Characterization of hydrogen embrittlement on novel low-Ni austenitic stainless steels & the investigation of ferroelastic domain mobility in barium titanate

Yurek, Quinten Bradley

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https://hdl.handle.net/2142/129362 Copy

Description

Title

Characterization of hydrogen embrittlement on novel low-Ni austenitic stainless steels & the investigation of ferroelastic domain mobility in barium titanate

Author(s)

Yurek, Quinten Bradley

Issue Date

2025-01-21

Director of Research (if dissertation) or Advisor (if thesis)

Krogstad, Jessica A

Doctoral Committee Chair(s)

Stubins, James F

Committee Member(s)

• Bellon, Pascal
• Charpagne, Marie
• Stinville, Jean-Charles

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Hydrogen Embrittlement
• Stainless Steel
• Low-Ni Steel
• Hydrogen Enhanced Localized Plasticity
• Barium Titanate
• Ferroelastic
• Ferroelasticity
• Micropillar
• Ferroelastic Micropillar Compression
• Pseudosymmetry
• Ferroelastic Domain Movement
• Domain Reorientation
• Coupled Ferroics

Abstract

Abstract for Work on Hydrogen Embrittlement in Novel Austenitic Stainless Steels This work is part of the DOE’s H2@Scale initiative and aims to provide low-Ni, cost-effective, and scalable austenitic stainless-steel alternatives to current commercial alloys, namely AISI 316 and Nitronic-40 (21-6-9). Furthermore, this study aims to advance the understanding of the relationship between alloy composition and bulk hydrogen embrittlement (HE) susceptibility through an investigation of hydrogen’s effect on deformation modes. Four novel low-Ni alloys (KU1-KU4) were designed with the following criteria: austenite stability, suppression of twinning-induced plasticity (TWIP), and cost reduction per kg. These alloys were then investigated alongside 316 and 21-6-9 in a hydrogen-saturated and no-hydrogen condition. This was done via tensile testing and employed a combination of pre-and post-deformation characterization methods including electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Bulk HE susceptibility was evaluated using total tensile elongation (TE), reduction of area (RA), and fracture surface morphology at room and low temperatures (-30°C). Transformation-induced plasticity (TRIP) was not observed in our alloy suite in the studied conditions indicating four novel low-Ni, stable austenitic stainless steels. At room temperature, KU1 and KU2 showed comparable HE resistance to 316 and 21-6-9 while exhibiting strength improvements and cost savings of at least 39%/kg relative to 316. KU4 was found to be a viable no-Ni replacement for 304L and provided the largest cost reduction and the highest strength. KU3 displayed unique hardening characteristics and moderate HE resistance but this alloy requires further optimization for improved yield strength and HE resistance. At low temperatures KU1 and KU2 both showed much higher HE susceptibility evidenced changes in fracture surface morphology and large reductions in RA. TEM analysis revealed hydrogen-induced slip localization and cross-slip restriction across all alloys at room temperature. The presence of Cu in KU2 was found to delay the onset of TWIP and enhance planar slip. KU4, due to its high Mn and hydrogen content experiences a transition from ductile to brittle intergranular failure. The influence of stacking fault energy (SFE) on deformation modes was found to be nuanced among our alloy suite and SFE has been found to be a poor predictor for TWIP in low-SFE alloys such as ours <40mJm2. This study advances our ability to provide a compositionally driven alloy design framework for HE-resistant compositions by linking composition to deformation modes. Additionally, this effort provides four novel low-Ni alloys for future study in the community and potential in commercial applications. Abstract for Work on Ferroelastic Domain Mobility Criteria in Tetragonal Barium Titanate This study aims to advance the fundamental understanding of ferroelasticity in tetragonal barium titanate (BT). This intrinsic toughening mechanism lacks well-defined domain mobility criteria, and we hypothesize that a Schmid-type resolved shear stress (RSS) criterion may be applicable to domain motion in ferroelastic systems. Furthermore, ferroelasticity may be isolated from other deformation mechanisms at elevated temperatures below the curie temperature (Tc). BT-based compounds are promising lead-free alternatives to the industry standard lead-zirconium titanate (PZT), thus understating domain mobility criteria in BT will serve as a corollary for BT-based compounds. Here we use large-grain, poly-domain tetragonal BT for micropillar compression experiments. These experiments are enabled by the material's large grain size and accessible Tc. Various independent micropillar arrays were fabricated and tested within six grains. Results showed no observable effects of loading rates between 70 µN/s and 700 µN/s on deformation behaviors. An inverse relationship between pillar size and failure, dislocation, and domain reorientation stresses was observed, with suppressed domain reorientation in smaller pillars due to reduced secondary domain boundaries and volumetric constraints. Temperature variations (20°C, 60°C, and 100°C) did not affect dislocation or domain reorientation stresses and internal microstructures were independent of temperature. The isolation of ferroelastic deformation at the tested temperatures was hindered by the competing deformation mechanisms of dislocation plasticity and microcracking. Stiffness tracking was employed to identify deformation mechanisms such as dislocation plasticity, domain switching, and microcracking, however, it could not be leveraged to provide information regarding fractional volumes of switched material within a pillar. Lastly, no correlation was found between domain reorientation normal or shear stress and Schmid factors for {110}<110> systems. This suggests that a critically resolved shear stress criterion for domain mobility in BT is not applicable. Our findings provide novel results around the size effect on deformation in BT and the suppression of domain reorientation in small-diameter pillars. Furthermore, this work advances knowledge in the field of domain dynamics in ferroelastic crystals. Specifically, how overlapping deformation mechanisms in micropillars make it difficult to isolate ferroelastic deformation. Challenges within this research space remain around isolating ferroelasticity and determining domain mobility criteria. Future work on poled single-domain BT or pseudo-binary BT-based compounds may yield different results by addressing current limitations and contributing to the development of lead-free piezoelectric materials for industrial applications.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129362

Copyright and License Information

Copyright 2025 Quinten Yurek

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