scholarly journals Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2496 ◽  
Author(s):  
Kai Zhu ◽  
Shoujiang Qu ◽  
Aihan Feng ◽  
Jingli Sun ◽  
Jun Shen
Keyword(s):  
Dynamic Recrystallization ◽  
Microstructural Evolution ◽  
Lamellar Microstructure ◽  
Phase Region ◽  
Second Step ◽  
Electron Backscattered Diffraction ◽  
Isothermal Forging ◽  
Continuous Dynamic Recrystallization ◽  
Mixture Phase ◽  
Refinement Mechanism

Multidirectional isothermal forging (MDIF) was used on a Ti-44Al-4Nb-1.5Cr-0.5Mo-0.2B (at. %) alloy to obtain a crack-free pancake. The microstructural evolution, such as dynamic recovery and recrystallization behavior, were investigated using electron backscattered diffraction and transmission electron microscopy methods. The MDIF broke down the initial near-lamellar microstructure and produced a refined and homogeneous duplex microstructure. γ grains were effectively refined from 3.6 μm to 1.6 μm after the second step of isothermal forging. The ultimate tensile strength at ambient temperature and the elongation at 800 °C increased significantly after isothermal forging. β/B2→α2 transition occurred during intermediate annealing, and α2 + γ→β/B2 transition occurred during the second step of isothermal forging. The refinement mechanism of the first-step isothermal forging process involved the conversion of the lamellar structure and discontinuous dynamic recrystallization (DDRX) of γ grains in the original mixture-phase region. The lamellar conversion included continuous dynamic recrystallization and DDRX of the γ laths and bugling of the γ phase. DDRX behavior of γ grains dominated the refinement mechanism of the second step of isothermal forging.

Dynamic Recrystallization Mechanisms on Spot Welding of 6008 Aluminium Alloy to Steel by Friction Stir Welding

2007 ◽  
Vol 558-559 ◽  
pp. 477-483 ◽  
Author(s):  
Sandrine Bozzi ◽  
Anne Laure Etter ◽  
Thierry Baudin ◽  
A. Robineau ◽  
Jean Claude Goussain
Keyword(s):  
Friction Stir Welding ◽  
Dynamic Recrystallization ◽  
Aluminium Alloy ◽  
Dwell Time ◽  
Tensile Tests ◽  
Mechanical Tests ◽  
Welding Parameters ◽  
Electron Backscattered Diffraction ◽  
Friction Stir ◽  
Continuous Dynamic Recrystallization

At the prospect of a lightening of the automobile structures, welded spots have been realized on a stacking of two sheets (a 6008 aluminium alloy on steel) by Friction Stir Welding (FSW). Different process parameters have been tested but only the influence of the dwell time will be described in the present paper. The dwell time corresponds to the time during which the probe stays in rotation at its bottom location before extracting. A study of the microstructures and the crystallographic textures associated to mechanical tests (shear and tensile tests) allowed to determine the best set of welding parameters. The recrystallized area around the welding spot has been characterized by Electron BackScattered Diffraction (EBSD). The aim of the present work is to identify the recrystallization mechanisms which occur during welding, and to understand the influence of the dwell time on the recrystallized area. A mechanism of continuous dynamic recrystallization has been identified since misorientation of sub-boundary increases close to the weld and this for all the dwell times tested. Elsewhere, it has been found that the increase of the dwell time induces a larger recrystallized zone.

scholarly journals Characterization of Microstructural Evolution for a Near-α Titanium Alloy with Different Initial Lamellar Microstructures

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1045 ◽  
Author(s):  
Hui Li ◽  
Zhanglong Zhao ◽  
Yongquan Ning ◽  
Hongzhen Guo ◽  
Zekun Yao
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Microstructural Evolution ◽  
Power Dissipation ◽  
Flow Instability ◽  
Lamellar Microstructure ◽  
Rate Sensitivity ◽  
Lamellar Thickness ◽  
Processing Maps ◽  
Deformation Behaviors

