粉末高温合金FGH4096的疲劳小裂纹扩展行为  

Propagation Behaviors of Small Cracks in Powder Metallurgy Nickel-Based Superalloy FGH4096

作　　者：杨秦政 杨晓光[2] 黄渭清 石多奇[1,2] YANG Qinzheng;YANG Xiaoguang;HUANG Weiqing;SHI Duoqi(School of Energy and Power Engineering,Beihang University,Beijing 102206,China;Beijing Key Laboratory of Aero-Engine Structure and Strength,Beihang University,Beijing 100191,China;School of Mechanical Engineering,Beijing Institute of Technology,Beijing 100081,China)

机构地区：[1]北京航空航天大学能源与动力工程学院,北京102206 [2]北京航空航天大学航空发动机结构强度北京市重点实验室,北京100191 [3]北京理工大学机械与车辆学院,北京100081

出　　处：《金属学报》2022年第5期683-694,共12页Acta Metallurgica Sinica

基　　金：国家科技重大专项项目No.2017-Ⅳ-0012-0049;国家自然科学基金项目No.51775019。

摘　　要：以粉末高温合金FGH4096为研究对象,开展了2个不同最大应力条件下的疲劳小裂纹扩展实验。利用SEM结合EBSD观察了小裂纹扩展路径,表征了扩展路径上晶粒的取向,重点从小裂纹的三维属性和扩展物理基础出发,研究了小裂纹的扩展和停滞行为。结果表明:小裂纹自萌生到总长度超过1.0 mm后始终保持沿八面体滑移面扩展的行为;晶界和孪晶界是阻碍小裂纹扩展、导致小裂纹扩展停滞的微观组织,这些晶界/孪晶界的M因子都较邻近晶界的M因子低,表明M因子可用作表征晶界/孪晶界阻碍小裂纹扩展的能力。根据晶界性质和载荷的不同,小裂纹在晶界/孪晶界处发生扩展停滞后可以有3种行为:一是在经历一定循环数后,裂纹穿越晶界继续扩展;二是在裂纹停滞期间,裂纹转到所在晶粒内的其他滑移面或沿扩展路径上其他晶粒内的滑移面继续扩展;三是二次裂纹在停滞的主裂纹尖端附近1~2个晶粒范围萌生,并与主裂纹连接后继续扩展成为新的主裂纹,该裂纹行为仅出现在最大应力接近屈服强度范围下限的试样中。Inevitable nonmetallic inclusions(NMIs) exist in powder metallurgy(PM) superalloys.These inclusions serve as preferred sites for crack initiation either by fracture of inclusions or inclusion/matrix decohesion. After initiating from NMIs, fatigue cracks will experience the small crack propagation phase. Small fatigue cracks could grow under the fatigue crack growth threshold and propagate at a vibrated rate. To investigate the propagation behavior and reveal the underlying mechanisms, small crack propagation experiments under fatigue loads of different maximum stresses were conducted on PM superalloy FGH4096 using the small fatigue crack-propagation experiment system. The characterization of microstructure was conducted and orientations of grains were calibrated using SEM integrated with EBSD. Focusing on the three-dimensional nature and the physical basis, the propagation and stagnation behavior of small cracks were revealed. Experimental results showed that the small cracks propagated along octahedral slip planes, from initiation to a length even longer than 1.0 mm. During the propagation in the grain-containing twin, small cracks grew along the direction parallel to the twin boundary. However,several twin boundaries impeded crack growth. Small cracks were stagnated at grain and twin boundaries of which M factors were lower than adjacent ones. Three behaviors were observed after the stagnation of small cracks due to the different properties of grain/twin boundaries and the applied load;first,stagnated small cracks could continue to propagate by consuming more cycles;second, small cracks could propagate by alternating to another slip plane in current or other grains on the crack path;third, secondary cracks would initiate within 1-2 grains from the tip of the fully stagnated cracks and connected to the main crack. This behavior was observed only in the specimen in which the maximum stress is close to the lower limit of the yield strength.

关 键 词：镍基粉末高温合金 疲劳小裂纹 八面体滑移面 

分 类 号：TG146[一般工业技术—材料科学与工程]