Subgrain lath martensite mechanics: A numerical–experimental analysis

Maresca, Francesco; Kouznetsova, V Varvara; Geers, Mgd Marc

doi:10.1016/j.jmps.2014.09.002

Cited by 54 publications

(46 citation statements)

References 45 publications

(101 reference statements)

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“…This austenite is thus stabilized and retained at room temperature. The RA phase is often under the form of very thin films (<0.1 lm) located along the martensite lath boundaries [28]. The second concept involves only a quenching followed by inter-critical tempering.…”

Section: Bulk Ultrafine Grained and Nanocrystalline Metalsmentioning

confidence: 99%

“…For instance, the effect of thin films of austenite located along lath or grain boundaries in ferrous lath martensite (Fig 2c) must be distinguished from the dual phase effect observed in duplex UFG steels. The recent studies by Mine et al [124] and Maresca et al [28] provide a detailed analysis of the deformation modes of the tiny austenite films. Slip transfer from one phase to the other one depends on the crystallography and the orientation relationship.…”

Section: Deformation Mechanisms In Nc and Ufg Multiphased Metalsmentioning

confidence: 99%

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Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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a b s t r a c tPushing the internal or external dimensions of metallic alloys down to the nanometer scale gives rise to strong materials, though most often at the expense of a low ductility and a low resistance to cracking, with negative impact on the transfer to engineering applications. These characteristics are observed, with some exceptions, in bulk ultra-fine grained and nanocrystalline metals, nano-twinned metals, thin metallic coatings on substrates and freestanding thin metallic films and nanowires. This overview encompasses all these systems to reveal commonalities in the origins of the lack of ductility and fracture resistance, in factors governing fatigue resistance, and in ways to improve properties. After surveying the various processing methods and key deformation mechanisms, we systematically address the current state of the art in terms of plastic localization, damage, static and fatigue cracking, for three classes of systems: (1) bulk ultra-fine grained and nanocrystalline metals, (2) thin metallic films on substrates, and (3) 1D and 2D freestanding micro and nanoscale systems. In doing so, we aim to favour cross-fertilization between progress made in the fields of mechanics of thin films, nanomechanics, fundamental researches in bulk nanocrystalline metals and metallurgy to impart enhanced resistance to fracture and fatigue in high-strength nanostructured systems. This involves exploiting intrinsic mechanisms, e.g. to enhance hardening and rate-sensitivity so as to delay necking, or improve grain-boundary cohesion to resist intergranular cracks or voids. Extrinsic methods can also be utilized such as by hybridizing the metal with another material to delocalize the deformation -as practiced in stretchable electronics. Fatigue crack initiation is in principle improved by a fine structure, but at the expense of larger fatigue crack growth rates. Extrinsic toughening through hybridization allows arresting or bridging cracks. The content and discussions are based on experimental, theoretical and simulation results from the recent literature, and focus is laid on linking microstructure and physical mechanisms to the overall mechanical behavior.

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Section: Bulk Ultrafine Grained and Nanocrystalline Metalsmentioning

confidence: 99%

Section: Deformation Mechanisms In Nc and Ufg Multiphased Metalsmentioning

confidence: 99%

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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“…This observation can have important consequences for the mechanical response. Maresca et al [12] suggest that even a small fraction of interlath RA can enhance the deformation of microstructures based on lath martensite.…”

Section: Introductionmentioning

confidence: 99%

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Hidalgo

Santofimia

2016

Metall Mater Trans A

177

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Current trends in steels are focusing on refined martensitic microstructures to obtain high strength and toughness. An interesting manner to reduce the size of martensitic substructure is by reducing the size of the prior austenite grain (PAG). This work analyzes the effect of PAGS refinement by thermal cycling on different microstructural features of as-quenched lath martensite in a 0.3C-1.6Si-3.5Mn (wt pct) steel. The application of thermal cycling is found to lead to a refinement of the martensitic microstructures and to an increase of the density of high misorientation angle boundaries after quenching; these are commonly discussed to be key structural parameters affecting strength. Moreover, results show that as the PAGS is reduced, the volume fraction of retained austenite increases, carbides are refined and the concentration of carbon in solid solution as well as the dislocation density in martensite increase. All these microstructural modifications are related with the manner in which martensite forms from different prior austenite conditions, influenced by the PAGS.

