Introduction to Surface Engineering and Functionally Engineered Materials

Scrivener Publishing

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Salem, MA 01970

Scrivener Publishing Collections Editors

James E. R. Couper | Ken Dragoon
Richard Erdlac | Rafiq Islam
Pradip Khaladkar | Vitthal Kulkarni
Norman Lieberman | Peter Martin
W. Kent Muhlbauer | Andrew Y. C. Nee
S. A. Sherif | James G. Speight

Publishers at Scrivener

Martin Scrivener (martin@scrivenerpublishing.com)

Phillip Carmical (pcarmical@scrivenerpublishing.com)

Copyright © 2011 by Scrivener Publishing LLC. All rights reserved.

Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

ISBN 978-0-470-63927-6

To Ludmila, Katherine and Erin

Preface

Surface engineering has become an indispensible technology for improving virtually all the properties of solid surfaces. Almost all types of materials, including metals, ceramics, polymers, and composites can be coated with thin films or surface structures of similar or dissimilar materials. It is also possible to form coatings of newer materials (e.g., met glass. beta-C3N4), graded deposits, nanocomposites, and multi-component deposits etc. Functional surface engineering has provided advancements such as extending the life of optoelectronic devices, cutting tools, engine parts, medical implants, hardware and plumbing fixtures; improved corrosion resistance of ferrous materials; wear resistant decorative coatings for jewelry and architectural glass; improved reflectivity and hardening of laser and telescope mirrors, improved efficiency and manufacturing of photovoltaic cells; new energy efficiency glazings (low-e windows); thin film batteries; self cleaning surfaces and much more.

Surface engineering can be traced back as far as the mid-1900’s to first efforts to modify the properties of solid surfaces to reduce wear, reduce friction and improve appearance. In the second half of the last century, however, surface engineering involved primarily application of thin film materials and plasma treatment to modify and enhance surface properties such as wear resistance, lubricity and corrosion resistance. It has evolved to cover the full range of surface properties, such as optical, electrical, magnetic, electro-optical properties, permeation barriers, and functionally engineered materials. Each of these properties can be subdivided into dozens of subtopics. It has further evolved to encompass artificial structures and surfaces such as low dimensional structures (super-lattices, quantum wires and quantum dots), nanotubes, sculpted thin films, nanocomposites, energy band engineering, and even biological structures. A number of technical conferences are solely or partially dedicated to surface engineering and functional materials engineering. Excellent resources are the Society of Vacuum Coaters (SVC), AVS and Materials Research Society (MRS) and their associated publications.

The scope of this book is an introduction to a wide variety of aspects of surface engineering and functional materials engineering. There are a number of excellent books on the market that cover the topics such as hard coatings, deposition technologies for thin films, physical vapor deposition, nanocomposites, and low dimensional materials. No one book, however, incorporates all aspects of surface engineering and engineered materials. To this end, this book is intended to present a wide variety of surface engineering and functional materials engineering aspects in less detail than specialized handbooks, but as a standalone resource.

This book is intended to serve as an introduction to a multitude of surface engineering and functional materials engineering topics and should viewed as such. In most cases, only the basics are addressed. Because of this, thin films with more than three components have generally been omitted. Advanced engineered materials such as carbon and titania nanotubes, nanocomposites, metamaterials, sculpted thin film, photonic crystals and low dimensional structures show promise of enhanced structural, optical and electrical properties. Only basic mechanical, optical and electrical properties are presented. As much math as logically possible has been omitted without damaging basic concepts. It was unavoidable, however, to go into more detail with regard to thin film nucleation, energy band engineering and nanoelectronics.

Engineered materials are now being developed for and used in advanced photovoltaic devices, dye sensitized solar cells, quantum cascade lasers, advanced electronics, drug delivery, medical devices, metamaterials, optical photonic bandgap devices, negative refractive index devices, superlenses, artificial magnetism, cloaking devices, thermoelectric power generation and much more. Structures and properties not possible in naturally occurring materials are synthesized by a number of lithographic, etching, plasma and deposition processes.

The structure and properties of thin films are almost entirely dependent on deposition process. Many properties are directly related to the energy of atoms and molecules incident on the substrate surface. It is essential to understand how each deposition process synthesizes thin film structure and composition and the adatom energetic of each process. To this end, a significant amount of text, namely chapters 2 and 3, is dedicated to deposition processes and structure of thin films. In the ensuing chapters, it will become evident how the properties of each type of thin film (tribological, optical, electrical, etc.) depend on deposition conditions, structure and bonding. Tables are presented in each chapter that summarize these relationships. It was impossible to survey all literature on each deposition process and thin film material, and as a result, many tables are incomplete due to lack of available information.

The surveys of low dimensional structures, metamaterials and nanotubes may seem out of place but these technologies are being increasingly used to improve the tribological, optical, electrical and optoelectronic performance of thin film structures and surface devices. Sculpted thin films synthesized by glancing angle deposition (GLAD) are now used to achieve properties not possible with conventional thin film materials. Metamaterials are one of the most significant technical developments of this decade and are being developed with optical properties (e.g., negative refractive index) not possible with solid thin films. Applications include cloaking devices and superlenses than can resolve below the diffraction limit.

