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1996 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Tribology and Mechanics of Magnetic Storage Devices

verfasst von: Bharat Bhushan, Ph.D., D.Sc., P.E.

Verlag: Springer New York

Enthalten in: Professional Book Archive

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Über dieses Buch

Since January 1990, when the first edition ofthis first-of-a-kind book appeared, there has been much experimental and theoretical progress in the multi­ disciplinary subject of tribology and mechanics of magnetic storage devices. The subject has matured into a rigorous discipline, and many university tribology and mechanics courses now routinely contain material on magnetic storage devices. The major growth in the subject has been on the micro- and nanoscale aspects of tribology and mechanics. Today, most large magnetic storage industries use atomic force microscopes to image the magnetic storage components. Many companies use variations of AFMs such as friction force microscopes (FFMs) for frictional studies. These instruments have also been used for studying scratch, wear, and indentation. These studies are valuable in the fundamental understanding of interfacial phenomena. In the second edition, I have added a new chapter, Chapter 11, on micro­ and nanoscale aspects of tribology and mechanics of magnetic storage compo­ nents. This chapter presents the state of the art of the micro/nanotribology and micro/nanomechanics of magnetic storage components. In addition, typographical errors in Chapters 1 to 10 and the appendixes have been corrected. These additions update this book and make it more valuable to researchers of the subject. I am grateful to many colleagues and particularly to my students, whose work is reported in Chapter 11. I thank my wife, Sudha, who has been forbearing during the progress of the research reported in this chapter.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
The word tribology was first reported in a landmark report by Jost (1966). The word is derived from the Greek word tribos meaning rubbing, so the literal translation would be “the science of rubbing.” Its popular English language equivalent is friction and wear or lubrication science, alternatively used. The latter term is hardly all-inclusive; a leading American journal in the field categorizes its subjects of interest in the following technical areas: concentrated contacts; bearing materials, traction; friction and wear; fluid film bearings; lubricants; and wear control and seals. Dictionaries define tribology as the science and technology of interacting surfaces in relative motion and of related subjects and practices.
Bharat Bhushan
Chapter 2. Solid Surface Characterization
Abstract
The solid surface, or more exactly the solid-gas or solid-liquid interface, has a complex structure and complex properties dependent upon the nature of solids, the method of surface preparation, and the interaction between the surface and the environment. Properties of solid surfaces are crucial to surface interaction because surface properties affect real areas of contact, friction, wear, and lubrication (Bhushan et al., 1985; Bhushan, 1985). In addition to tribological functions, surface properties are important in other applications, such as electrical and thermal performance, painting, and appearance.
Bharat Bhushan
Chapter 3. Contact between Solid Surfaces
Abstract
For particulate magnetic media that have a polymeric binder, tribological behavior of the head-medium interface is affected by the physical properties of the polymers. Therefore, it is important to obtain a grasp of the physical properties of polymers.
Bharat Bhushan
Chapter 4. Friction
Abstract
Friction is the resistance to motion that is experienced whenever one solid body slides over another. The resistive force F, which is parallel to the direction of motion, is called the friction force [Fig. 4.1(a)]. If the solid bodies are loaded together and a tangential force (F) is applied, then the value of the tangential force that is required to initiate sliding is the static friction force. It may take a few milliseconds before sliding is initiated at the interface (F static). The tangential force required to maintain sliding is the kinetic (or dynamic) friction force (Fkinetic); it is sometimes also called drag force. Kinetic friction is either lower than or equal to the static friction [Fig. 4.1(b)].
Bharat Bhushan
Chapter 5. Interface Temperature of Sliding Surfaces
Abstract
The majority of surface effects are temperature dependent. This is not surprising because on an atomic scale mechanical, chemical, and electrical phenomena are generally dependent on the thermal energy available to assist or activate these phenomena. The mechanical properties (such as elastic modulus) and lubricating properties of many magnetic media start to degrade just above the ambient temperature. This degradation affects their tribological performance (Chapters 3 and 4). Therefore, an estimate of the interface temperature rise is necessary for the design of the head-medium interface (HMI).
Bharat Bhushan
Chapter 6. Wear Mechanisms
Abstract
