Mechanisms for deformation induced hexagonal close-packed structure to face-centered cubic structure transformation in zirconium

Zhao, Henglv; Hu, Xinyi; Song, Min; Ni, Song

doi:10.1016/j.scriptamat.2017.01.034

Cited by 78 publications

(25 citation statements)

References 14 publications

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“…Despite the fact that for the last 60 years, nearly all the theoretical models and experimental observations have been interpreted in terms of twinning dislocations or The notion of "twinning dislocations" has been progressively enlarged to displacive phase transformations. For fcc-hcp and hcp-fcc transformations, the classical models imply the coordinate displacement of partial Shockley dislocations, which are supposed to be created by a pole or similar complex mechanism [80][81][82][83]. For fcc-bcc transformations, we have seen in Figure 7 that Olson and Cohen [56,57] used partial dislocations in order to correct the initial hard-sphere Bogers and Burgers model [53].…”

Section: Twinning Dislocations Replaced By Transformation Waves and Dmentioning

confidence: 99%

Shifting the Shear Paradigm in the Crystallographic Models of Displacive Transformations in Metals and Alloys

Cayron

2018

Crystals

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Deformation twinning and martensitic transformations are characterized by the collective displacements of atoms, an orientation relationship, and specific morphologies. The current crystallographic models are based on the 150-year-old concept of shear. Simple shear is a deformation mode at constant volume, relevant for deformation twinning. For martensitic transformations, a generalized version called invariant plane strain is used; it is associated with one or two simple shears in the phenomenological theory of martensitic crystallography. As simple shears would involve unrealistic stresses, dislocation/disconnection-mediated versions of the usual models have been developed over the last decades. However, a fundamental question remains unsolved: how do the atoms move? The aim of this paper is to return to a crystallographic approach introduced a few years ago; the approach is based on a hard-sphere assumption and linear algebra. The atomic trajectories, lattice distortion, and shuffling (if required) are expressed as analytical functions of a unique angular parameter; the habit planes are calculated with the simple "untilted plane" criterion; non-Schmid behaviors associated with some twinning modes are also predicted. Examples of steel and magnesium alloys are taken from recent publications. The possibilities offered in mechanics and thermodynamics are briefly discussed.

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Section: Twinning Dislocations Replaced By Transformation Waves and Dmentioning

confidence: 99%

Shifting the Shear Paradigm in the Crystallographic Models of Displacive Transformations in Metals and Alloys

Cayron

2018

Crystals

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“…Interestingly, this γ → ε transformation mechanism does not necessarily explain the occurrence of γ nanolaminates inside the HCP ε blocks after deformation. This may rather be due to a reverse transformation (ε → γ) inside the HCP ε block. In order to discuss this hypothesis, three factors, viz., the stacking fault energy, local temperature, and local stress−strain fields, have to be considered.…”

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confidence: 99%

“…Theoretically, a reverse transformation from the HCP ε to the FCC γ can be achieved through the motion of Shockley partials on every second {0001} basal plane with Burgers vectors

\frac{a}{3}

1 \bar{1} 00

> . They have three equivalent glide directions, which can generate stacking faults (i.e., nanoscale FCC structure) in the HCP matrix with negligible volume expansion . Upon strain loading, the sliding of Shockley partials in the HCP ε block of the dual‐phase HEA is achieved by two possible ways ( Figure ).…”

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confidence: 99%

Bidirectional Transformation Enables Hierarchical Nanolaminate Dual‐Phase High‐Entropy Alloys

