An extraordinary-performance gradient nanostructured Hadfield manganese steel containing multi-phase nanocrystalline-amorphous core-shell surface layer by laser surface processing

Wanting Sun, Jiasi Luo, Yim Ying Chan, J. H. Luan, Xu Sheng Yang

Research output: Journal article publicationJournal articleAcademic researchpeer-review

15 Citations (Scopus)

Abstract

Reducing grain size (i.e. increasing the fraction of grain boundaries) could effectively strengthen nanograined metals but inevitably sacrifices the ductility and possibly causes a strengthening-softening transition below a critical grain size. In this work, a facile laser surface remelting-based technique was employed and optimized to fabricate a ∼600 μm-thick heterogeneous gradient nanostructured layer on an austenitic Hadfield manganese steel, in which the average grain size is gradually decreased from ∼200 μm in the matrix to only ∼8 nm in the nanocrystalline-amorphous core-shell topmost surface. Atomic-scale microstructural characterizations dissected the gradient refinement processes along the gradient direction, i.e. transiting from the dislocations activities and twinning in sub-region to three kinds of martensitic transformations, and finally a multi-phase nanocrystalline-amorphous core-shell structural surface. Mechanical tests (e.g. nanoindentation, bulk-specimen tensile, and micro-pillar compression) were conducted along the gradient direction. It confirms a tensile strength of ∼1055 MPa and ductility of ∼10.5% in the laser-processed specimen. Particularly, the core-shell structural surface maintains ultra-strong (tensile strength of ∼1.6 GPa, micro-pillar compressive strength of ∼4 GPa at a strain of ∼8%, and nanoindentation hardness of ∼7.7 GPa) to overcome the potential strengthening-softening transition. Such significant strengthening effects are ascribed to the strength-ductility synergetic effects-induced extra work hardening ability in gradient nanostructure and the well-maintained dislocation activities inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface, which are evidenced by atomic-scale observations and theoretical analysis. This study provides a unique hetero-nanostructure through a facile laser-related technique for extraordinary mechanical performance.

Original languageEnglish
Pages (from-to)209-222
Number of pages14
JournalJournal of Materials Science and Technology
Volume134
DOIs
Publication statusPublished - 20 Jan 2023

Keywords

  • Gradient nanostructure
  • Hadfield manganese steel
  • Laser surface processing
  • Martensitic transformation
  • Nanocrystalline-amorphous

ASJC Scopus subject areas

  • Ceramics and Composites
  • Mechanics of Materials
  • Mechanical Engineering
  • Polymers and Plastics
  • Metals and Alloys
  • Materials Chemistry

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