A theoretical investigation of orientation relationships and transformation strains in steels

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 tetragonalityrof 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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Quantitative Analysis of Variant Selection and Orientation Relationships during the γ-to-α Phase Transformation in Hot-Rolled TRIP Steels

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.89-91.359 ◽

2010 ◽

Vol 89-91 ◽

pp. 359-364 ◽

Cited By ~ 1

Author(s):

Loïc Malet ◽

Pascal J. Jacques ◽

Stéphane Godet

Keyword(s):

Phase Transformation ◽

Orientation Relationship ◽

Hot Deformation ◽

High Performance ◽

Statistical Treatment ◽

Phenomenological Theory ◽

Variant Selection ◽

Orientation Relationships ◽

Α Phase ◽

Hot Rolled

The orientation relationships that apply to the fcc (γ) – bcc (α) phase transformation in high-performance hot-rolled TRIP-aided steels were characterised by EBSD techniques. A statistical treatment of the experimental data allows the mean orientation relationship to be determined. This mean orientation relationship was compared to the models commonly proposed in the literature and confronted qualitatively to the predictions of the phenomenological theory of martensite crystallography (PTMC). The variant selection phenomenon was also characterized quantitatively at the level of individual austenite grains. The reconstruction of the EBSD maps evidences that bainite grows by packets in which the bainite laths share a common {111}γ plane in the austenite. This growth mechanism is not influenced by the prior hot deformation of the austenite. The hot deformation has a critical influence on the number of packets that forms. The analysis of the crystallographic features of the bainite packets reveals that all possible variants are formed in a packet, though in different proportions.

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Evolution of Crystallographic Texture in Pure Iron and Commercial Steels by γ to α Transformation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.2657 ◽

2012 ◽

Vol 706-709 ◽

pp. 2657-2662 ◽

Cited By ~ 2

Author(s):

Jin Kyung Sung ◽

Dong Nyung Lee

Keyword(s):

Grain Size ◽

Phase Transformation ◽

Pure Iron ◽

Strain Energy ◽

Elastic Anisotropy ◽

Sheet Thickness ◽

Surface Oxidation ◽

Α Phase ◽

Novel Method ◽

Clean Metal

A novel method has been discovered for controlling the crystallographic orientation of pure iron using the γ to α phase transformation. When pure iron with clean metal surfaces undergoes the γ to α phase transformation, it develops a strong cube-on-face texture ({100}<0vw>) with the grain size being larger than the sheet thickness. The mechanism controlling the <100> orientation obtained is associated with the fact that the {100} faces are elastically compliant so that the <100> texture can develop in a manner consistent with minimization of strain energy. However, in commercial steels, although so many texture analyses have been conducted, the cube-on-face texture has been rarely observed. According to thermodynamic analysis, surface oxidation in commercial steels appears to be responsible for the deterioration of the <100> texture. This phenomenon can be explained in terms of the modification of the inherent elastic anisotropy of metal surface by the surface oxidation.

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Direct imaging of order-disorder and antiphase domain structures in Ti3Al intermetallic compound

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100175533 ◽

1990 ◽

Vol 48 (4) ◽

pp. 480-481

Author(s):

H. Q. Ye ◽

T.S. Xie ◽

D. Li

Keyword(s):

Intermetallic Compound ◽

Volume Fraction ◽

Fundamental Problem ◽

Antiphase Domain ◽

Atomic Scale ◽

Orientation Relationships ◽

Domain Structures ◽

Α Phase ◽

Diffraction Patterns ◽

Two Phases

The Ti3Al intermetallic compound has long been recognized as potentially useful structural materials. It offers attractive strength to weight and elastic modulus to weight ratios. Recent work has established that the addition of Nb to Ti3Al ductilized this compound. In this work the fundamental problem of this alloy, i.e. order-disorder and antiphase domain structures was investigated at the atomic scale.The Ti3Al+10at%Nb alloys used in this study were treated at 1060°C and then aged at 700°C for 2 hours. The specimens suitable for TEM were prepared by standard jet electrolytic-polishing technique. A JEM-200CX electron microscope with an interpretable resolution of about 0.25 nm was used for HREM.The [100] and [001] projections of the α2 phase were shown in Fig.l.The alloy obtained consist of at least two phases-α2(Ti3Al) and β0 structures. Moreover, a disorder α phase with small volume fraction was also observed. Fig.2 gives [100] and [001] diffraction patterns of the α2 phase. Since lattice parameters of the ordered α2 (a=0.579, c=0.466 nm) and disorder α phase (a0=0.294≈a/2, c0=0.468 nm) are almost the same, their diffraction patterns are difficult to be distinguished when they are overlapped with epitaxial orientation relationships.

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Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19883072 ◽

1988 ◽

Vol 53 (12) ◽

pp. 3072-3079

Author(s):

Mojmír Skokánek ◽

Ivo Sláma

Keyword(s):

Heat Capacity ◽

Phase Transformation ◽

Phase Transformations ◽

Dimethyl Sulfoxide ◽

Liquidus Temperature ◽

Molar Heat Capacity ◽

Solid Phase ◽

Zinc Nitrate ◽

Heat Capacities ◽

Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

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Effects of α–γ–α Phase Transformation on the ∑3 Boundaries in High-Purity Iron

Journal of Materials Engineering and Performance ◽

10.1007/s11665-021-05866-2 ◽

2021 ◽

Author(s):

Syed Ejaz Hussain ◽

Weiguo Wang ◽

Xinfu Gu ◽

Yunkai Cui ◽

Ahua Du ◽

...

Keyword(s):

Phase Transformation ◽

High Purity ◽

Α Phase ◽

Purity Iron ◽

High Purity Iron

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Oxygen Induced Phase Transformation in TC21 Alloy with a Lamellar Microstructure

Metals ◽

10.3390/met11010163 ◽

2021 ◽

Vol 11 (1) ◽

pp. 163

Author(s):

Shu Wang ◽

Yilong Liang ◽

Hao Sun ◽

Xin Feng ◽

Chaowen Huang

Keyword(s):

Electron Microscopy ◽

Phase Transformation ◽

Oxygen Uptake ◽

Titanium Alloys ◽

Electron Backscatter Diffraction ◽

Lamellar Microstructure ◽

Α Phase ◽

Transmission Electron ◽

The Matrix ◽

Oxygen Ingress

The main objective of the present study was to understand the oxygen ingress in titanium alloys at high temperatures. Investigations reveal that the oxygen diffusion layer (ODL) caused by oxygen ingress significantly affects the mechanical properties of titanium alloys. In the present study, the high-temperature oxygen ingress behavior of TC21 alloy with a lamellar microstructure was investigated. Microstructural characterizations were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Obtained results demonstrate that oxygen-induced phase transformation not only enhances the precipitation of secondary α-phase (αs) and forms more primary α phase (αp), but also promotes the recrystallization of the ODL. It was found that as the temperature of oxygen uptake increases, the thickness of the ODL initially increases and then decreases. The maximum depth of the ODL was obtained for the oxygen uptake temperature of 960 °C. In addition, a gradient microstructure (αp + β + βtrans)/(αp + βtrans)/(αp + β) was observed in the experiment. Meanwhile, it was also found that the hardness and dislocation density in the ODL is higher than that that of the matrix.

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