Wear in which hard particles or hard asperities on the counterface scratch and cut material from a softer surface. It drops greatly when the surface is made harder than the particles.
Japanese name: アブレシブ摩耗
Abrasive wear appears in 2 practice questions across 1 topic, including Surface treatment and tribology.
Abrasive wear includes two-body abrasive wear, in which hard asperities on the counterface or fixed abrasive grains scratch the surface, and three-body abrasive wear, in which hard particles trapped between two surfaces roll and slide while cutting the surface. Wear by a file or a grinding wheel is two-body; sand, dirt or wear particles mixed into lubricating oil scratching surfaces inside a bearing are examples of three-body wear. In three-body wear the particles spend more time rolling and cut less efficiently, so the wear is often about an order of magnitude less than in two-body wear. Keeping hard particles out by oil filtration and seals is the basic way to prevent three-body wear.
When a hard particle scratches a surface, material is removed in three ways: microploughing, which pushes material aside into ridges on both sides of the groove; microcutting, which removes material like a chip; and microcracking, in which brittle materials chip off by fracture. The sharper the particle's corners and the steeper the angle at which it meets the surface, the more likely cutting becomes and the more the wear increases. In ploughing, material is not lost immediately, but only once the ridges, rubbed again and again, detach by fatigue. In ductile metals ploughing and cutting dominate, and in brittle materials such as ceramics wear by cracking dominates.
The basic way to reduce abrasive wear is to make the surface harder than the particles, but hardness alone does not decide the result. In materials containing hard carbides, such as high-chromium cast irons, the size and amount of the carbides matter: if the carbides are smaller than the width of the grooves the particles make, they are cut away together with the soft surrounding matrix. Conversely, if the carbides are large and well supported by the matrix, the particles hit the carbides and stop. Also, hard but brittle materials crack and chip in wear involving large impacts, so for high-impact uses materials are chosen with the balance against toughness in mind.
Abrasive wear is evaluated with tests such as one that feeds dry sand between a rubber wheel and the specimen and measures the wear (ASTM G65), and tests that slide the specimen on abrasive paper. In construction and mining machinery that handles earth and rock, agricultural implements and pipes conveying powders, abrasive wear often determines the life of parts. On the other hand, grinding, polishing and lapping are processes that deliberately use the mechanism of abrasive wear. By choosing the size and hardness of the abrasive grains and the pressing force, they adjust the removal rate and the roughness of the finished surface.
Answer: A. Raising the surface hardness to about that of the sand grains or higher makes it hard for the grains to dig into the surface and reduces wear greatly
Empirically, a grain must be about 1.2 times harder than the surface (Ha ≥ about 1.2Hs) to scratch it, and once the surface hardness Hs is raised so that Hs/Ha exceeds about 0.8, abrasive wear drops sharply. The grains can no longer dig into the surface, and their corners are crushed instead. For this reason, high-chromium cast irons containing much Cr carbide (about 1200–1800 HV), which is harder than quartz, hardfacing welds containing WC, and ceramic coatings are used. Martensite in hardened steel is around 900 HV even at high carbon, about as hard as quartz or softer, so it raises wear resistance but does not eliminate wear. The amount of wear is proportional to the sliding distance, but hardness also has a large effect, so it is not independent of hardness.
Hardness is the most important factor, but it is sometimes not enough on its own. The size and distribution of hard phases, the strength of the matrix and toughness against impact also matter, and brittle materials chip under impact. Materials are chosen to suit the service conditions, such as the hardness and size of the particles and how they strike.
Erosion is wear in which particles carried by a fluid strike and cut a surface; the way force is applied differs from abrasive wear, in which particles are pressed against the surface and slide. In erosion the impact angle has a large effect: ductile materials wear most at shallow angles, and brittle materials at angles close to perpendicular.
It is estimated with V = KWL/H, the same form as Archard's equation, so the wear is proportional to load and sliding distance and inversely proportional to hardness. If the particles are modeled as cones, K is set by the sharpness of the particle corners and is larger the sharper they are. Real values of K vary greatly with conditions, so they are found by testing.
Empirically, a grain must be about 1.2 times harder than the surface (Ha ≥ about 1.2Hs) to scratch it, and once the surface hardness Hs is raised so that Hs/Ha exceeds about 0.8, abrasive wear drops sharply.
A construction-machine part is rubbed by soil containing qu…Hard particles or asperities cutting a surface is abrasive wear, and cracks growing from below the surface under repeated contact stress until flakes come off is fatigue wear (fatigue pits and spalling), seen in bearings and gears.
Which of the following descriptions of wear mechanisms corr…Martensite Adhesive wear Archard wear equation Carburizing Electroless nickel plating Nitriding Real area of contact Stribeck curve