The Character Of Martencitic Transformation And Shape Memory Effect In Fe-Mn-Si-Cr-Ni-N Alloy

Martensite morphology, macroscopic lattice deformation and shape memory effect(SME) in Fe-25.27Mn-5.54Si-6.89Cr-5.06Ni-0.16N alloy were studied by tensile testing machine ,X-ray, Scanning Electron Microscope(SEM) , Transmission Electron Microscope(TEM), Atomic Force Microscope(AFM) and so on. The relationship between SME and microscopic structure was revealed. The factors on SEM about morphology and crystallography were also investigated.The results show that morphology and content of martensite changed with pre-strain. γ→ s martensitic transformation occurred after 1% pre-strain and e martensite with 20.0% volume were distributed in parallel pattern. The pattern changed to rhombus self-accommodate after 4% pre-strain and the volume became to 50.4%. While, the pattern changed to intersection and α' martensite appeared after 6% pre-strain, then, the volume of α' martensite was 18.9% and e martensite was 43.8%. When the pre-strain increased to 9%, the volume of ε martensite was 22.0% and more intersecting e martensite appeared, then, the volume of α' martensite increased to 54.3%.The results of shape memory effect show that the recovery ratio descended with pre-strain. The recovery ratio was 56.3%,50.2%,42.5%,35.7%, respectively, with 1%,4%,6%,9% pre-strain. While, SME could improve by thermomechanical training method. The recovery ratio was 63.5%,59.3%,57.2%,43.2%, respectively, after 2 circle training. The reasons for recovery ratio descent were ￡ martensite intersection and α' martensite appearance,ε martensite could rearrange after appropriate training method so that the recovery ratio was improved.The macroscopic lattice deformation was analyzed by AFM. The results show that surface relief morphology had relations with pre-strain. The stress-induced surface relief is "N"-shaped including parallel and intersecting arrangement. The height of parallel surface relief increased with pre-strain. Then, the width of parallel surface relief decent after 6% pre-strain. The intersecting surface relief appeared after 6% pre-strain. While, the height, width, angle was feebler than parallel surface relief, respectively. The inverse deformation ratio was very low after 873 ×120s h1eating. The test alloy could get better shape recovery ratio when the surface reliefwas parallel arrangement. While,the recovery ratio descended when the surface relief was intersection, which inhibited reverse transformation.The SME was infected with martensite morphology and macroscopic lattice deformation. The higher shape recovery ratio could be obtained when martensite morphology and surface relief parallel arranged. While,the higher shape recovery ratio could be obtained when martensite morphology and surface relief intersecting arranged. Then, the lattice arrangement would be confused and the shape recovery ratio would decrease.