Surface integrity characterization of third-generation nickel-based single crystal blade tenons after ultrasonic vibration-assisted grinding
Biao Zhao, Hexu You, Qing Miao, Wenfeng Ding, Ning Qian, Jiuhua Xu
Abstract
Machined surface integrity of workpieces in harsh environments has a remarkable influence on their performance. However, the complexity of the new type of machining hinders a comprehensive understanding of machined surface integrity and its formation mechanism, thereby limiting the study of component performance. With increasing demands for high-quality machined workpieces in aerospace industry applications, researchers from academia and industry are increasingly focusing on post-machining surface characterization. The profile grinding test was conducted on a novel single-crystal superalloy to simulate the formation of blade tenons, and the obtained tenons were characterized for surface integrity elements under various operating conditions. Results revealed that ultrasonic vibration-assisted grinding (UVAG) led to multiple superpositions of abrasive grain trajectories, causing reduced surface roughness (an average reduction of approximately 29.6%) compared with conventional grinding. After examining the subsurface layer of UVAG using transmission electron microscopy, the results revealed that the single-crystal tenon grinding subsurface layer exhibited a gradient evolution from the near-surface to the substrate. This evolution was characterized by an equiaxed nanocrystalline layer measuring 0.34 μm, followed by a sub-microcrystalline grain-forming zone spanning 0.6 μm and finally, a constituent phase-twisted distorted deformation zone over 0.62 μm. Under normal grinding conditions, the tenon exhibited low surface hardening (not exceeding 15%), and residual compressive stresses were observed on its surface. In cases where grinding burns occurred, a white layer appeared on the tenon’s surface, which demonstrated varying thicknesses along the teeth from top to root due to thermal-force-structural coupling effects. Additionally, these burns introduced residual tensile stresses on the tenon’s surface, potentially substantially affecting its fatigue life. This paper enhances our understanding of UVAG processes and establishes a foundation for their application in manufacturing single-crystal turbine blades for next-generation aero-turbine engines.