Direct laser deposition of Inconel 738 on directionally solidified Ni-base superalloy component

Abstract

This paper presents the research on direct laser deposition of Inconel 738 alloys on directionally solidified (DS) Ni-base supperalloy substrate in order to strengthen or repair the DS gas turbine blades. The results indicate that cracks occur very easily during the deposition process and cracks in laser deposited Inconel 738 on DS Ni-base supperalloy substrate are mostly thermal cracks which may originate on the interface between deposited layers and DS substrate, and develop to multi-deposited layers. The low melting temperature point eutectics between the grain boundaries of DS Ni-base superalloy substrate are the main sources of thermal cracks. Strict control of the heat input of the deposition process can dramatically decrease the cracking tendency. Layers with the DS characteristics are achieved by direct laser deposition on Ni-base superalloy substrate with good shaping and free of cracks by optimizing the deposition technique and laser parameters. Compared with the substrate, the microstructure of the layers is much finer, the average primary spacing of the dendrites is about 5μm. The microhardness of Inconel 738 multi-deposited layers is very uniform, indicating the structure of the layers is homogeneous. The results demonstrate the feasibility and great foreground in repairing and fabricating local parts on DS Ni-base superalloy turbine blades by direct laser fabrication technology.