Friction and wear are important when considering the operation and efficiency of components and mechanical systems. Among the different types and mechanisms of wear, adhesive wear is very serious. Adhesion results in a high coefficient of friction as well as in serious damage to the contacting surfaces. In extreme cases, it may lead to complete prevention of sliding; as such, adhesive wear represents one of the fundamental causes of failure for most metal sliding contacts, accounting for approximately 70% of typical component failures. This article discusses the mechanism and failure modes of adhesive wear including scoring, scuffing, seizure, and galling, and describes the processes involved in classic laboratory-type and standardized tests for the evaluation of adhesive wear. It includes information on standardized galling tests, twist compression, slider-on-flat-surface, load-scanning, and scratch tests. After a discussion on gear scuffing, information on the material-dependent adhesive wear and factors preventing adhesive wear is provided.

This article considers the main characteristics of wear mechanisms and how they can be identified. Some identification examples are reported, with the warning that this task can be difficult because of the presence of disturbing factors such as contaminants or possible additional damage of the worn products after the tribological process. Then, the article describes some examples of wear processes, considering possible transitions and/or interactions of the mechanism of fretting wear, rolling-sliding wear, abrasive wear, and solid-particle erosion wear. The role of tribological parameters on the material response is presented using the wear map concept, which is very useful and informative in several respects. The article concludes with guidelines for the selection of suitable surface treatments to avoid wear failures.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

Fretting is a wear phenomenon that occurs between two mating surfaces; initially, it is adhesive in nature, and vibration or small-amplitude oscillation is an essential causative factor. Fretting generates wear debris, which oxidizes, leading to a corrosion-like morphology. This article focuses on fretting wear related to debris formation and ejection. It reviews the general characteristics of fretting wear, with an emphasis on steel. The review covers fretting wear in mechanical components, various parameters that affect fretting; quantification of wear induced by fretting; and the experimental results, map approach, measurement, mechanism, and prevention of fretting wear. This review is followed by several examples of failures related to fretting wear.

Impact or percussive wear is defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another body. Impact wear, however, has many analogies to the field of erosive wear. The main difference is that, in impact wear situations, the bodies tend to be large and contact in a well-defined location in a controlled way, unlike erosion where the eroding particles are small and interact randomly with the target surface. This article describes some generic features and modes of impact wear of metals, ceramics, and polymers. It discusses the processes involved in testing and modeling of impact wear, and includes two case studies.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.

This article briefly introduces the concepts of failure analysis, including root-cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It initially provides definitions of failure on several different levels, followed by a discussion on the role of failure analysis and the appreciation of quality assurance and user expectations. Systematic analysis of equipment failures reveals physical root causes that fall into one of four fundamental categories: design, manufacturing/installation, service, and material, which are discussed in the following sections along with examples. The tools available for failure analysis are then covered. Further, the article describes the categories of mode of failure: distortion or undesired deformation, fracture, corrosion, and wear. It provides information on the processes involved in RCA and the charting methods that may be useful in RCA and ends with a description of various factors associated with failure prevention.

Rolling-contact fatigue (RCF) is a common failure mode in components subjected to rolling or rolling-sliding contact. This article provides a basic understanding of RCF and a broad overview of materials and manufacturing techniques commonly used in industry to improve component life. A brief discussion on coatings to improve surface-initiated fatigue and wear is included, due to the similarity to RCF and the increasing criticality of this failure mode. The article presents a working knowledge of Hertzian contact theory, describes the life prediction of rolling-element bearings, and provides information on physics and testing of rolling-contact fatigue. Processes commonly used to produce bearings for demanding applications are also covered.

Erosion of a solid surface can be brought about by liquid droplet impingement (LDI), which is defined as "progressive loss of original material from a solid surface due to continued exposure to erosion by liquid droplets." In this article, the emphasis is placed on the damage mechanism of LDI erosion under the influence of a liquid film and surface roughness and on the prediction of LDI erosion. The fundamentals of LDI and processes involved in initiation of erosion are also discussed.

Vibrothermography, also known as sonic thermography, sonic infrared (IR), thermosonics, and vibroacoustic thermography, is a nondestructive evaluation (NDE) technique for finding cracks and delaminations through vibration-induced heating. This article describes the four parts of the vibrothermography process: vibration of the specimen by a transducer; conversion of vibrational energy into heat by a crack, delamination, and other contacting surfaces; conduction of the heat to an external surface; and infrared detection of the heat with a thermal camera.

