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Surface treatment and tribology

Which of the following descriptions of wear mechanisms corresponds to adhesive wear?

  1. AHard particles or hard asperities on the counterface scratch and cut material away from a softer surface
  2. BContact stresses repeated in rolling contact and the like create cracks below the surface, and the surface layer comes off in small flakes
  3. CMetals bond strongly at the real contact spots, and when sliding shears the junctions, material from one side transfers to the other or detaches to form wear debris
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Answer: C. Metals bond strongly at the real contact spots, and when sliding shears the junctions, material from one side transfers to the other or detaches to form wear debris

Adhesive wear occurs when surface atoms bond at the real contact spots (microscopic welding), and when sliding shears the junctions, material tears out of the weaker side, transfers to the counterface and eventually detaches as wear debris. It is severe between clean metals of the same kind and in bad cases leads to seizure. It can be reduced by pairing metals with little mutual solubility, and by lubricants and oxide films. 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. In real wear, several of these mechanisms often act at the same time.

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More Surface treatment and tribology questions

  1. A construction-machine part is rubbed by soil containing quartz sand grains (hardness about 1000 HV). Which is the correct way to choose a material that reduces abrasive wear?
  2. In a pin-on-disk test, a pin of hardness H = 2.0 GPa is loaded with a normal force of 50 N and slid over a distance of 1.0 km. Using the Archard wear equation V = KWL/H with a dimensionless wear coefficient K = 1.0×10⁻⁴, which correctly pairs the wear volume of the pin with the change in wear volume when the load is doubled?
  3. Which statement correctly describes the Stribeck curve, which plots the friction coefficient of a plain bearing against the bearing characteristic number ηN/P formed from the lubricant viscosity η, the rotational speed N and the bearing pressure P?
  4. In a rolling bearing, the minimum oil film thickness is h = 0.40 µm and the root-mean-square roughnesses of the two surfaces are Rq1 = 0.15 µm and Rq2 = 0.20 µm. Find the film thickness ratio λ = h/√(Rq1² + Rq2²) and, taking λ < 1 as boundary lubrication, 1–3 as mixed lubrication and above 3 as hydrodynamic (full-film) lubrication, choose the correct pairing.
  5. A plain bearing with an inner diameter of 40 mm and a width of 30 mm carries a radial load of 1.2 kN, and the shaft turns at 600 rpm. Taking the bearing pressure P as the load divided by the projected area (inner diameter × width) and the sliding speed v as the surface speed of the shaft, which is closest to the PV value?