Grain size effect on the structural parameters of the stress induced epsilonhcp: martensite in iron-based shape memory alloy

Nascimento, Fabiana Cristina; Mei, Paulo Roberto; Cardoso, Lisandro Pavie; Otubo, Jorge

doi:10.1590/s1516-14392008000100012

Cited by 9 publications

(3 citation statements)

References 23 publications

(42 reference statements)

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“…Although in a small quantity, some monovariant martensite plates were observed within the finer grains region. However, according to previous works 13,26 , the decrease in the grain size would improve shape recovery owing to the shape memory effect and, therefore, a pronounced monovariant γ to ε phase transformation at the small grain sizes region was expected, but this did not happen. This behaviour could be explained considering that the γ → ε martensitic transformation presents a positive volume variation.…”

Section: Microstructural Evolutionmentioning

confidence: 77%

The Influence of Microstructure and Mechanical Resistance on the Shape Memory of Ecae Processed Stainless Fe-Mn-Si-Cr-Ni-Co Steel

Käfer

Bernardi²,

Santos

et al. 2018

Mat. Res.

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In the current work, XRD, SEM, EBSD and TEM techniques were used to evaluate the microstructure of stainless Fe-Mn-Si-Cr-Ni-Co shape memory steel processed by ECAE and annealed for one hour at temperatures ranging from 650ºC to 950ºC. The results were then correlated with the mechanical and shape-memory properties of the steel. It was observed that the samples containing large grains and a microstructure free of defects or precipitates presented a high volume fraction of multi-variant thermal martensite and stress-induced martensite, resulting in good shape recovery, owing to the memory effect. The grain refinement and precipitation of second-phase particles decreased the volume fraction and number of martensite variants and considerably increased the mechanical resistance, enhancing the elastic shape recovery. It was shown that shape memory properties were essentially related to the mechanical resistance of the matrix, which in turn was related to the microstructure.

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Section: Microstructural Evolutionmentioning

confidence: 77%

The Influence of Microstructure and Mechanical Resistance on the Shape Memory of Ecae Processed Stainless Fe-Mn-Si-Cr-Ni-Co Steel

Käfer

Bernardi²,

Santos

et al. 2018

Mat. Res.

Self Cite

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“…However, the magnitude of ΔV represents the reversibility of the martensitic transformation and is important for shape memory effect 32 . And, while martensite reversibility was predicted from changes in c/a ratio previously 33 , transformation volume is a more appropriate measure of reversibility 22 . Lower |ΔV| corresponds to higher reversibility and shape memory effect.…”

Section: Resultsmentioning

confidence: 99%

On the evolving nature of c/a ratio in a hexagonal close-packed epsilon martensite phase in transformative high entropy alloys

Sinha

Nene

Frank

et al. 2019

Sci Rep

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Activation of different slip systems in hexagonal close packed (h.c.p.) metals depends primarily on the c/a ratio, which is an intrinsic property that can be altered through alloying addition. In conventional h.c.p. alloys where there is no diffusion-less phase transformation and associated transformation volume change with deformation, the c/a ratio remains constant during deformation. In the present study, c/a ratio and transformation volume change of h.c.p. epsilon martensite phase in transformative high entropy alloys (HEAs) were quantified as functions of alloy chemistry, friction stir processing and tensile deformation. The study revealed that while intrinsic c/a is dependent on alloying elements, c/a of epsilon in transformative HEAs changes with processing and deformation. This is attributed to transformation volume change induced dependence of h.c.p. lattice parameters on microstructure and stress state. Lower than ideal c/a ratio promotes non-basal pyramidal 〈c + a〉 slip and deformation twinning in epsilon phase of transformative HEAs. Also, a unique twin-bridging mechanism was observed, which provided experimental evidence supporting existing theoretical predictions; i.e., geometrical factors combined with grain orientation, c/a ratio and plastic deformation can result in characteristic twin boundary inclination at 45–50°.

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“…In 1990, Otsuka et al further developed stainless Fe – Mn – Si–Cr–(Ni) SMAs, such as Fe–28Mn–6Si–5Cr, Fe–20Mn–5Si–8Cr–5Ni, and Fe–16Mn–5Si–12Cr–5Ni . Furthermore, effects of other alloying elements such as interstitial atoms, rare earth elements, copper, and cobalt on SME were investigated in the Fe – Mn – Si‐based SMAs. In addition to the SME, a lot of researches on factors influencing the recovery stress of Fe – Mn – Si‐based SMAs have also been done .…”

Section: Role Of Si In Achieving Large Recovery Strains In Fe–mn–si‐bmentioning

confidence: 99%

Key Factors Achieving Large Recovery Strains in Polycrystalline Fe–Mn–Si‐Based Shape Memory Alloys: A Review

et al. 2017

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Fe-Mn-Si-based shape memory alloys are the most favorable for largescale applications owing to low cost, good workability, good machinability, and good weldability. However, polycrystalline Fe-Mn-Si-based shape memory alloys have low recovery strains of only 2-3% after solution treatment, although monocrystalline ones reach a large recovery strain of %9%. This review gives an overview of the improvement of recovery strains for polycrystalline Fe-Mn-Si-based shape memory alloys. It is proposed that two fundamental aspects, that is, composition design and microstructure design, shall be satisfied for obtaining large recovery strains of above 6%. Alloying compositions determining the ceiling of recovery strains shall follow three guidelines: (i) Si content is 5-6 wt%; (ii) 20 wt% Mn 32 wt%; (iii) addition of elements strongly strengthening austenite matrix. Microstructure design includes coarsening austenitic grains and reducing twin boundaries as far as possible together with introducing a high density of stacking faults and second phases of strengthening austenite.

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Grain size effect on the structural parameters of the stress induced epsilonhcp: martensite in iron-based shape memory alloy

Cited by 9 publications

References 23 publications

The Influence of Microstructure and Mechanical Resistance on the Shape Memory of Ecae Processed Stainless Fe-Mn-Si-Cr-Ni-Co Steel

The Influence of Microstructure and Mechanical Resistance on the Shape Memory of Ecae Processed Stainless Fe-Mn-Si-Cr-Ni-Co Steel

On the evolving nature of c/a ratio in a hexagonal close-packed epsilon martensite phase in transformative high entropy alloys

Key Factors Achieving Large Recovery Strains in Polycrystalline Fe–Mn–Si‐Based Shape Memory Alloys: A Review

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