Characterization of Residual Stress Evolved in Iron-Based Shape Memory Alloys*
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S. Suzuki
Abstract
It is considered that complicated residual stresses may occur in shape memory alloys (SMAs) during deformation, as the matrix phase is transformed to martensitic phase during plastic deformation and the martensitic phase is reversely transformed by heating. Since the final shape of SMAs are influenced by residual stresses, it is important to characterize the residual stresses formed in SMAs during plastic deformation and annealing. The X-ray diffraction method was used to characterize the phase transformation and the residual stress formed in an Fe-Mn-Si-Cr SMA in this study. The samples were tensile-deformed to different strains and subsequently annealed. The results showed that a part of γ-phase with the face-centered cubic (fcc) structure was found to be transformed to ∊-phase with the hexagonal close-packed (hcp) structure by room-temperature tensile deformation in the SMA, and the ∊-phase was reversely transformed by subsequent heating. It has been also shown that the compressive stress occurred in the tensile direction of the γ-phase on tensile deformation and unloading. The compressive stress is believed to result from the formation of the ∊-phase during stress-induced martensitic transformation. After the deformed samples were annealed to recover their shapes, the residual stress was considerably released. This is considered to be due to the decrease in the amount of the transformed ∊-phase during annealing. These results indicated that residual stress in the fcc matrix phase is correlated with the shape recovery characteristics of the SMA after martensitic and reverse martensitic transformations.
Kurzfassung
Es wird angenommen, dass Form-Gedächtnis-Legierungen während der Formänderungen (FGL), die durch Phasenumwandlung zu Martensit bei plastischer Verformung und zurück zu Austenit bei Erwärmung gekennzeichnet sind, komplizierte Eigenspannungszustände durchlaufen. Da die Endform der Formänderungen von den Eigenspannungen bestimmt wird, ist eine Charakterisierung der Eigenspannungszustände während plastischer Verformung und Erwärmung notwendig. Für die vorliegende Untersuchung wurden die Eigenspannungen sowie Phasenumwandlungen einer Fe-Mn-Si-Cr-FGL mit Röntgendiffraktometrie gemessen. Die Proben wurden zu verschiedenen Umformgraden gezogen und anschließend erwärmt. Die Messungen ergeben, dass ein Teil der γ-Phase mit kubisch-flächenzentrierter (fcc) Struktur durch plastische Deformation bei Raumtemperatur in eine ∊-Phase mit hexagonal-dichtester Packung (hcp) umgewandelt wird, welche durch Erwärmung wieder zurück umgewandelt wird. Es konnte ebenfalls gezeigt werden, dass während der Zugverformung und der anschließenden Entlastung Druckeigenspannungen in Zugrichtung innerhalb der γ-Phase auftreten. Diese werden auf die Bildung der ∊-Phase während der spannungsinduzierten Martensitumwandlung zurückgeführt. Nachdem die verformten Proben erwärmt wurden, um ihre ursprüngliche Form wiederherzustellen, hatten sich die Eigenspannungen deutlich abgebaut. Dies lässt sich durch den Abbau der ∊-Phase während des Glühens erklären. Diese Ergebnisse legen nahe, dass der Form-Gedächtnis-Effekt der FLG durch die Eigenspannungen in der kubisch-flächenzentrierten Matrix während der martensitischen und invers-martensitischen Umwandlung erzeugt wird.
References
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Articles in the same Issue
- Veranstaltungen/Events
- Veranstaltungen in Zusammenarbeit mit der AWT
- HTM-Praxis
- HTM-Praxis
- Kurzfassungen/Abstracts
- Kurzfassungen
- Inhalt/Contents
- Inhalt
- Fachbeiträge/Technical Contributions
- Preface
- Residual Stress in the Cementite Phase of Cold Drawn Pearlite*
- Residual Stress Analysis of Thick Film Systems by the Incremental Hole-Drilling Method*
- Stress Build-Up during Multilayer Welding with Novel Martensitic Filler Materials*
- Characterization of Residual Stress Evolved in Iron-Based Shape Memory Alloys*
- Microstructure and Properties of Pearlitic Steel during Cold Wire Drawing: A Residual Stress Perspective*
- Shot Peening Induced Plastic Deformation in Cast Iron – Influence of Graphite Morphology*
- Heat Treatment Effects of Laser Cladded 12 Ni Maraging Tool Steel with Ni-Co-Mo Alloys*
