Fracture behavior of a Ni-20 wt.%Cr binary alloy processed by Laser Powder Bed Fusion: Influence of the specimen building orientation and rotation angle between layers

Abstract

This work provides a comparative study on the influence of the manufacturing process on the tensile and fracture properties of a Ni-20 wt.%Cr binary alloy produced by Laser Powder Bed Fusion (L-PBF). Two main processing parameters were investigated: the orientation of the samples with respect to the building direction (horizontal and vertical) and the rotation angle between layers (67° and 90°). Tensile and three-point bending tests were conducted to study the mechanical behavior. Monotonic tensile results suggest that the choice of the printing parameters affected the yield and ultimate tensile strength values, but was not influential to elongation. An increase in yield and ultimate tensile strengths of up to 15 % was noted for horizontal specimens compared to the vertical ones, and an increase of 10 % for an angle of 67° rather than 90°. Fracture toughness values remained in a range of 200 to 450 kJ/m2 regardless of the set of parameters considered. For a rotation angle of 67°, the fracture toughness was similar for both building orientations, but vertical specimens exhibited better resistance to crack propagation after initiation, with a tearing modulus increased by 50 % compared to horizontal ones. In contrast, building orientation was detrimental to specimens built with a rotation angle of 90°, as both fracture toughness and tearing modulus decreased drastically (up to 70 %) for a horizontal orientation rather than a vertical one. Microstructural observations highlighted mixed fracture modes for all L-PBF configurations, though crack propagation seemed mainly intergranular for horizontal specimens, and transgranular for vertical specimens. Fracture mechanisms were mostly governed by the grain orientation, size and morphology, while the crystallographic texture and the nano-oxides located in the dendrite arm spacing had a second-order influence. The pores and meltpool boundaries did not appear to play a significant role in crack propagation.