This article describes the nitriding methods of titanium alloys such as plasma nitriding and gas nitriding. It focuses on the interaction of titanium alloys, interaction of titanium with nitrogen, and the interaction of titanium with oxygen, carbon, and hydrogen. The article provides information on the wear and fatigue properties and corrosion resistance of nitrided titanium alloys, as well as the effect of nitriding on the biocompatibility of titanium. It also compares plasma-nitrided titanium alloys with alloy steels. It concludes with a short discussion on the effect of nitriding on the surface properties of titanium and two-phase a + ß alloys.

This article addresses the biologic aspects of implant debris both locally and systemically. It discusses the particulate debris, such as stainless steel, cobalt alloy, and titanium alloy, and soluble debris obtained due to wear from all orthopedic implants. Implant debris is known to cause local inflammation, local osteolysis, and, in some cases, local and systemic hypersensitivity. The article describes debris-induced local effects, particle-induced proinflammatory responses, and debris-induced systemic effects. It concludes with a discussion on the four systemic effects of implant debris, namely, neuoropathic effects, hypersensitivity effects, carcinogenictiy, and general toxicity.

Total joint replacement in orthopedic surgery can be achieved by excision, interposition, and replacement arthroplasty. This article details the most common materials used in total replacement synovial joints, such as metals, ceramics, and ultrahigh molecular weight polyethylene (UHMWPE). The principal physical properties and tribological characteristics of these materials are summarized. The article discusses the pin-on-disk experiments and pin-on-plate experiments for determining friction and wear characteristics. It details the use of various types of joint simulators, such as hip joint simulators and knee joint simulators, to evaluate the performance of engineering tribological components in machine simulators. The article describes in vivo assessment of total joint replacement performance.

This article reviews the friction and wear of various dental materials that have been studied by fundamental wear measurements, simulated service wear measurements, and clinical measurements. The materials include dental amalgam, composite restorative materials, pit and fissure sealants, dental cements, porcelain and plastic denture teeth, dental feldspathic porcelain and ceramics, endodontic instruments, periodontal Instruments, and orthodontic wires. The article describes the correlations of properties, such as hardness, fracture toughness, and wear. It discusses wear mechanism such as sliding adhesive wear, two-body abrasion, three-body abrasion, erosion, and fatigue.

This article reviews some concepts considered important for an understanding of processes used for preparing cobalt-chromium alloy implants, the microstructures resulting from this processing, and the resulting material properties. The review includes the solidification of alloys, diffusionless (martensitic) phase transformation as occurs with face-centered cubic to hexagonal close-packed transformation in cobalt-chromium alloys, stacking faults and twins and their role in this transformation. It also includes strengthening mechanisms that are responsible for the mechanical properties of cast and wrought cobalt alloys. The article contains tables that list the commonly used cobalt alloys and their biomedical applications and chemical compositions. It discusses the mechanical and corrosion properties of cobalt alloys, and provides a description of the microstructure of cobalt alloys.

This article provides an overview of the fundamentals of tribology. It describes the advantages, disadvantages, and applications of pin-on-disk method, which is the most commonly used configuration for testing biomaterials and for the reproducible measurement of friction and wear. The article illustrates practical tribocorrosion setup that allows the user to perform wear tests in corrosive environments under well-defined electrochemical conditions and at controlled temperature. It describes the effect of changes in electrical contact resistance on tribological mode. The article discusses various in vivo environmental conditions in tribological tests. Some typical examples of biomaterials testing are also provided.

This article reviews the corrosion interactions between biomedical alloys, in particular iron-base, titanium-base, and cobalt-base alloys, in complex geometries and in applications where there are significant cyclic stresses and potential for wear and fretting motion. It discusses the nature of these metal surfaces and their propensity for corrosion reactions when combined with similar or different alloys in complex restrictive environments within the human body, and under loading conditions. The article describes factors that influence mechanically assisted crevice corrosion. It reviews tests, such as scratch test and in vitro fretting corrosion test, developed to investigate the aspects of mechanically assisted corrosion of metallic biomaterials.

This article provides a summary of biocompatibility or biological response of metals, ceramics, and polymers used in medical implant, along with their clinical issues. The polymers include ultrahigh-molecular-weight polyethylene, nonresorbable polymer, and resorbable polymers.