et al. 2018

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conventional nanostructures, for instance with grain sizes below a critical value of ≈50 nm, can experience softening due to grain boundary sliding. [11,12] Over the past years, a novel approach to microstructure design, known as hierarchical laminate structure, has shown to greatly improve strength and ductility of conventional materials simultaneously, such as Ti alloys and steels, through massive microstructure refinement. [13][14][15][16] Typically, such materials with hierarchical laminate structures consist of a parent phase serving as soft matrix to improve ductility and a hard product phase impeding dislocation motion to strengthen the microstructure. Unfortunately, such heterogeneous materials with high local mechanical disparity among their constituting phases are often prone to internal damage initiation, thus limiting ductility to 3.8-15% for Ti alloys, [13,14] 20-33% for medium Mn steels, [17] and 23-33% for stainless steels. [16] Therefore, the mechanical properties of such hierarchical laminate materials need to be further improved to minimize the probability of internal damage and failure. Also, creating laminate structures in bulk materials often requires imposing complex processing methods, e.g., accumulative roll bonding. [18] Interestingly, a recently developed dual-phase high-entropy alloy (HEA) also exhibits a simultaneous increase of strength and ductility after grain refinement [19][20][21][22][23] as highlighted in Figure 1. The excellent strength-ductility combination of the novel dual-phase HEA has been reported to be related to the transformationinduced plasticity (TRIP) effect, i.e., the displacive phase transformation from the face-centered cubic (FCC γ) matrix into the hexagonal close-packed (HCP ε) phase upon deformation. [19,22] Depending on the magnitude of the stacking fault energy, different compositional variants of recently developed HEAs have shown deformation modes with planar dislocation slip, [24,25] twinning induced plasticity (TWIP), [26] or TRIP effect. [22] Here, we observe another state which is thermodynamically characterized by a similar stability of two co-existing phases (FCC γ and HCP ε). This means that the stacking fault energy of the FCC matrix must assume a near-zero yet positive value so that forward (γ → ε) and backward (ε → γ) transformations can be both triggered in the same material and loading state.We studied the deformation mechanisms in the dual-phase HEA (Fe 50 Mn 30 Co 10 Cr 10 , at%) in more detail via transmission electron microscopy (TEM) analysis and found that this novel TRIP-assisted HEA gradually develops a hierarchical Microstructural length-scale refinement is among the most efficient approaches to strengthen metallic materials. Conventional methods for refining microstructures generally involve grain size reduction via heavy cold working, compromising the material's ductility. Here, a fundamentally new approach that allows load-driven formation and permanent refinement of a hierarchical nanolaminate structure in a novel high-entropy allo...

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“…The orientation relation of FCC-Ti and HCP-Ti are 〈 0001〉 HCP || 〈 001〉 FCC and {1010} HCP || {110} FCC . Both two distinctive orientation relations between HCP phase and FCC phase were observed simultaneously in cold-rolled pure Zr 25 .…”

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confidence: 83%

Deformation Behavior of Pure Titanium With a Rare HCP/FCC Boundary: An Atomistic Study

et al. 2020

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The compressive and tensile behaviors in a Ti nanopillar with a biphasic hexagonal close-packed (HCP) /face-centered cubic (FCC) phase boundary are theoretically researched using classic molecular dynamic simulation. The results indicate that the HCP/FCC interface and free surface of the nanopillar are the sources of dislocation nucleation. The plastic deformation is mainly concentrated in the metastable FCC phase of the biphasic nanopillar. Under compressive loading, a reverse phase transformation of FCC to the HCP phase is induced by the dislocation glide of multiple Shockley partial dislocations 1 6 <121> under compressive loading. However, for tensile loading a large number of Lomer-Cottrell sessile dislocations and stacking fault nets are formed when the partial dislocations react, which leads to an increase in stress. The formation mechanism of a Lomer-Cottrell sessile dislocation is also studied in detail. Shockley partial dislocations are the dominant mode of plastic deformation behaviors in the metastable FCC phase of the biphasic nanopillar.

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Mechanisms for deformation induced hexagonal close-packed structure to face-centered cubic structure transformation in zirconium

Cited by 78 publications

References 14 publications

Shifting the Shear Paradigm in the Crystallographic Models of Displacive Transformations in Metals and Alloys

Shifting the Shear Paradigm in the Crystallographic Models of Displacive Transformations in Metals and Alloys

Bidirectional Transformation Enables Hierarchical Nanolaminate Dual‐Phase High‐Entropy Alloys

Deformation Behavior of Pure Titanium With a Rare HCP/FCC Boundary: An Atomistic Study

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