Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using...

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• Understanding stacking fault energies (SFE) is crucial for predicting mechanical behavior in advanced alloys.
• Additively manufactured (AM) materials like SS 316L and CrCoNi alloys exhibit unique microstructures that can influence SFE.
• Deformation mechanisms, such as dislocation slip and twinning, are strongly dependent on SFE.

Purpose of the Study:

• To determine the SFE in additively manufactured SS 316L and equiatomic CrCoNi medium-entropy alloys.
• To investigate the in-situ evolution of SFE during tensile deformation.
• To correlate SFE variations with deformation mechanisms and determine critical twinning stresses.

Main Methods:

• Fabrication of AM SS 316L and CrCoNi specimens using directed energy deposition.
• In-situ neutron diffraction during room-temperature tensile loading to capture diffraction peaks from deformed grains.
• Analysis of peak profiles to calculate stacking fault probabilities and mean-square lattice strains, enabling SFE determination.
• Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) for microstructural and fault analysis.

Main Results:

• Averaged SFEs were 32.8 mJ/m² for AM SS 316L and 15.1 mJ/m² for AM CrCoNi.
• During deformation, SFE varied from 46 to 21 mJ/m² (SS 316L) and 24 to 11 mJ/m² (CrCoNi).
• Transient SFE changes were attributed to a transition from dislocation slip to twinning.
• Critical twinning stresses were determined as 830 ± 25 MPa for AM SS 316L and 790 ± 40 MPa for AM CrCoNi.

Conclusions:

• The study successfully quantified SFEs in AM SS 316L and CrCoNi alloys.
• Deformation-induced SFE variations are significant and linked to the onset of twinning.
• The determined critical twinning stresses provide valuable insights into the deformation mechanisms of these AM alloys.