Preface

This book is about the selection of materials for applications in which interactions between rubbing surfaces or substances are a design concern. It is about the friction response of various materials under conditions that are likely in service, the wear and erosion of materials, and the testing to address friction wear and erosion (tribology) concerns. Its purpose is to review what is known about the tribology of important material systems and to show how to select appropriate materials from each family of engineering materials. The objective of the book is to learn how to design materials so that they do not fail because of tribological issues.

The terms friction, wear, erosion, and lubrication were merged into one term, tribology, in the 1960s when the Institution of Mechanical Engineers in the United Kingdom commissioned the Encyclopedia Britannica to create a word to describe the science of interacting surfaces. In this book, the prefix tribo is used. Tribology is a good word because any time surfaces rub, there are many possible interactions. Tribology includes the friction aspects, the lubrication aspects, and the damage aspects.

Countless studies have shown that the annual cost of friction and wear in developed countries ranges between 5 and 15% of the gross domestic product. Failures caused by using the wrong material are one aspect of the annual cost of friction and wear; short service life is another example (five years is often the life of an automobile), and energy losses due to friction are a huge contributor to global warming and to the annual cost of wear. Only one-third of the horsepower of an automobile engine is used in moving the vehicle on its intended path. The right material for a tribological application is important. Tribomaterials are important.

This book is written in traditional textbook style for use as a teaching text, but it can also serve as a reference for anyone who finds a friction, wear, or erosion concern to be a limiting factor in a design or in the operation of an existing machine or operation. The text in this book contains tribotesting data and tribology research that are the product of decades of work in the field by the authors, with the past 20 years in one of the United States’ best-equipped tribotesting laboratories.

This book contains many italicized statements similar to the preceding text. The reader should take note of these because they are intended as important points.

Laboratory tests that correlate with service and the results from these tests are presented in each chapter as selection aids.

Most of the test results used to compare the response of different materials to tribotests are historical data from papers presented by the authors at various conferences over the past 40 years or so. Some wear and friction studies were conducted at Bud Labs specifically for this book.

The book is organized with chapters on each of the important families of engineering materials that have utility in addressing tribology problems, such as copper alloys, cast irons, stainless steels, plastics, elastomers, ceramics, cermets, and coatings. A chapter is included on biotribology because it is an emerging part of engineering. There are many materials selection issues in biotribology because of corrosion and patient-reaction issues.

This book contains chapters on the types and mechanisms of friction, wear, and erosion, as well as a chapter on tribotesting. The latter illustrates how laboratory testing can supply needed selection information. The book concludes with a chapter on the tribology of lubricants and another on the materials selection process. The lubrication chapter is intended to introduce the subject to readers who are lubricant users rather than lubricant formulators. The last chapter presents methodology to quantify candidate properties by using a selection matrix.

Each chapter contains a chapter summary with a glossary, takeaway concepts, questions for discussion, references, and selected references.

The engineering units used are generally SI and English, in keeping with the style of Friction, Lubrication, and Wear Technology, Volume 18 of ASM Handbook, 2017. However, many of the historical graphs and tables are presented in the units used in the original studies; this was done to prevent possible conversion errors. In addition, small dimensions are given only in nanometers, micrometers, or millimeters, and small forces are in Newtons. This is because the authors feel these units are the most appropriate.

Tribology is a unique field. The interactions between rubbing surfaces can be very complicated and unpredictable. However, laboratory testing and industrial experiences have shown that most engineering materials have niches in which they perform well. This book is an attempt to share this accumulated knowledge and, in doing so, to help readers produce designs without tribological issues.