Martensitic and austenitic phase transformations in Fe–C nanowires

2019

Metals

Using molecular dynamics simulation, we studied the influence of pre-existing dislocations on the austenitic and the martensitic phase transformations in pure iron. The simulations were performed in a thin-film geometry with (100) surfaces. We found that dislocations alleviate the transformation by lowering the austenitic transformation temperature and increasing the martensitic transformation temperature. In all cases, the new phase nucleates at the dislocations. The orientation relationships governing the nucleation process are dominated by the Burgers, Kurdjumov–Sachs, and Nishiyama–Wassermann pathways. However, upon growth and coalescence of the transformed material, the final microstructure consists of only few twinned variants separated by twin boundaries; this simple structure is dictated by the free surfaces which tend to form conserved planes under the transformation. After transformation, the material also contains abundant dislocations.

Section: Introductionmentioning

confidence: 99%

Dislocations Help Initiate the α–γ Phase Transformation in Iron—An Atomistic Study

2019

Metals

“…In this study, we focus on cementite (Fe 3 C), and study the martensitic and austenitic transformations of an adjacent iron phase. Since previous studies demonstrated that the phase transformation behavior of Fe is only little influence by small alloying elements-such as C, Ni, or Cr [12][13][14][15]-the restriction to pure Fe appears justifiable.…”

Section: Introductionmentioning

confidence: 99%

Ferrite-to-Austenite and Austenite-to-Martensite Phase Transformations in the Vicinity of a Cementite Particle: A Molecular Dynamics Approach

2018

Metals

We used classical molecular dynamics simulation to study the ferrite–austenite phase transformation of iron in the vicinity of a phase boundary to cementite. When heating a ferrite–cementite bicrystal, we found that the austenitic transformation starts to nucleate at the phase boundary. Due to the variants nucleated, an extended poly-crystalline microstructure is established in the transformed phase. When cooling a high-temperature austenite–cementite bicrystal, the martensitic transformation is induced; the new phase again nucleates at the phase boundary obeying the Kurdjumov–Sachs orientation relations, resulting in a twinned microstructure.

“…Since they deliver an atomistic view on the processes occurring in the sample during the transformation, they may be used to help understand the experimental results. [6][7][8] MD simulations studied the martensitic transformation in pure iron [9][10][11][12][13][14][15][16] and iron alloys [17][18][19][20][21] ; bulk samples as well as thin films 22 and nanowires 23,24 were studied. The transformation process follows in these cases well-known orientation relationships.…”

mentioning

confidence: 99%

Martensitic transformation of pure iron at a grain boundary: Atomistic evidence for a two-step Kurdjumov-Sachs–Pitsch pathway

2016

AIP Advances

Self Cite

Using classical molecular dynamics simulations and the Meyer-Entel interaction potential, we study the martensitic transformation pathway in a pure iron bi-crystal containing a symmetric tilt grain boundary. Upon cooling the system from the austenitic phase, the transformation starts with the nucleation of the martensitic phase near the grain boundary in a plate-like arrangement. The Kurdjumov-Sachs orientation relations are fulfilled at the plates. During further cooling, the plates expand and merge. In contrast to the orientation relation in the plate structure, the complete transformation proceeds via the Pitsch pathway.