John E Kelley and Jacob J Stiglich

Wear Technology, Inc.

Abstract

The wear testing of coatings, surface modifications, and hardfacing materials presents a number of problems that can lead to an inaccurate assessment of their wear behavior. A discussion of several wear testing problems is given, along with pertinent examples and some techniques for preventing or minimizing the problems.

Hundreds of wear tests have been devised for evaluating the wear characteristics of every class of material. A few test methods that have been successfully applied to coatings and surface modifications, some standardized and some not, are presented.

Introduction

The past decade has seen a great increase in developments of specialized coatings and surface modifications. From automotive to aerospace—textiles to energy conversion. Most industries have benefitted from these developments. Engineered surfaces represent many materials types; metals and alloys» ceramics, cermets, intermetallic compounds, composites and polymers. The fabrication methods, some old and some new, also are many; flame spray coating, laser surface treating, ion-implantation, diffusion alloying, electroplating, electroless plating, overlay welding, plasma spray coating, chemical vapor deposition, r.f. sputter coating, slurry coating, electric spark deposition, brazing fused salt electrolysis, explosive and roll bond cladding, and vacuum evaporation. Along with these innovations in surface engineering has come the need for properly evaluating the wear properties of many dozens of new materials. Frequently, the results of evaluation of wear behavior of coatings and modified surfaces are misleading and inaccurate. The selection of inappropriate wear test methods and procedures, and/or the lack of knowledge of potential problems inherent to testing of coatings can lead the researcher astray. The purpose of this discussion is to point out several problem areas in wear testing of coatings, define some solutions to these problems, and to recommend several wear test methods that have been used successfully to study erosion, high stress abrasion, low stress abrasion, sliding wear, and friction of coatings, surface modifications, and hardfacings.

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