Structural Characterization of Stress-Induced Martensitic Transformation in a Polycrystalline Austenitic Fe-Mn-Si-Cr Alloy

Abstract

Stress-induced martensitic transformation in Fe-Mn-Si alloys is characterized by the transformation of the fcc matrix to the hcp phase, which is generally reversible. In this study, Debye rings obtained by monochromated X-ray diffraction using synchrotron radiation were used for analyzing the structural change of the fcc matrix to the hcp phase in a polycrystalline austenitic Fe-Mn-Si-Cr alloy that was deformed by the tensile test at room temperature. Structural changes resulting from the reverse transformation due to heating were also studied. The results showed that the occurrence of the stress-induced martensitic transformation was not uniform, but depended on the relationship between the orientation of polycrystalline grains and the tensile direction. The transformation appears to preferentially occur in grains with large Schmid factors for the shear of [ 2 211](111) in the fcc matrix, and the formation of hcp phases also depends on the orientation of grains. The reverse transformation due to heating does not necessarily occur in the crystallographically reversible route. This indicates that irreversible deformation induced by dislocations during the tensile test restricts the reversible transformation of the alloy.

Achievements and Perspectives on Fe-Based Shape Memory Alloys for Rehabilitation of Reinforced Concrete Bridges: An Overview

“…When the unidirectional austenite of the alloy is subjected to shear stress, the Shockley partial dislocation moves in the most favorable direction which promotes the growth of a single type of martensite. The ε martensite with the preferred orientation undergoes a huge shearing deformation, resulting in a significant change in the shape of the alloy [78]. At this time, heating the alloy to above A f can activate the reverse transformation (γ → ε), and the Shockley partial dislocations move in the opposite direction to martensite transformation (see Figure 4c).…”

A Novel Training-Free Processed Fe-Mn-Si-Cr-Ni Shape Memory Alloy Undergoing δ → γ Phase Transformation

“…After being subsequently annealed at 873 K (600°C), the alloy's shape recovery ratio further increased to 90 pct due to the reduction in the dislocations, which inhibit the stress-induced e-martensitic transformation. [13,[37][38][39] On the contrary, after being subsequently annealed at 1373 K (1100°C), the alloy's shape recovery ratio decreased to 76 pct because of the reduction in the amount of stacking faults, which are beneficial to stress-induced e-martensitic transformation. [5] For solution-treated alloy after heating at 1523 K (1250°C) and air cooling, a high density of twin boundaries, which has a negative effect on the shape memory effect, still existed ( Figure 3).…”

Characteristic Evolution of Residual Stress in Shape Memory Fe-Mn-Si-Cr Alloys

“…When plastically deformed SMAs are annealed over temperatures of about 600 K, the ε−γ reverse transformation occurs. Although the shape-recovering abilities of SMAs are due to the reverse martensitic transformation, they are significantly affected by the polycrystalline microstructure and texture of SMAs during stress-induced martensitic and reverse martensitic transformations [3,4]. As the overall shape recovery characteristics of SMAs may also be affected by the mechanical residual stresses in them, it is of great importance to be able to characterize the evolution of residual stresses in polycrystalline SMAs during deformation and annealing.…”