Incubation times and entropy barriers in martensitic kinetics: Monte Carlo quench simulations of strain pseudospins

Shankaraiah, N.; Murthy, K. P. N.; Lookman, Turab; Shenoy, Subodh R.

doi:10.1209/0295-5075/92/36002

Cited by 16 publications

(64 citation statements)

References 29 publications

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“…Finally, considering that β and γ can be calculated with Eqs. (6)(7) and N VM obtained directly from the microstructure, the number density of the initial nucleation sites can be determined (8) …”

Section: Methodsmentioning

confidence: 99%

“…The transformation is heterogeneous and initiates at scarce austenite sites 3 where thermal atomic mobility is somehow inhibited as discussed in 4 . The development of multi-variant nuclei therein yields the transformation 5,6 . Martensite propagates rapidly 7,8 , however, its displacive character prevents martensite crossing high-angle boundaries.…”

Section: Introductionmentioning

confidence: 99%

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Martensite Transformation Intergrain and Intragrain Autocatalysis in Fe-Ni alloys

Guimarães

Rios

2017

Mat. Res.

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This work presents a consolidated view of the autocatalysis, thermal and entropic effects in martensitic transformation of polycrystalline Fe-31wt%Ni-0.02wt%C, which has been a standard material for the investigation of fundamental aspects of the martensite transformation. The present work is based on the description of classical microstructure descriptors of the transformation and on generally accepted concepts regarding the martensitic transformation in iron base alloys. Present work agrees with the view that the autocatalysis is a means by which the martensite transformation promotes further nucleation and growth. Autocatalysis induces the nucleation and growth of secondary plates in addition to the relatively small number of primary nucleation sites and their corresponding primary plates. We demonstrate that autocatalysis can be factored out into intragrain and intergrain components. The analysis of these factors establishes that intragrain autocatalysis is athermal but intergrain autocatalysis possess an Arrhenius temperature dependence. The reasons for such a behavior are discussed in detail.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Martensite Transformation Intergrain and Intragrain Autocatalysis in Fe-Ni alloys

Guimarães

Rios

2017

Mat. Res.

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“…Since atomic mobility in the austenite opposes the existence of highly correlated atomic clusters, entropic barriers exist that delimit initiation of the martensite transformation [14][15][16] . Consequently, martensite nucleation occurs heterogeneously at sites where the atomic displacements are somehow limited 15 , thus requiring the appearance of transformation-embryos, e.g., existence of lattice faults 17 .…”

Section: Formalismmentioning

confidence: 99%

“…Comparing, α X ≈ 1 should reflect a less intense feedback from the relaxation of the transformation strains. We propose that α X ≈ 1 stems from stress-accommodating micro-domains within the martensite unit 14,39,42 as well as from slip during the motion of the martensite-austenite interface [43][44][45] .…”

Section: The Autocatalytic Pathmentioning

confidence: 99%

Autocatalysis, Entropic Aspects and the Martensite Transformation Curve in Iron-Base Alloys

Guimarães

Rios

2017

Mat. Res.

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This study advances a methodology that consolidates the description of time-dependent (isothermal) as well as time-independent (athermal) martensitic transformation curves. Our model is applied in an extended 3-space, thus permitting inclusion of the effects of autocatalysis on nucleation to be distinguished from the initiation of the transformation, as influenced by entropic barriers. Autocatalysis is then considered as a mechanism for circumventing the effect of the latter. The utility of this proposed mathematical formalism was validated with a database consisting of seven different steels that transform athermally or isothermally.

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“…The microstructures generated from these strain-pseudospin models using local mean-field approximation 13 are in good agreement with the continuous variable models [5][6][7] and experiments 10 . Systematic temperature-quench MC simulations were performed on the simplest scalar-OP, 3-state pseudospin Hamiltonian for square-to-rectangle (SR) transition 14 and showed both rapid conversions below a spinodallike temperature and incubation-delays above it, as in experiments 4 on athermal martensitic materials. The conversion-time delays found to have Vogel-Fulcher divergences, which are insensitive to Hamiltonian energy scales and log-normal distributions, suggesting the dominant role of entropy barriers.…”

Section: Introductionmentioning

confidence: 95%

Monte Carlo simulations of vector pseudospins for strains: Microstructures and martensitic conversion times

Shankaraiah

2016

Journal of Alloys and Compounds

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We present systematic temperature-quench Monte Carlo simulations on discrete-strain pseudospin model Hamiltonians to study microstructural evolutions in 2D ferroelastic transitions with twocomponent vector order parameters (NOP = 2). The zero value pseudospin is the single hightemperature phase while the low-temperature phase has Nv variants. Thus the number of nonzero values of pseudospin are triangle-to-centered rectangle (Nv = 3), square-to-oblique (Nv = 4) and triangle-to-oblique (Nv = 6). The model Hamiltonians contain a transition-specific Landau energy term, a domain wall cost or Ginzburg term, and power-law anisotropic interaction potential, induced from a strain compatibility condition. On quenching below a transition temperature, we find behaviour similar to the previously studied square-to-rectangle transition (NOP = 1, Nv = 2), showing that the rich behaviour found, is generic. Thus we find for two-component order parameters, that the same Hamiltonian can describe both athermal and isothermal martensite regimes for different material parameters. The athermal/isothermal/austenite parameter regimes and temperature-timetransformation diagrams are understood, as previously, through parametrization of effective-droplet energies. In the athermal regime, we find rapid conversions below a spinodal like temperature and austenite-martensite conversion delays above it, as in the experiment. The delays show early incubation behaviour, and at the transition to austenite the delay times have Vogel-Fulcher divergences and are insensitive to Hamiltonian energy scales, suggesting that entropy barriers are dominant.

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Incubation times and entropy barriers in martensitic kinetics: Monte Carlo quench simulations of strain pseudospins

Abstract: PACS 64.70.K--Solid-solid transitions PACS 64.60.De -Statistical mechanics of model systems (Ising model, Potts model, field-theory models, Monte Carlo techniques, etc.

Cited by 16 publications

References 29 publications

Martensite Transformation Intergrain and Intragrain Autocatalysis in Fe-Ni alloys

Martensite Transformation Intergrain and Intragrain Autocatalysis in Fe-Ni alloys

Autocatalysis, Entropic Aspects and the Martensite Transformation Curve in Iron-Base Alloys

Monte Carlo simulations of vector pseudospins for strains: Microstructures and martensitic conversion times

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