Rolling Contact Fatigue and Contact Wear of Ceramics and Plasma Sprayd Ceramic Coating

点击翻译按钮获取中文摘要

Disk-type rolling contact test apparatus has been newly developed for ceramic materials. For two types silicon nitrides, a sialon and a plasma sprayd alumina coating material, rolling contact fatigue tests were performed to investigate mechanisms of contact fatigue for brittle materials. Furthermore, pin-on disk type wear tests were performed for the silicon nitride and the alumina coating.Both type of ceramics showed a fatigue behavior similar to that of metallic materials. From fractographic and metallographic observations, it has been found that the crack initiation in the silicon nitrides subjected to rolling contact is induced depending on cyclic subsurface shear stress, as is known in steel bearings. On the mid sections of off-loaded specimens before the final failure, many subsurface micro cracks which lay parallel to the contact surface were found at depth where the fluctuated Herzian shear stress was maximum. Growth of these micro cracks with the increase of cyclic number was confirmed using multiple specimens. The specimens subjected to higher frequency rolling gave shorter failure lives. Although the cyclic fatigue of ceramics under pulsating uniaxial stress seems to be governed by environmentally assisted cracking, these experimental results in rolling contact fatigue suggest that cyclic dependent type of fatigue in ceramics is alternatively possible under the mixed stress state of shear and compressive stresses.In alumina sprayd coating, rolling contact fatigue strength was also decreased with the increase of cyclic number. Fracture initiated from the interface between the alumina and Mo interlayr. Both of the silicon nitride and the alumina coating show high resistance for friction wear under the condition of high velocity friction in water.