The effects of initial lamellar thickness on microstructural evolution and deformation behaviors of a near-α Ti-5.4Al-3.7Sn-3.3Zr-0.5Mo-0.4Si alloy were investigated during isothermal compression in α + β phase field. Special attention was paid to microstructural conversion mechanisms for α lamellae with different initial thicknesses. The deformation behaviors, including flow stress, temperature sensitivity, and strain rate sensitivity, and processing maps and their dependence on initial lamellar thickness were discussed. The detailed microstructural characterizations in different domains of the developed processing maps were analyzed. The results showed that the peak efficiency of power dissipation decreased with increasing initial lamellar thickness. The interaction effects with different extents of globularization, elongating, kinking, and phase transformation of lamellar α accounted for the variation in power dissipation. The flow instability region appeared to expand more widely for thicker initial lamellar microstructures during high strain rate deformation due to flow localization and local lamellae kinking. The electron backscatter diffraction (EBSD) analyses revealed that the collaborative mechanism of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) promoted the rapid globularization behavior for the thinnest acicular initial microstructure, whereas in case of the initial thick lamellar microstructure, CDRX leading to the fragmentation of lamellae was the dominant mechanism throughout the deformation process.

scholarly journals Macro-mesoscale microstructural evolution modeling under hot forging of a Ti-17 alloy with a lamellar (α+β) starting microstructure

2020 ◽  
Vol 321 ◽  
pp. 13005
Author(s):  
Hiroaki Matsumoto ◽  
Kenta Yamanaka ◽  
Akihiko Chiba ◽  
Yoko Yamabe-Mitarai ◽  
Yoshio Itsumi
Keyword(s):  
Dynamic Recrystallization ◽  
Microstructural Evolution ◽  
Hot Forging ◽  
Fem Simulation ◽  
Constitutive Models ◽  
Fem Analysis ◽  
Dominant Mode ◽  
Strain Rates ◽  
Continuous Dynamic Recrystallization ◽  
Β Phase

Microstructural conversion mechanisms under hot forging process (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10–3 s–1 to 1 s–1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure were experimentally identified in this work. After that, constitutive formulae for predicting the microstructural evolution were established followed by calculation using finite-element (FEM) analysis. In the α phase, a lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. On the other hand, continuous dynamic recrystallization is the dominant mode below the transition temperature, Tβ (880~890 °C) in the β phase. And, at conditions of lower strain rates and higher temperatures, dynamic recovery tends to be more active. For microstructural prediction, a set of constitutive equations modeling the microstructural evolution and forging properties are established by optimizing the experimental data followed by implementation in the DEFORM-3D software package. Herein, microstructural evolution on dynamic globularization process, dynamic recrystallization behavior are predicted according to both approaches of physical model and artificial neural network model followed by FEM simulation. In these calculated results, there is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging.

Continuous Dynamic Recrystallization during Warm Deformation of Tempered Lath Martensite in a Medium Carbon Steel

2012 ◽  
Vol 508 ◽  
pp. 124-127 ◽  
Author(s):  
Un Hae Lee ◽  
Naoya Kamikawa ◽  
Goro Miyamoto ◽  
Tadashi Furuhara
Keyword(s):  
Dynamic Recrystallization ◽  
Microstructural Evolution ◽  
Boundary Migration ◽  
Lath Martensite ◽  
Medium Carbon Steel ◽  
Warm Deformation ◽  
Continuous Dynamic Recrystallization ◽  
Dynamic Recrystallization Behavior ◽  
Fine Grained Structure ◽  
Continuous Dynamic

To Understand the Mechanisms of Accelerated Dynamic Recrystallization Behavior during the Warm Deformation of Martensites, the Tempered Lath Martensite of 0.4C Steel (Fe-0.399%C-1.96%Mn in Mass %) Was Deformed at 650 °C in Compression to Different Reductions, and Microstructural Evolution Was Investigated. During the Deformation, an Initial Lath Martensite Structure with a Complicated Morphology Was Gradually Changed into More Equiaxed Structure. After 50% Reduction and above, an Equiaxed, Fine Grained Structure Mainly Surrounded by High-Angle Boundaries Was Uniformly Formed with Dislocation Substructures, where the Dislocation Density in the Grains Is Relatively Low. Since there Was No Significant Boundary Migration during this Process, this Microstructural Evolution Can Be Termed as Continuous Dynamic Recrystallization.

scholarly journals Deformation and Phase Transformation of Disordered α Phase in the (α + γ) Two-Phase Region of a High-Nb TiAl Alloy

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4817
Author(s):  
Haitao Zhou ◽  
Fantao Kong ◽  
Yanbo Wang ◽  
Xiangwu Hou ◽  
Ning Cui ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Dynamic Recrystallization ◽  
Hot Rolling ◽  
Tial Alloy ◽  
Phase Region ◽  
Two Phase ◽  
Continuous Dynamic Recrystallization ◽  
Α Phase ◽  
Continuous Dynamic ◽  
Lower Temperature

