The effects of annealing treatment on mechanical properties of nanocrystalline α-iron: an atomistic study

• Author / Creator

  Tong, Xuhang

• Nanocrystalline metallic materials demonstrate superior mechanical, optical, and electric properties. Claims are often found in the literature that metallic materials can be nanocrystallized by severe plastic deformation (SPD). However, SPD does not generate a well-defined nanocrystalline material, which can be achieved by subsequent annealing/recovery treatment. In this study, molecular dynamics simulation is employed to investigate 1) the role of grain boundaries during deformation processes of nanocrystalline α-iron; 2) intrinsic effects of annealing treatment on mechanical properties of nanocrystalline α-iron. Investigations of the structures and deformation behaviors have demonstrated that local structure and local stress at grain boundary areas determine the overall mechanical properties of nanocrystalline. To simulate nanocrystalline α-iron generated by SPD process, we built a polycrystalline system and applied cyclic load to the system to generate abundant internal defects. The simulation demonstrates that grain boundary in the deformed NC α-iron evolve to a more equilibrium state, eliminating or minimizing the residual stress during annealing treatment. The annealing treatment increases the system’s strength by reducing dislocation emission sources, and improves materials ductility through strengthening grain boundaries’ resistance to intergranular cracks. The results indicate that the annealing treatment is an essential process for obtaining a well-defined NC structure with superior mechanical properties.

• Subjects / Keywords

  • Annealing treatment
  • Molecular-dynamics
  • Nanocrystalline
  • Α-iron
  • Grain boundary

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ZK55S15

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.