Application of laser powder deposition for turbine blade tip cap freeform fabrication

This paper presents a laser powder deposition based manufacturing method for freeform fabricating a new tip cap or restoring/repairing an existing tip cap on high pressure turbine blade airfoil. Cast turbine airfoils for advanced gas turbine engines have internal features that challenge the capability of current casting technologies. Conventional way of manufacturing HPT blade involves casting the entire blade airfoil including the tip cap as an integral part with sacrificial ceramic cores to form the complex internal features. These cores are fragile and prone to shift during the casting process, which leads to low yield (50-70%) of the casting process. The post-cast leaching and core cleanout processes are time consuming due to the enclosed complex internal cavities of blade. To cast the HPT blade with open tip and then form the tip cap structure on the cast airfoil using laser powder deposition technique can potentially improve the cast yield and reduce the production cycle time while maintaining the metallurgical integrity of the finished part. Methods are presented in this paper to form an overhanging tip cap structure on a HPT blade airfoil directly from metal powder. A metallurgical bonding is formed between the blade base material (alloy A) and the tip cap material (alloy B).