Wear failures Wear, friction, and lubrication are complex, interwoven subjects that may all affect the tendency of a part to fail or to ease being able to perform its intended function. While all three are very important, only wear receives emphasis in this ection,while friction and lubrication are covered less extensively. The science of wear is called tribology, from the Greek word tribos, meaning wear, and it forms the basis for a systems approach to wear failure analysis A systems approach to wear is necessary to understand the interactions among The system material components-the bulk and surface properties of the wearing parts, the properties of the material causing the wear, and the interface medium The operating variables The interactions among the material components of the system The operating environment It should already be clear that wear failures are not easy to analyze, describe, or prevent. There is no general agreement even as to the various types or forms of wear because they can be described in several different ways. One relativel This section discusses these eight form of wear, as follow. Sed by wear is to describe eight major forms or mechanisms simple way to classify the mechanical surface damage ca abrasive wear Erosive wea Adhesive wear Frett Cavitation Liquid-droplet impingement Corrosive wear About half of all wear failures are caused by abrasive wear, 15% by adhesive wear, and about 8% each by erosion and fretting. The other four mechanisms account for the remaining wear failures the characteristics and mitigation of each are briefly described in the following section, along with lubricant failures Types of Wear Abrasive Wear. The principal mechanism of abrasive wear is indicated by cutting. Abrasive wear is sometimes referred to as grinding wear. High-stress, low-speed particles or projections from hard materials cut and plow small grooves in softer materials. This type of wear is characteristic of damage to many ground contact tools, such as plows and cultivators, as well as other parts that dig into or rub against hard, abrasive materials. Again, it can lead to complete or partial failure and destruction of the part, particularly with respect to cutting tools, which can be badly dulled Abrasive wear can be mitigated by changing material to High-carbon steel 20 to 30% Cr white cast iron wC or TiC composites and by increasing surface hardness using Hard chrome plate Hardfacing alloy weld overlay Electroless nickel-phosphorus alloy plate High-velocity oxyfuel(HVOF)ceramic coatings(WC, CrC, aluminum oxide) Lubrication is of marginal use in combating abrasive wear, unless a lubricant layer thicker than the particle size can be maintained. Further examples and details are given in the article" Abrasive Wear Failures""in this volume Erosive wear is similar to abrasive wear, except that the force is provided by the kinetic energy of the particles as they are carried in a fluid. Low-stress, high-speed particles impinge upon the surface at some angle, tending to cut( ductile metal) or fracture(brittle material)very small wear chips, or particles from the surface. Erosion is a particular problem with various types of impellers, propellers, fans, and other parts where particles in a fluid, such as air or water, strike theWear Failures Wear, friction, and lubrication are complex, interwoven subjects that may all affect the tendency of a part to fail or to cease being able to perform its intended function. While all three are very important, only wear receives emphasis in this section, while friction and lubrication are covered less extensively. The science of wear is called tribology, from the Greek word tribos, meaning wear, and it forms the basis for a systems approach to wear failure analysis. A systems approach to wear is necessary to understand the interactions among: · The system material components—the bulk and surface properties of the wearing parts, the properties of the material causing the wear, and the interface medium · The operating variables · The interactions among the material components of the system · The operating environment It should already be clear that wear failures are not easy to analyze, describe, or prevent. There is no general agreement even as to the various types or forms of wear because they can be described in several different ways. One relatively simple way to classify the mechanical surface damage caused by wear is to describe eight major forms or mechanisms. This section discusses these eight form of wear, as follows: · Abrasive wear · Erosive wear · Adhesive wear · Fretting · Cavitation · Liquid-droplet impingement · Rolling-contact fatigue · Corrosive wear About half of all wear failures are caused by abrasive wear, 15% by adhesive wear, and about 8% each by erosion and fretting. The other four mechanisms account for the remaining wear failures. The characteristics and mitigation of each are briefly described in the following section, along with lubricant failures. Types of Wear Abrasive Wear. The principal mechanism of abrasive wear is indicated by cutting. Abrasive wear is sometimes referred to as grinding wear. High-stress, low-speed particles or projections from hard materials cut and plow small grooves in softer materials. This type of wear is characteristic of damage to many ground contact tools, such as plows and cultivators, as well as other parts that dig into or rub against hard, abrasive materials. Again, it can lead to complete or partial failure and destruction of the part, particularly with respect to cutting tools, which can be badly dulled. Abrasive wear can be mitigated by changing material to: · High-carbon steel · 20 to 30% Cr white cast iron · WC or TiC composites and by increasing surface hardness using: · Hard chrome plate · Hardfacing alloy weld overlay · Electroless nickel-phosphorus alloy plate · High-velocity oxyfuel (HVOF) ceramic coatings (WC, CrC, aluminum oxide) Lubrication is of marginal use in combating abrasive wear, unless a lubricant layer thicker than the particle size can be maintained. Further examples and details are given in the article “Abrasive Wear Failures” in this Volume. Erosive wear is similar to abrasive wear, except that the force is provided by the kinetic energy of the particles as they are carried in a fluid. Low-stress, high-speed particles impinge upon the surface at some angle, tending to cut (ductile metal) or fracture (brittle material) very small wear chips, or particles from the surface. Erosion is a particular problem with various types of impellers, propellers, fans, and other parts where particles in a fluid, such as air or water, strike the