Research Progress on the Recast Layer of a Cooling Hole by Electro-Discharge Machine

Author of the article:LIU Lu1 , YANG Zenan2 , LI Junjie1 , WANG Zhijun1

Author's Workplace：1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China; 2. Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China

Key Words：turbine blades; film cooling holes; electrodischarge machine; recast layer

Abstract：Film cooling holes (FCHs) have been widely used in turbine blades of air engines, playing a vital role in raising the engine service temperature. Electrodischarge machining (EDM) has become one of the main methods for processing FCHs with high efficiency and quality. However, the recast layer (RL) is usually inevitable around the FCHs by EDM, which is formed by the ultrafast solidification of the molten metal during processing. Research on RL has gained important attention in the aviation field because it affects not only the cooling efficiency but also the service performance of blades. This paper summarizes the research progress of FCHs and RL processed by EDM and introduces the evolution and microstructure characteristics of the recast layer. At the same time, with the goal of processing “FCHs without RL”, we review some process optimization methods for processing FCHs by EDM. All the studies show that an understanding of the RL is beneficial to further utilize process optimization to control and eliminate the RL thickness