Polymer surfaces

Polymer Surfaces B. W. Cherry This book, which forms part of the Cambridge Solid State Science Series, consists of seven chapters. The first, "Polymer Surfaces", introduces the concept of surface energy and methods for its measurement and calculation. The second, "The SolidLiquid Interface", deals with surface tension, wetting and contact angles. Then follow chapters entitled "Adhesion and Adhesives", "Fracture of Polymers" and "Fracture Surface Energy and Strength". The final two chapters, "Friction and Adhesion" and "Deformation and Friction", a r e likely to be of more interest to tribologists. These last two chapters generally follow the classical Bowden and Tabor approach to the subject. Thus there is a rather lengthy section on the adhesion theory of friction and the deviations from Amontons' Laws exhibited by polymers. For elastomers, the activated rate process theory of friction, hysteresis and rolling friction, and Schallamach waves are described in some detail. The friction of plastics materials is dealt with more briefly. A separate section describes the low friction properties of ptfe and linear polyethylene, but it is not pointed out that very low speed/high load conditions are necessary before a coefficient of friction as low as 0.02 is obtained. The section on wear is rather cursory and only abrasive and fatigue wear are described. Curiously, I could find no reference to adhesive wear, and during my search I discovered an error in the index: the wrong page numbers were given for the subjects listed under "wear". The subjects are treated in a highly academic way through series of equations, and one is left with the impression that at least some of the equations are derived for their own sake rather than because they may shed more light on the topic. Consequently the book is more likely Published by Cambridge University Press, PO Box 110. Cambridge CB2 3RL, UK. tlard copy 1SBN 0 521 23082 9, paperback ISBN 0 521 29792 3

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to be of use to an undergraduate studying polymer physics than to an engineer looking for a deeper understanding of the tribological properties' of rubbers and plastics. The hardback edition of this book retails at £14.00 which seems expen-

sive for only 160 pages, but the paperback version is better value at £6.95.

D.C. Evans, Materials Research Department, Glacier Metal Company Ltd, Alperton, Wembley, Middlesex HAO 1HD, UK

Treatise on Materials Science and Technology - Volume 18

Ion Implantation Edited by J.K. Hirvonen The use of energetic ion beams to inject impurity atoms into the surface region of a solid offers the possibility of modifying the properties at the surface in a controllable manner. This is a relatively new technique, dating from the early 1970's. It has been used extensively to introduce dopants into semi-conductors, giving much better controllability and reproducibility for device fabrication as compared to thermal diffusion methods. More recently, ion implantation has been used to modify the mechanical and chemical properties of surfaces. This book concentrates almost exclusively on non-electronic aspects, and to the best knowledge of the writer is the first book to do so. Each chapter is written by a specialist contributor, resulting in a very high standard. In an introductory chapter, Hirvonen briefly describes the characteristics of ion implantation together with its advantages and disadvantages as a means of modifying surface properties. He also describes ion implantation equipment suitable for treating metal components on a production basis, and two potential applications of interest to the tribologist: the surface hardening of beryllium gas bearings and the improve. ment in corrosion resistance of steel bearings used in turbojet engines. Of greatest interest to the tribologist, however, is the chapter by N.E.W. Hartley "Tribological and Mechanical Properties". This contains a brief but adequate review of friction and wear mechanisms, and presents the results Published, price £37.80 ($55.00). by Academic Press lnc (London) Ltd, 24-28 Oval Road, London NWI 7DX, UK. ISBN 0 12341818 6

TRIBOLOGY international June 1981

of friction and wear experiments on a range of implanted surfaces. A variety of ions were implanted in En 352 steel and most caused a reduction in the coefficient of friction. However, lead implantation caused an increase. Wear tests on implanted surfaces indicated that in most cases a significant reduction in wear was achieved. Hartley discusses the basic mechanisms involved in the friction and wear of implanted surfaces, but the arguments are not totally convincing. Ion implantation can produce many effects, and it appears that further work is needed before these are fully understood. However, this is not a criticism of an excellent review chapter, but more an indication of the present state of the art. One fascinating result is that ion implantation can continue to give reduced wear rates when the surface has been worn away to a much greater depth than the original implanted layer, implying that the implanted species are mobile. Although many results are not fully understood, they are sufficiently promising to warrant commercial exploitation, and implantation equipment and results produced on a range of practical materials and components are reported, the most promising current practical applications being the hardening of dies and moulds. Also of direct interest to the tribologist is the chapter "Thermal Oxidation" by G. Dearnaley. This presents a very clear exposition of many examples of the beneficial effects of ion implantation on oxidation behaviour. For example, small doses of rare earth ions improve the adhesion of the oxide formed on stainless steel, and again the ions are trans-