Effect of crystallographic texture on the anisotropic mechanical behaviour of additively manufactured Ni-based superalloy

Cheng-Han Yu, Ru Lin Peng, Johan Moverare

Linköping University

Introduction 

Materials manufactured by powder bed fusion often exhibit anisotropic mechanical behaviour depending on the building direction, the characteristic grain structure and texture created by the directional energy input play an important role in this behaviour. This study elaborates the deformation mechanisms of Hastelloy X by bridging the mechanical testing and microstructural study.  

Experiments 

Plate-like specimens with different thicknesses (1mm - 4mm) were built by laser powder bed fusion, and two types of tensile specimens were taken from the plates where “Vertical” tensile specimens refer to the loading direction being parallel to the building direction and the two directions are perpendicular to each other for “Horizontal” tensile specimens.  

Hot tensile tests (RT – 700˚C) and slow strain rates tensile tests (SSRT, 10-5/s and 10-6/s) were applied to the as-built tensile specimen without post-treatment. The texture and microstructural evolution at different levels of induced plasticity were studied by using neutron diffraction, SEM, EBSD and TEM.  

Highlights 

• The “Vertical” deformation behaviour resembles single crystalline materials, while the “Horizontal” deformation behaviour resembles polycrystalline materials.  
• Crystallographic-dependent twinning induced plasticity (TWIP) effect was observed in the SSRT, which the TWIP effect has not been found in conventionally manufactured Hastelloy X due to the high stacking fault.  
• A thickness-dependent texture behaviour was discovered, and a roughness calibration  method is proposed to tackle the rough as-built surface.  

In general, the deformation behaviours under different testing conditions will be presented in the poster.