Sealing to improve the wear properties of plasma sprayed alumina by electro-deposited Ni

Electro-deposition of Ni has been used in an attempt to seal the open porosity of plasma sprayed alumina coatings. By means of scanning electron microscopy, the open porosity was found to be completely sealed. The as deposited and sealed coatings have been evaluated and compared by scratching, abrasion, particle erosion and sliding wear tests to determine the effects of the sealing treatment on the tribological properties. Also, studies of Vickers indentations were performed to assess the effect of the sealing on crack propagation. The mechanisms of damage including wear have been identified and discussed. It is concluded that electro-deposition of Ni is a promising sealing treatment for sprayed alumina coatings intended for tribological applications. The hardness increased and the wear resistance was found to increase markedly in all wear tests as a result of the sealing.