In this paper, the deformation and phase transformation of disordered α phase in the (α + γ) two-phase region in as-forged Ti-44Al-8Nb-(W, B, Y) alloy were investigated by hot-compression and hot-packed rolling. The detailed microstructural evolution demonstrated that the deformed microstructure was significantly affected by the deformation conditions, and the microstructure differences were mainly due to the use of a lower temperature and strain rate. Finer α grains were formed by the continuous dynamic recrystallization of α lamellae and α grains distributed around lamellar colonies. Moreover, the grooved γ grains formed by the phase transformation from α lamellae during hot rolling cooperated with and decomposed α lamellae. A microstructure evolution model was built for the TiAl alloy at 1250 °C during hot rolling.

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Microstructural Evolutions of 2N Grade Pure Al and 4N Grade High-Purity Al during Friction Stir Welding

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3606
Author(s):  
Tomoya Nagira ◽  
Xiaochao Liu ◽  
Kohasaku Ushioda ◽  
Hidetoshi Fujii
Keyword(s):  
Friction Stir Welding ◽  
Dynamic Recrystallization ◽  
Grain Refinement ◽  
High Purity ◽  
Cube Texture ◽  
Grain Structure ◽  
Welding Temperature ◽  
Friction Stir ◽  
Continuous Dynamic Recrystallization ◽  
Dislocation Annihilation

The grain refinement mechanisms along the material flow path in pure and high-purity Al were examined, using the marker insert and tool stop action methods, during the rapid cooling friction stir welding using liquid CO2. In pure Al subjected to a low welding temperature of 0.56Tm (Tm: melting point), the resultant microstructure consisted of a mixture of equiaxed and elongated grains, including the subgrains. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and geometric dynamic recrystallization are the potential mechanisms of grain refinement. Increasing the welding temperature and Al purity encouraged dynamic recovery, including dislocation annihilation and rearrangement into subgrains, leading to the acceleration of CDRX and inhibition of DDRX. Both C- and B/-type shear textures were developed in microstructures consisting of equiaxed and elongated grains. In addition, DDRX via high-angle boundary bulging resulted in the development of the 45° rotated cube texture. The B/ shear texture was strengthened for the fine microstructure, where equiaxed recrystallized grains were fully developed through CDRX. In these cases, the texture is closely related to grain structure development.

scholarly journals Effect of Trace Magnesium Additions on the Dynamic Recrystallization in Cast Alloy 825 after One-Hit Hot-Deformation

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 36
Author(s):  
Munir Al-Saadi ◽  
Wangzhong Mu ◽  
Christopher N. Hulme-Smith ◽  
Fredrik Sandberg ◽  
Pär G. Jönsson
Keyword(s):  
Service Life ◽  
Dynamic Recrystallization ◽  
Hot Deformation ◽  
Cast Alloy ◽  
True Strain ◽  
Peak Strain ◽  
Compression Tests ◽  
Electron Backscattered Diffraction ◽  
Hollomon Parameter ◽  
Test Conditions

Alloy 825 is widely used in several industries, but its useful service life is limited by both mechanical properties and corrosion resistance. The current work explores the effect of the addition of magnesium on the recrystallization and mechanical behavior of alloy 825 under hot compression. Compression tests were performed under conditions representative of typical forming processes: temperatures between 1100 and 1250 °C and at strain rates of 0.1–10 s−1 to a true strain of 0.7. Microstructural evolution was characterized by electron backscattered diffraction. Dynamic recrystallization was found to be more prevalent under all test conditions in samples containing magnesium, but not in all cases of conventional alloy 825. The texture direction ⟨101⟩ was the dominant orientation parallel to the longitudinal direction of casting (also the direction in which the samples were compressed) in samples that contained magnesium under all test conditions, but not in any sample that did not contain magnesium. For all deformation conditions, the peak stress was approximately 10% lower in material with the addition of magnesium. Furthermore, the differences in the peak strain between different temperatures are approximately 85% smaller if magnesium is present. The average activation energy for hot deformation was calculated to be 430 kJ mol−1 with the addition of magnesium and 450 kJ mol−1 without magnesium. The average size of dynamically recrystallized grains in both alloys showed a power law relation with the Zener–Hollomon parameter, DD~Z−n, and the exponent of value, n, is found to be 0.12. These results can be used to design optimized compositions and thermomechanical treatments of alloy 825 to maximize the useful service life under current service conditions. No experiments were conducted to investigate the effects of such changes on the service life and such experiments should now be performed.

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