Abstract
Post-sintering plasma surface treatments permit a considerable improvement in fatigue and wear properties of powder-metallurgy products. However, the fracture micromechanisms involved have as yet not been clearly established. With this purpose a scanning-electron fractographic analysis was performed on fatigue-ruptured specimens, either with or without plasma nitriding. Two different treatment atmospheres were employed. Results show that nitriding increases fatigue life, in connection with the operation of peculiar fracture micromechanisms, the nature, frequency,location and extent of which depend on the base material, nitriding atmosphere and, in some cases, also on local porosity features.