Athermal Martensite Transformation Curve

Rios, Paulo Rangel; Guimarães, J.R.C.

doi:10.1590/1980-5373-mr-2015-0690

Cited by 4 publications

(2 citation statements)

References 28 publications

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“…Martensite transition was first discovered in steels where it is irreversible and athermal [1]. In contrast, the temperatureand/or stress-induced martensite transitions in shape memory alloys (SMAs) like Ni-Ti [1][2][3]15,16], Ni-Al [1,17,18], and Cu-based alloys (like Cu-Zn-Al and Cu-Al-Ni) [2,19], and magnetic shape memory alloys (MSMAs) like Ni-Mn-Ga [20][21][22] are reversible and may have both athermal [1,[23][24][25] and isothermal [1,2,[24][25][26][27] characteristics, depending on the alloy system. The martensite transition is at the heart of the large and reversible shape change in the SMAs, wherein different orientational variants of the martensite phase, formed by twinning to maintain the invariant habit plane, merge on application of stress, while the original austenite state is recovered by heating to the austenite phase region [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Pair distribution function study ofNi2MnGamagnetic shape memory alloy: Evidence for the precursor state of the premartensite phase

Singh

Pandey

2021

Phys. Rev. B

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Precursor phenomena preceding the martensite phase transition play a critical role in understanding the important technological properties of shape memory and magnetic shape memory alloys (MSMAs). Since the premartensite phase of Ni 2 MnGa MSMA, earlier considered as the precursor state of the martensite phase, has in recent years been shown to be a thermodynamically stable phase, Singh et al. [Nat. Commun. 8, 1006(2017], there is a need to revisit the precursor effects in these materials. We present here evidence for the existence of a precursor state of the premartensite phase in Ni 2 MnGa MSMA by atomic pair distribution function analysis of high-energy, high-flux, and high-Q synchrotron x-ray powder diffraction data. It is shown that the local structure of the cubic austenite phase corresponds to the short-range ordered (SRO) precursor state of the 3M premartensite phase at temperatures well above the actual premartensite phase transition temperature T PM and even above the ferromagnetic (FM) transition temperature T C . The presence of such a SRO precursor state of the premartensite phase is shown to lead to significant volume strain, which scales quadratically with spontaneous magnetization. The experimentally observed first-order character of the paramagnetic-to-FM phase transition and the anomalous reduction in the value of the magnetization in the temperature range T PM < T < T C are explained in terms of the coupling of the magnetoelastic strain with the FM order parameter and the higher magnetocrystalline anisotropy of the precursor state of the premartensite phase, respectively.

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Section: Introductionmentioning

confidence: 99%

Pair distribution function study ofNi2MnGamagnetic shape memory alloy: Evidence for the precursor state of the premartensite phase

Singh

Pandey

2021

Phys. Rev. B

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“…This phase has recently been found within ringwoodite meteorites [126] due to fast coeval cooling and decompression right after the impact. In such materials, martensitic transformations can be induced by either changing the temperature (on cooling) or applying differential stress (e.g., [162,163]).…”

Section: The "Transformation": a Transient Metastable Phase Responsible For Enhanced Plasticity?mentioning

confidence: 99%

Reduced Viscosity of Mg2GeO4 with Minor MgGeO3 between 1000 and 1150 °C Suggests Solid-State Lubrication at the Lithosphere–Asthenosphere Boundary

Ferrand

Deldicque

2021

Minerals

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Tectonic plates are thought to move above the asthenosphere due to the presence of accumulated melts or volatiles that result in a low-viscosity layer, known as lithosphere–asthenosphere boundary (LAB). Here, we report experiments suggesting that the plates may slide through a solid-state mechanism. Ultrafine-grained aggregates of Mg2GeO4 and minor MgGeO3 were synthetized using spark plasma sintering (SPS) and deformed using a 1-atm deformation rig between 950 °C and 1250 °C. For 1000 < T < 1150 °C, the derivative of the stress–strain relation of the material drops down to zero once a critical stress as low as 30–100 MPa is reached. This viscosity reduction is followed by hardening. The deformation curves are consistent with what is commonly observed in steels during the shear-induced transformation from austenite to martensite, the final material being significantly harder. This is referred to as TRansformation-Induced Plasticity (TRIP), widely observed in metal alloys (TRIP alloys). It should be noted that such enhanced plasticity is not necessarily due to a phase transition, but could consist of any kind of transformation, including structural transformations. We suspect a stress-induced grain-boundary destabilization. This could be associated to the transient existence of a metastable phase forming in the vicinity of grain boundaries between 1000 and 1150 °C. However, no such phase can be observed in the recovered samples. Whatever its nature, the rheological transition seems to occur as a result of a competition between diffusional processes (i.e., thermally activated) and displacive processes (i.e., stress-induced and diffusionless). Consequently, the material would be harder at 1200 °C than at 1100 °C thanks to diffusion that would strengthen thermodynamically stable phases or grain-boundary structures. This alternative scenario for the LAB would not require volatiles. Instead, tectonic plates may slide on a layer in which the peridotite is constantly adjusting via a grain-boundary transformation.

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Thermal and Mechanical Stability of Austenite in Metastable Austenitic Stainless Steel

Tiamiyu

Zhao

et al. 2019

Metall Mater Trans A

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Athermal Martensite Transformation Curve

Cited by 4 publications

References 28 publications

Pair distribution function study ofNi2MnGamagnetic shape memory alloy: Evidence for the precursor state of the premartensite phase

Pair distribution function study ofNi2MnGamagnetic shape memory alloy: Evidence for the precursor state of the premartensite phase

Reduced Viscosity of Mg2GeO4 with Minor MgGeO3 between 1000 and 1150 °C Suggests Solid-State Lubrication at the Lithosphere–Asthenosphere Boundary

Thermal and Mechanical Stability of Austenite in Metastable Austenitic Stainless Steel

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