Mechanical behavior of 17-4 PH stainless steel processed by atomic diffusion additive manufacturing

This work explores the multiscale mechanical behavior of 17-4 PH stainless steel structures processed through the atomic diffusion additive manufacturing technique (ADAM). 17-4 PH stainless steel parts were fabricated with a Markforged Metal X 3D printer and characterized with respect to variable printing orientations for samples loaded in tension, shear, and bending. Sections of material were taken from each face of a bending test sample and prepared for microscopy to quantify porosity, grain size, and local stiffness and hardness. Microscale evaluation showed a porosity content of 3.3% on average across all faces. The yz face specifically showed the same sort of packing limitations often seen in other extrusion-based methods leading to greater porosity. An electron backscatter diffraction investigation showed a mean grain size of 6.5 μm with some grain alignment in the z-direction in the xz plane. Bulk material response in tension was dependent upon the print orientation of the sample. Cases where material was extruded entirely in the direction of loading saw a stiffness, strength, and strain to failure improvement of greater that 10% compared with other infill schemes. Shear testing revealed similar increases in strain to failure for samples with material extruded in only one direction compared with cross hatching at alternating orthogonal angles. Bend test results were similar in tension and compression regardless of orientation. For a sample printed with primary loading in the print plane (xy), the tensile modulus was 130–140 GPa, the tensile yield and ultimate strength were 600 MPa and 800 MPa, and the shear strength was 40.6 MPa on average.