Wear is the removal of material from one or both of two solid surfaces in a solid-state contact. It occurs when solid surfaces are in a sliding, rolling, or impact motion relative to one another. Wear occurs through surface interactions at asperities, and components may need replacement after a relatively small amount of material has been removed or if the surface is unduly roughened. In well-designed tribological systems, the removal of material is usually a very slow process but it is very steady and continuous. The generation and circulation of wear debris, particularly in machine applications where the clearances are small relative to the wear particle size, may be more of a problem than the actual amount of wear.
Bharat Bhushan
Chapter 7. Measurement Techniques of Head and Medium Wear
Abstract
The wear rate of modern heads is on the order of 100 nm per million meters of tape in the start-stop mode; the wear rate is about half in the streaming mode of operation. The life expectancy of a head is 3000 to 4000 hours equivalent to about 3 years of use with less than 1% failure rate (Bhushan, 1985). This wear rate is extremely small and difficult to measure. Consequently, there is a need for an accelerated test for determining the relative abrasivity of tapes (i.e., head wear resulting from abrasivity of different tapes) and resistance to wear of various head materials and head contours. Any change in the head contour affects its flying characteristics.
Bharat Bhushan
Chapter 8. Lubrication Mechanisms and Lubricants
Abstract
Sliding between clean solid surfaces is generally characterized by a high coefficient of friction and severe wear due to the specific properties of the surfaces, such as low hardness, high surface energy, reactivity, and mutual solubility. Clean surfaces readily adsorb traces of foreign substances, such as organic compounds, from the environment. The newly formed surfaces generally have a much lower coefficient of friction and wear than the clean surface. The presence of a layer of foreign material at an interface cannot be guaranteed during a sliding process; therefore, lubricants are deliberately applied to produce low friction and wear. The term lubrication is applied to two different situations: solid lubrication and fluid (liquid or gaseous) lubrication.
Bharat Bhushan
Chapter 9. Analysis and Measurement of Hydrodynamic Air Films
Abstract
In order to avoid wear, the head-medium interface (HMI) is designed so that the magnetic head is separated from the media by a thin air film (Chapter 1). The air film on which the head flies must be thick enough to prevent excessive material interactions under all operating conditions; yet, it must bе thin enough to give a sufficiently large recording signal. After startup, a full air bearing is developed above a certain sliding speed (known as takeoff speed). The air-film thickness profile is formed such that the resulting hydrodynamic air pressure balances the external loads applied at the interface. Intuitively, we can understand how it works by considering the boundary layer of the air that moves with the sliding surface. This layer gets compressed in the converging channel (present in all head-medium interfaces) of the air bearing so the hydrodynamic pressure develops and supports the load on an air cushion.
Bharat Bhushan
Chapter 10. Surface Finishing of Ceramic Head Materials
Abstract
Typical head body materials for tape and disk drives are Ni-Zn ferrite, Mn-Zn ferrite, aluminum oxide-titanium carbide (70% Al2O3, 30% TiC), yttria-stabilized zirconia/alumina-titanium carbide composite, calcium titanate (CaTiO3), or Foroceram (a ceramized, photosensitive glass). (For more details, see Chapter 1.) These materials are produced by hot isostatic pressing to give high-density and excellent mechanical properties. These materials are selected for their excellent wear resistance. Ferrites are ferromagnetic materials and are most widely used for many tape and disk heads. Ferrites have a spinal structure and both single-crystal and polycrystalline structures are used in hot pressed forms. Al2O3-TiC and calcium titanate are used for composite disk heads. Al2O3-TiC is the material most commonly used for thin-film disk heads. Yttria-stabilized zirconia and aluminum oxide-titanium dioxide coatings (plasma sprayed) are also used on the air-bearing surfaces of some composite tape heads for desired wear resistance.
Bharat Bhushan
Chapter 11. Micro/Nanotribology and Micro/Nanomechanics
Abstract
The micro/nanotribological and micro/nanomechanics studies are needed to develop fundamental understanding of interfacial phenomena on a small scale, and to study interfacial phenomena in micro- and nanostructures used in magnetic storage systems, microelectromechanical systems (MEMS), and other industrial applications (Bhushan, 1995a, 1995b, 1995c; Bhushan et al., 1995e, 1995f). Atomic force microscopes/friction force microscopes (AFMs/ FFMs) are used for these studies. In this chapter, we first present origins and significance of micro/nanotribology. Next we describe the AFM/FFM used for study of engineering surfaces in dry and lubricated conditions. Finally, we present examples of micro/nanotribological studies to conduct surface roughness, friction, adhesion, scratching, wear, indentation, detection of material transfer and lubrication studies, and the use of AFMs for nanofabrication/ nanomachining purposes.
Bharat Bhushan
Backmatter
Metadaten
Titel
Tribology and Mechanics of Magnetic Storage Devices
verfasst von
Bharat Bhushan, Ph.D., D.Sc., P.E.
Copyright-Jahr
1996
Verlag
Springer New York
Electronic ISBN
978-1-4612-2364-1
Print ISBN
978-1-4612-7517-6
DOI
https://doi.org/10.1007/978-1-4612-2364-1