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

新型陶瓷材料滚动接触试验装置是一种新型的陶瓷材料滚动接触试验装置。对Sialon和等离子喷涂Al 2 O3两种氮化硅涂层材料进行了滚动接触疲劳试验，研究了脆性材料的接触疲劳机理。此外，对氮化硅和氧化铝涂层进行了销-盘型磨损试验，两种陶瓷都表现出类似于金属材料的疲劳行为。从断口和金相观察，它已被发现，在氮化硅受到滚动接触的裂纹萌生诱导取决于循环次表面剪切应力，如已知的钢轴承。在卸载试样的中间部分，在最终失效之前，许多亚表面的微裂纹平行于接触表面被发现的深度波动的赫兹剪应力是最大的。使用多个试样证实了这些微裂纹随着循环次数的增加而增长。经受较高频率轧制的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，陶瓷在剪切和压缩应力的混合应力状态下可能交替地出现循环依赖型疲劳，在氧化铝喷涂涂层中，滚动接触疲劳强度也随着循环次数的增加而降低。断裂起始于氧化铝和钼中间层之间的界面。在水中高速摩擦条件下，氮化硅涂层和氧化铝涂层均表现出良好的耐磨性。

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.