Subsurface zone detected in pure nickel by positron annihilation; Hall-Patch effect notification

A dry sliding test and sequential etching technique, combined with positron lifetime measurements on pure nickel, revealed an area of damage below the worn surface extending to a depth of hundreds of micrometers. Some correlation was found between the value of the mean positron lifetime measured directly on the worn surface and the coefficient of friction. The obtained dependency rather confirms the normal Hall-Patch regime. There was no correlation with the specific wear rate.