It is hoped that this book will give the readers enough background information to begin to solve critical surface engineering and materials problems, or provide enough information and resources to spring board them to generate new solutions and materials.

Peter M. Martin
June, 2011
Kennewick, WA

Chapter 1

Properties of Solid Surfaces

1.1 Introduction

Wear and corrosion of structural materials are ubiquitous reliability and lifetime problems that have existed since the inception of mechanical devices and structures. Additionally, the optical, electrical, and electro-optical properties of solid surfaces were determined by crystalline, compositional, and electrical properties of the bulk solid. Until the advent of surface engineering, these properties belonged to the surface of the bulk materials being used and could be modified to only a limited degree by various metallurgical and plasma surface treatments. Surfaces of bulk materials could be hardened and wear corrosion resistance increased by a number of external treatments, including plasma bombardment, ion implantation, anodization, heat treatment, plasma nitriding, carburizing and boronizing, pack cementation, and ion implantation. They could also be polished or etched to modify optical properties and electrical properties to a limited degree.

Surface Engineering provides additional functionality to solid surfaces, involves structures and compositions not found naturally in solids, is used to modify the surface properties of solids, and involves application of thin film coatings, surface functionalization and activation, and plasma treatment. It can also be defined as the design and modification of the surface and substrate of an engineering material together as a system, to give cost effective performance of which neither is capable alone.

Surface engineering techniques are being used in the automotive, aerospace, missile, power, electronic, biomedical, textile, petroleum, petrochemical, chemical, steel, power, cement, machine tools, and construction industries. Surface engineering techniques can be used to develop a wide range of functional properties, including physical, chemical, electrical, electronic, magnetic, mechanical, wear-resistant and corrosion-resistant properties at the required substrate surfaces. Almost all types of materials, including metals, ceramics, polymers, and composites can be coated on similar or dissimilar materials. It is also possible to form coatings of newer materials (e.g., met glass. b-C3N4), graded deposits, multi-component deposits, etc.

In 1995, surface engineering was a £10 billion market in the United Kingdom. Coatings, to make surface life resistant to wear and corrosion, was approximately half the market.

In recent years, there has been a paradigm shift in surface engineering from age-old electroplating to processes such as vapor phase deposition, diffusion, thermal spray and welding using advanced heat sources like plasma, laser, ion, electron, microwave, solar beams, pulsed arc, pulsed combustion, spark, friction and induction. Biological materials for self-healing, self-cleaning and artificial photosynthesis are now becoming involved.

It is estimated that loss due to wear and corrosion in the U.S. is approximately $500 billion. In the U.S., there are around 9524 establishments (including automotive, aircraft, power, and construction industries) who depend on engineered surfaces with support from 23,466 industries.

There are around 65 academic institutions world-wide engaged in surface engineering research and education.

Surface engineering can be traced as far back as Thomas Edison in 1900 with the plating of gold films [1]. In 1938, Berghaus was among the first to develop plasma and ion modification of surfaces to improve surface properties and properties of vacuum deposited coatings [2]. The ion plating process, developed in the early 1960’s, was a significant step forward in plasma-assisted coating deposition [3, 4, 5]. Ion plating was the first true industrial surface engineering process. Because conventional dc-diode sputtering used for ion plating did not provide sufficient levels of ionization to permit deposition of dense ceramic coatings with adequate mechanical properties, post deposition processes such as peening were often required to density the coating. After the early 1970’s, the history of surface engineering is intimately connected to the development of thin film deposition and plasma processes and closely parallels the history of physical vapor deposition (PVD) coatings and processes (magnetron sputtering, ion assisted deposition), plasma processing, and chemical vapor deposition (CVD) processes in particular.

The majority of surface engineering technology has focused on enhancement of tribological properties (hardness, wear resistance, friction, elastic moduli) and corrosion resistance. The purist might think that surface engineering encompasses only tribological and wear resistant treatments, as initiated by Ron Bunshah as far back as 1961 [6]. Many engineering components need wear or corrosion resistant surfaces as well as tough, impact-resistant substrates. These requirements can be best met by using treatments that alter surface properties without significantly modifying those of the core, or bulk, material. If these principles are applied correctly, surface engineering brings many benefits, including:

Lower manufacturing costs

Reduced life cycle costs

Extended maintenance intervals

Enhanced recyclability of materials

Reduced environmental impact

There are, however, many more properties of a solid surface that can be enhanced by application of thin films, plasma treatment, patterning and nanoscale structures. This is reflected in the programs of a number of technical conferences dedicated solely to surface engineering (International Conference on Metallurgical Coatings and Thin Films, for example), starting as early as 1974 [6]. The first conferences focused on modification of the surface of a component to enhance its the overall performance. This area, however, has grown much broader than just this technology, as demonstrated by the symposia presented at the 2010 International Conference on Metallurgical Coatings and Thin Films (ICMCTF), sponsored by the Advanced Surface Engineering Division of AVS. Conference symposia include:

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