Introduction/Purpose

The study of thin-walled structure improves the design freedom of additive manufacturing. Understanding the relation between anisotropic mechanical properties and microstructure gives better control on manufacturing process and challenges the limit of the practical application. As one of the key Ni-based superalloy in aerospace industries, thin-walled Hastelloy X will be beneficial to the light weight application and build a more sustainable environment.

Methods

Thin-walled structures with different thickness form 1mm to 4mm was built by Selective Laser Melting process from EOS M290 machine, and the used powder was EOS NickelAlloy HX. The microstructure and crystallographic orientation have been studied by SEM and EBSD. Tensile tests with directions parallel and perpendicular to building direction (BD) have been carried out at elevated temperature from 400˚C to 700˚C.

Results

The elongated grains have been observed partly parallel and partly 45˚ tilted to the BD from back scattered SEM images, and the contouring region shows smaller grain size . Along the BD, the major preferred orientation is <101> and the minor is <001>. The tensile test result indicates higher strength but lower elongation in the direction perpendicular to BD, and also a big elongation drop between 600˚C and 700˚C. EBSD result from highly deformed area shows different texture evolution mechanism between two different tensile directions.

Conclusions

The local thermal gradient created by the scanning strategy guides the grain growing direction, which is <001>, and <101> turns to be the preferred orientation along BD. The elongated grains are the main reason for the anisotropic mechanical properties. When the tensile direction is parallel to BD, the orientation evolution fits the theory and indicates lattice rotation.