A Study on Surface Durability of Ion-Nitrided Sintered Powder Metal Rollers : Influence of Particle Diameter of Powder and Relationship Between Surface Durability and Hardness

In order to evaluate the surface durability of ion-nitrided sintered powder metal rollers, the influence of particle diameter on the surface durabilities of the sintered rollers was investigated under a sliding-rolling contact condition. The failure mode of the rollers was spalling due to subsurface cracks. The surface durability of the roller became higher as the particle diameter became smaller. The spalling failure depth agreed almost with the depth where the amplitude A(τyz/Hν) of the ratio of orthogonal shear stress to Vickers hardness became peak. The surface durability was evaluated using the amplitude A(τyz) of the shear stress and the hardness Hν at the peak amplitude of A(τyz/Hν). The relationship between A(τyz) and Hν of the sintered rollers and gears having medium pore distribution was given by an equation A(τyz)=0.174Hν1.13. However, the relationship of the sintered rollers and gears having different pore distribution did not conform to the above equation. Therefore, it could be said that the surface durability of the sintered roller depended on the pore distribution.