The morphology of lath martensite: a new perspective

Koumatos, Konstantinos; Muehlemann, Anton

doi:10.1051/matecconf/20153307003

Cited by 5 publications

(3 citation statements)

References 18 publications

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“…In the present article, we extend upon previous results in [KM15] and build double shear theories to describe the deformation in a single lath by choosing both shearing systems as those which are macroscopically equivalent to twinning. Based on this assumption, we are able to build a model that predicts double shear theories with certain {h h k} γ habit planes as those satisfying a condition of low shape strain magnitude and maximal compatibility.…”

Section: Introductionmentioning

confidence: 83%

A parameter-free double-shear theory for lath martensite

Koumatos

Muehlemann

2019

Acta Cryst Sect A

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A double‐shear theory is introduced that predicts the commonly observed {5 5 7}γ habit planes in low‐carbon steels. The novelty of this theory is that the shearing systems are chosen in analogy to the original (single‐shear) phenomenological theory of martensite crystallography as those that are macroscopically equivalent to twinning. Out of all the resulting double‐shear theories, the ones leading to certain {h h k}γ habit planes naturally arise as those having small shape strain magnitude and satisfying a condition of maximal compatibility, thus making any parameter fitting unnecessary. An interesting finding is that the precise coordinates of the predicted {h h k}γ habit planes depend sensitively on the lattice parameters of the face‐centered cubic (f.c.c.) and body‐centered cubic (b.c.c.) phases. Nonetheless, for various realistic lattice parameters in low‐carbon steels, the predicted habit planes are near {5 5 7}γ. The examples of Fe–0.252C and Fe–0.6C are analyzed in detail along with the resulting orientation relationships which are consistently close to the Kurdjumov–Sachs model. Furthermore, a MATLAB app `Lath Martensite' is provided which allows the application of this model to any other material undergoing an f.c.c. to b.c.c. transformation.

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Section: Introductionmentioning

confidence: 83%

A parameter-free double-shear theory for lath martensite

Koumatos

Muehlemann

2019

Acta Cryst Sect A

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“…The generalizations of the Hadamard jump conditions considered in [4] (see also [23]) are also insufficiently general and tractable. As well as for polycrystals, such generalized jump conditions are potentially relevant for the analysis of nonclassical austenite-martensite interfaces as proposed in [24,25], which have been observed in CuAlNi [26,27], ultra-low hysteresis alloys [28], and which have been suggested to be involved in steel [29].…”

Section: Bicrystals With Two Martensitic Energy Wellsmentioning

confidence: 99%

Geometry of polycrystals and microstructure

Ball

Carstensen

2015

MATEC Web of Conferences

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Abstract. We investigate the geometry of polycrystals, showing that for polycrystals formed of convex grains the interior grains are polyhedral, while for polycrystals with general grain geometry the set of triple points is small. Then we investigate possible martensitic morphologies resulting from intergrain contact. For cubic-totetragonal transformations we show that homogeneous zero-energy microstructures matching a pure dilatation on a grain boundary necessarily involve more than four deformation gradients. We discuss the relevance of this result for observations of microstructures involving second and third-order laminates in various materials. Finally we consider the more specialized situation of bicrystals formed from materials having two martensitic energy wells (such as for orthorhombic to monoclinic transformations), but without any restrictions on the possible microstructure, showing how a generalization of the Hadamard jump condition can be applied at the intergrain boundary to show that a pure phase in either grain is impossible at minimum energy.

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“…Section 3.2) and generally lay the groundwork for mathematical theories of steels based on energy minimisation (see e.g. [Bha03,KM15]). 4.…”

Section: Introductionmentioning

confidence: 99%

A theoretical investigation of orientation relationships and transformation strains in steels

Koumatos

Muehlemann

2017

Acta Crystallogr A Found Adv

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The identification of orientation relationships (ORs) plays a crucial role in the understanding of solid phase transformations. In steels, the most common models of ORs are the ones by Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS). The defining feature of these and other OR models is the matching of directions and planes in the parent face-centred cubic γ phase to ones in the product body-centred cubic/tetragonal α/α' phase. In this article a novel method that identifies transformation strains with ORs is introduced and used to develop a new strain-based approach to phase-transformation models in steels. Using this approach, it is shown that the transformation strains that leave a close-packed plane in the γ phase and a close-packed direction within that plane unrotated are precisely those giving rise to the NW and KS ORs when a cubic product phase is considered. Further, it is outlined how, by choosing different pairs of unrotated planes and directions, other common ORs such as the ones by Pitsch and Greninger-Troiano can be derived. One of the advantages of our approach is that it leads to a natural generalization of the NW, KS and other ORs for different ratios of tetragonality r of the product body-centred tetragonal α' phase. These generalized ORs predict a sharpening of the transformation textures with increasing tetragonality and are thus in qualitative agreement with experiments on steels with varying alloy concentration.

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The morphology of lath martensite: a new perspective

Cited by 5 publications

References 18 publications

A parameter-free double-shear theory for lath martensite

A parameter-free double-shear theory for lath martensite

Geometry of polycrystals and microstructure

A theoretical investigation of orientation relationships and transformation strains in steels

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