An assessment of spall failure modes in laser powder bed fusion fabricated stainless steel 316L with low-volume intentional porosity

This paper reports on spall failure and damage modes in Laser Powder Bed Fusion fabricated Stainless Steel 316L (SS316L) with intentional levels of low-volume (1–5 vol. %) porosity and pore sizes of 200, 350, and 500 μm. The fabricated specimens were subjected to uniaxial-strain plate-impact loading...

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Bibliographic Details
Published in:Journal of applied physics 2023-05, Vol.133 (18)
Main Authors: Koube, K. D., Sloop, T., Lamb, K., Kacher, J., Babu, S. S., Thadhani, N. N.
Format: Article
Language:English
Subjects:
Applied physics
austenitic stainless steels
Crack initiation
Crack propagation
Cracking (fracturing)
crystal twinnings
deformation
EBSD
electron backscatter diffraction
Failure analysis
Failure mechanisms
Failure modes
Fracture mechanics
Free surfaces
Impact loads
Laser damage
laser powder bed fabrication
MATERIALS SCIENCE
Microstructure
Nucleation
Pore size
Porosity
porous media
Powder beds
scanning electron microscopy
shock compression
shock waves
spall failure
spalling
Stainless steel
Stainless steels
Tensile stress
Velocimetry
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Summary:This paper reports on spall failure and damage modes in Laser Powder Bed Fusion fabricated Stainless Steel 316L (SS316L) with intentional levels of low-volume (1–5 vol. %) porosity and pore sizes of 200, 350, and 500 μm. The fabricated specimens were subjected to uniaxial-strain plate-impact loading at ∼4.5 GPa, to initiate incipient spall failure. Analysis of velocimetry profiles measured using multi-probe photon-Doppler velocimetry coupled with post-mortem analysis of soft-recovered samples reveals local suppression of spall failure (termed as spall-dominated) as a function of porosity, as the failure mechanism transitions from spall-centered tensile stress dominated to a pore-centered microstructure-dominated damage mode involving void/crack nucleation and growth at pre-existing pores. The critical porosity level where the suppression of spall failure is first observed, as well as the spall location, is dependent on both the volume fraction and the size of the initially fabricated pores. In samples of 500 μm pore size, the suppression of spall failure is observed with as little as 1 vol. % porosity, while samples with smaller pores (200 μm) still experience spall-centered tensile stress dominated failure with higher levels (5 vol. %) of porosity. In the case of pore-centered microstructure-dominated failure, spall damage can occur but the spall plane is shifted toward the rear free surface, or more generally in areas further away from the region with pores. Highly heterogeneous deformation twinning, shear banding, grain rotation, and cracking are observed in the vicinity of pre-existing pores and expected spall failure sites.
ISSN:0021-8979
1089-7550
DOI:10.1063/5.0143744