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

圆盘式滚动接触试验装置是一种新型的陶瓷材料接触试验装置。针对两种类型的氮化硅（sialon和等离子喷涂氧化铝）涂层材料，进行了滚动接触疲劳试验，研究脆性材料的接触疲劳机理。此外，还对氮化硅涂层和氧化铝涂层进行了针盘式磨损试验。两种类型的陶瓷都表现出与金属材料相似的疲劳行为。从断口学和金相观察发现，氮化硅在滚动接触下的裂纹萌生是由循环次表面剪切应力引起的，这在钢轴承中是众所周知的。在最终破坏前的卸荷试件中部，在波动荷兹剪应力最大的深度处，发现了许多平行于接触面的地下微裂纹。通过多个试样验证了微裂纹随循环次数的增加而扩展。高频率轧制试样的失效寿命较短。虽然陶瓷在脉动单轴应力下的循环疲劳似乎是由环境辅助开裂控制的，但这些滚动接触疲劳的实验结果表明，在剪切和压缩应力的混合应力状态下，陶瓷的循环依赖型疲劳是可能的。在氧化铝喷涂层中，随着循环次数的增加，滚动接触疲劳强度也随之降低。断裂起始于氧化铝和钼层之间的界面。氮化硅涂层和氧化铝涂层在水中高速摩擦条件下均表现出较高的耐摩擦磨损性能。

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.