The mechanism of bcc α′ nucleation in single hcp ε laths in the fcc γ → hcp ε → bcc α′ martensitic phase transformation

Yang, Xinwei; Sun, Sheng; Zhang, Tong‐Yi

doi:10.1016/j.actamat.2015.05.034

Cited by 123 publications

(31 citation statements)

References 39 publications

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“…The HAADF‐STEM image in Figure d shows that even at the intersection of the ε laminate variants no body‐centered cubic (BCC) martensitic phase is formed. This observation confirms that HCP ε is the only product phase of the transformation from the FCC γ blocks, and other martensite variants, e.g., BCC α′ observed in metastable steels, do not exist in the current dual‐phase HEA.…”

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confidence: 76%

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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confidence: 76%

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

et al. 2018

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“…10(d) /2 101 on (¯) 111 planes, respectively, as shown in Fig. 10(e), which causes the geometrical misorientation (Yang et al, 2014(Yang et al, , 2015. The discovered stress-dependent creep mechanisms are also shown by the MD snapshots in Fig.…”

Section: Hrtem and MD Simulation Evidences On The Creep Mechanismsmentioning

confidence: 72%

Time, stress, and temperature-dependent deformation in nanostructured copper: Stress relaxation tests and simulations

Yang

Wang

et al. 2016

Acta Materialia

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a b s t r a c tIn the present work, we performed experiments, atomistic simulations, and high-resolution electron microscopy (HREM) to study the creep behaviors of the nanotwinned (nt) and nanograined (ng) copper at temperatures of 22°C (RT), 40°C, 50°C, 60°C, and 70°C. The experimental data at various temperatures and different sustained stress levels provide sufficient information, which allows one to extract the deformation parameters reliably. The determined activation parameters and microscopic observations indicate transition of creep mechanisms with variation in stress level in the nt-Cu, i.e., from the Coble creep to the twin boundary (TB) migration and eventually to the perfect dislocation nucleation and activities. The experimental and simulation results imply that nanotwinning could be an effective approach to enhance the creep resistance of twin-free ng-Cu. The experimental creep results further verify the newly developed formula (Yang et al., 2016) that describes the time-, stress-, and temperature-dependent plastic deformation in polycrystalline copper.

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“…The so-called plastic strain-induced transformation takes place. The basic mechanism of nucleation is shear in the intersecting planes of close packing [ 6 , 7 ]. The displacements necessary for the transformation of the fcc structure into bcc are parts of the twinning shear of austenite T : T /3 and 3 T /8, respectively.…”

Section: Introductionmentioning

confidence: 99%

Phase Transformation in 316L Austenitic Steel Induced by Fracture at Cryogenic Temperatures: Experiment and Modelling

et al. 2020

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Investigations by electron backscatter diffraction (EBSD) and X-ray diffraction with the use of synchrotron radiation, as well as parallel extended finite element (XFEM) simulations, reveal the evolution of the 316L stainless steel microstructure in the vicinity of a macro-crack developing at the temperature of liquid helium (4.2 K). The fracture propagation induces a dynamic, highly localized phase transformation of face-centred cubic austenite into α’ martensite with a body-centred cubic structure. Synchrotron studies show that the texture of the primary phase controls the transition process. The austenite grains, tending to the stable Brass orientation, generate three mechanisms of the phase transformation. EBSD studies reveal that the secondary phase particles match the ordered austenitic matrix. Hence, interphase boundaries with the Pitsch disorientation are most often formed and α’ martensite undergoes intensive twinning. The XFEM simulations, based on the experimentally determined kinetics of the phase transformation and on the relevant constitutive relationships, reveal that the macro-crack propagates mainly in the martensitic phase. Synchrotron and EBSD studies confirm the almost 100% content of the secondary phase at the fracture surface. Moreover, they indicate that the boundaries formed then are largely random. As a result, the primary beneficial role of martensite as reinforcing particles is eliminated.

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The mechanism of bcc α′ nucleation in single hcp ε laths in the fcc γ → hcp ε → bcc α′ martensitic phase transformation

Cited by 123 publications

References 39 publications

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

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

Time, stress, and temperature-dependent deformation in nanostructured copper: Stress relaxation tests and simulations

Phase Transformation in 316L Austenitic Steel Induced by Fracture at Cryogenic Temperatures: Experiment and Modelling

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