properties of conventional material SUJ2. Findings The results show that the Fe-based BMG had better friction performance than the conventional material. Both the friction coefficient and wear mass loss increased with increasing load. The sliding wear mechanism of the BMG changed with the sliding conditions. Under dry sliding conditions, the wear scar of the Fe-based BMG was characterized by abrasive wear, plastic deformation, micro-cracks and peeling-off wear. Under water- and oil-lubricated conditions, the wear scar was mainly characterized by abrasive wear and micro-cutting. Originality/value In this investigation, the authors developed a new BMG alloy Fe68.8C7.0Si3.5B5.0P9.6Cr2.1Mo2.0Al2.0 to improve the friction and wear performance under dry sliding, deionized water- and oil- lubricated conditions.