GSD-18 EFFECT OF SURFACE MODIFIED LAYER ON ROLLING FATIGUE STRENGTH(GEAR STRENGTH AND DURABILITY)

Abstract

Surface modified rollers and ball bearings were fatigue-tested under pure rolling contact conditions. Electroless Ni-P alloy plating and sulfurizing treatments were employed. Failure mode of all rollers and bearings was spalling/flaking due to subsurface cracking. Fatigue lives of both rollers and bearings were improved by surface modifications. The influence of elastic modulus of a plated layer on contact pressure and subsurface stresses was examined under line contact and point contact conditions. The contact pressure and subsurface stresses were reduced by the soft surface modified layer, especially at the edge of the contact width under the line contact condition. The conformity due to wear of the plated layer led to the reduction of the contact pressure and the subsurface stresses. The reason why the rolling fatigue strengths of surface modified rollers and bearings were higher than those of the non-coated ones would be due to the smaller contact pressure and the smaller subsurface stresses by the smaller elasticity as well as the conformity of the plated layer.