Strain hardening engineering via grain size control in laser powder-bed fusion

Author(s)

Aota, Leonardo Shoji ; Souza Filho, Isnaldi R. ; Roscher, Moritz ; Ponge, Dirk ; Zschommler Sandim, Hugo Ricardo

• Document type: Journal article
• Source: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING; v. 838, p. 12-pg., 2022-03-24.

Abstract

The ultimate goal for structural materials is achieving both high strength and ductility. However, increasing one of these properties usually decrease the other, resulting in the so-called strength-ductility trade-off. According to the Conside`re criterion, increased strain hardening rates are demanded at higher strains to prevent necking and strain localization. This study reports a novel approach based on strain hardening engineering in a laser powder-bed fusion (LPBF) 304 L stainless steel deformed by tensile testing. The nucleation of alpha'-martensite directly from austenite (gamma) was observed without the formation of the intermediate e-phase. Both fine (11 mu m) and coarse (93 mu m) grains initially undergo dislocation slip and stacking fault formation in the as-built cellular structure up to a logarithmic strain (e) of 0.05. Fine austenite grains exhibit alpha'-martensite growing along the extended stacking fault bands (epsilon 110 parallel to LD (loading direction) oriented gamma-grains primarily accommodate the imposed macroscopic strain via twinning (0.2 > epsilon > 0.05), followed by martensitic transformation or activation of other twinning systems (epsilon > 0.2). Deformation twinning is hindered within fine grains due to a (1) higher twinning activation stress and (2) an unfavorable crystallographic orientation. The hierarchical defor-mation reported for 304 L stainless steel is crucial for component and alloy-for-LPBF design. This study reveals the possibility of using LPBF for strain hardening engineering through grain size control, triggering the hierar-chical deformation (and their interaction) in each grain family. As a result, high-strength and ductile alloys may be obtained by exploring this novel processing approach. (AU)

• FAPESP's process: 17/02485-2 - Characterization and evaluation of the microstructural stability of AISI 316L stainless steel processed via selective laser melting
• Grantee: Hugo Ricardo Zschommler Sandim
• Support Opportunities: Regular Research Grants
• FAPESP's process: 19/19442-0 - Microstructural stability of AISI 316L stainless steel processed by selective laser melting using different scanning strategies
• Grantee: Leonardo Shoji Aota
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• FAPESP's process: 18/23582-9 - Microstructural stability of 316L stainless steel processed via selective laser melting using different scanning strategies
• Grantee: Leonardo Shoji Aota
• Support Opportunities: Scholarships in Brazil - Master