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“…The resolved shear stresses of the in-habit-plane and out-of-habit-plane slip systems were 285 and 360 MPa, respectively, and the ratio of the latter to the former was 1.3, similar to the 1.5 ratio of lath martensite. It is suspected that the difference in resolved shear stress between the inhabit-plane and out-of-habit-plane slip systems is caused by the existence of retained austenite between laths, as Maresca claims, 24) carbides included in the matrix, or block boundaries. These results revealed that both bainite and martensite show habit-plane-orientation-dependent yielding.…”

Section: Micro-tensile Behaviour In Bainitementioning

confidence: 99%

Micro-tensile Behaviour of Low-alloy Steel with Bainite/martensite Microstructure

et al. 2016

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Micro-tensile testing and numerical analysis using a crystal plasticity finite element method (CPFEM) were employed to elucidate the deformation behaviour of bainite/martensite structures of a low-alloy steel. The bainite single-phase specimens exhibited habit-plane-orientation-dependent yielding, similar to the martensite single-phase specimens. In the bainite/martensite dual-phase specimen, deformation concentrated in the bainite region oriented favourably for in-habit-plane slip, leading to low-ductility fracture. With consideration of the habit-plane-orientation-dependent yielding, the present CPFEM analysis successfully reproduced the anisotropic plastic deformation behaviour of the single-phase steels observed in the experiments. The numerical results for the bainite/martensite specimen showed slip localization in the bainite region and stress concentration near the interphase boundary. This suggests that the interphase boundary can be a site for the fracture origin.KEY WORDS: micromechanical characterisation; bainite; martensite-austenite constituent; crystal plasticity finite element analysis; plastic anisotropy; habit plane.tensitic phases hinders the understanding of the mechanical response of each phase.Mine et al. have analysed the mechanical characteristics of the microconstituents in the single-phase lath martensite structure of a low-alloy steel using micro-tensile testing.12) This study revealed that lath martensite structures with single packets exhibited moderate ductility and that the plastic deformation behaviour depended on the habitplane orientation relative to the loading direction. Thus, micro-tensile testing allows for the analysis of deformation behaviour on the microstructural scale. In addition, a microtensile test study by Ogata et al. indicated that pre-strained ferrite/martensite dual-phase steel was embrittled by ultra grain refinement in the ferrite region, rather than by cracking in the martensite region.13) This finding suggested that martensite was not always the main cause of embrittlement in high-strength steels. In the present study, microtensile testing was employed to characterise the mechanical response of each phase in a bainite/martensite structure. Additionally, numerical analysis with crystal plasticity finite element method (CPFEM) was performed to elucidate the microscopic mechanism of the experimentally observed deformation behaviour.The CPFEM analyses have helped in understanding plastic behaviours, 14,15) and studies on dual-phase steels successfully reproduced the observed deformation and fracture behaviours. 16,17) However, few studies have applied CPFEM to bainite/martensite dual-phase-structured steel. Therefore, in the present study, we confirm the applicability of a simple CPFEM with linear hardening laws to the deforma- ISIJ International, Vol. 56 (2016), No. 12tion behaviour of the bainite and martensite single-phase structures. Furthermore, by using the material parameters identified in the analyses of single-phase structures, the analysis of the bainit...

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Subgrain lath martensite mechanics: A numerical–experimental analysis

Cited by 54 publications

References 45 publications

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Micro-tensile Behaviour of Low-alloy Steel with Bainite/martensite Microstructure

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