Correlation Between Microstructure and Mechanical Performance of an L-PBF 316L Alloy with an ISE-Free Parameter

Area of Science:

• Materials Science
• Mechanical Engineering
• Additive Manufacturing

Background:

• Accurate mechanical performance assessment of additive manufacturing (AM) products is crucial for optimization and engineering development.
• Standard Instrumented Indentation Test (IIT) methods lack procedures for materials with internal residual stress (RS).
• Nanoindentation testing is hindered by indentation size effects (ISE), complicating correlation of mechanical properties at different scales.

Purpose of the Study:

• To present a novel IIT methodology for non-destructive mechanical characterization of AM materials.
• To introduce new indentation parameters, loading stiffness rate (LSR) and rate-derived hardness (H_R), to overcome ISE and RS limitations.
• To validate the methodology by correlating results with microstructural analysis.

Main Methods:

• Implementation of a multiload/multiscale IIT strategy on an L-PBF 316L austenitic stainless-steel alloy.
• Introduction and application of new parameters: loading stiffness rate (LSR) and rate-derived hardness (H_R).
• Correlation of nanoindentation results with electron backscatter diffraction (EBSD) analysis.

Main Results:

• The novel LSR and H_R parameters exhibited ISE-free properties across nano- and macro-scales.
• The methodology successfully assigned mechanical performances, with obtained modulus (E_IT) slightly exceeding the reference Young's modulus.
• Loading secant stiffness versus depth plots indicated susceptibility of RS relaxation during indentation.
• Correlation between EBSD analysis (crystal anisotropy, grain size, dislocation density) and nanoindentation confirmed methodology validity.

Conclusions:

• The proposed IIT methodology, utilizing LSR and H_R, provides accurate and ISE-free mechanical property assessment for AM materials.
• The method aids in evaluating residual stress effects, crucial for engineering design of AM components.
• This work represents a significant step towards fully characterizing the process, properties, and performance (3Ps) of advanced AM products.