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3 pages, 157 KiB

Open AccessEditorial

The Behaviours of Alloys under Thermo-Mechanical Treatment

by Maria Cecilia Poletti

Metals 2021, 11(5), 677; https://doi.org/10.3390/met11050677 - 21 Apr 2021

Viewed by 1084

Abstract

The forging of metals is among the oldest working techniques—about 6000 years old [...] Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

Research

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13 pages, 2214 KiB

Open AccessArticle

Integrated Physical-Constitutive Computational Framework for Plastic Deformation Modeling

by Bernhard Viernstein and Ernst Kozeschnik

Metals 2020, 10(7), 869; https://doi.org/10.3390/met10070869 - 30 Jun 2020

Cited by 4 | Viewed by 2152

Abstract

An integrated framework for deformation modeling has been developed, which combines a physical state parameter-based formulation for microstructure evolution during plastic deformation processes with constitutive creep models of polycrystalline materials. The implementations of power law, Coble, Nabarro–Herring and Harper–Dorn creep and grain boundary [...] Read more.

An integrated framework for deformation modeling has been developed, which combines a physical state parameter-based formulation for microstructure evolution during plastic deformation processes with constitutive creep models of polycrystalline materials. The implementations of power law, Coble, Nabarro–Herring and Harper–Dorn creep and grain boundary sliding are described and their contributions to the entire stress response at a virtual applied strain rate are discussed. The present framework simultaneously allows calculating the plastic deformation under prescribed strain rate or constant stress, as well as stress relaxation after preceding stress or strain loading. The framework is successfully applied for the construction of deformation mechanism maps. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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18 pages, 23842 KiB

Open AccessArticle

The Deformation Behavior, Microstructural Mechanism, and Process Optimization of PM/Wrought Dual Superalloys for Manufacturing the Dual-Property Turbine Disc

by Baoyun Zhang, Xiaoming Liu, Hao Yang and Yongquan Ning

Metals 2019, 9(10), 1127; https://doi.org/10.3390/met9101127 - 21 Oct 2019

Cited by 7 | Viewed by 2864

Abstract

With the rapid development of modern aviation industry, dual-property turbine disc with fine comprehensive performance plays an important role in raising the thrust-to-weight ratio of the aero-engine. For manufacturing dual-property turbine disc, the powder metallurgy superalloy (PM) with excellent creep resistance was chosen [...] Read more.

With the rapid development of modern aviation industry, dual-property turbine disc with fine comprehensive performance plays an important role in raising the thrust-to-weight ratio of the aero-engine. For manufacturing dual-property turbine disc, the powder metallurgy superalloy (PM) with excellent creep resistance was chosen as rim material, and the wrought superalloy with fine equiaxed grains was chosen as bore material. Electron beam welding was carried out on the PM/wrought dual superalloys. Hot compression tests were conducted on the PM/Wrought dual superalloys at temperatures of 1020–1140 °C and strain rates of 0.001–1.0 s⁻¹. Deformation behavior and microstructure evolution have been investigated to study the deformation and recrystallization mechanism during hot deformation process. The results showed that PM/Wrought dual superalloy presents the similar flow behavior to single alloys and flow stress decreases significantly with the increase of deformation temperature or the decrease of strain rate. The apparent activation energy of deformation at the strain of 0.2 was determined as being 780.07 kJ·mol⁻¹. The constitutive equation was constructed for modeling the hot deformation of PM/Wrought dual superalloy. Meanwhile, the processing map approach was further adopted to optimize the manufacturing process for the dual-property turbine disc. Additionally, a new instability criterion was proposed: the “cliff” and “valley” in the power dissipation map are determined as sufficient conditions for flow instability. The optimum processing parameter for manufacturing the PM/Wrought dual-property turbine disc can be obtained to enhance the mechanical properties, based on the analysis of processing map technology and microstructural mechanism. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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14 pages, 6503 KiB

Open AccessArticle

In-Situ Synchrotron X-Ray Diffraction of Ti-6Al-4V During Thermomechanical Treatment in the Beta Field

by Fernando Warchomicka, David Canelo-Yubero, Egon Zehetner, Guillermo Requena, Andreas Stark and Cecilia Poletti

Metals 2019, 9(8), 862; https://doi.org/10.3390/met9080862 - 07 Aug 2019

Cited by 14 | Viewed by 3820

Abstract

This work aims to identify the mechanisms of restoration occurring in Ti-6Al-4V during hot plastic deformation and subsequent heat treatment. The allotropic phase transformation that occurs during cooling distorts the interpretation of the restoration mechanisms taking place at high temperatures. Therefore, analysis of [...] Read more.

This work aims to identify the mechanisms of restoration occurring in Ti-6Al-4V during hot plastic deformation and subsequent heat treatment. The allotropic phase transformation that occurs during cooling distorts the interpretation of the restoration mechanisms taking place at high temperatures. Therefore, analysis of deformed samples by conventional microscopy have led to controversies in the interpretation of the main dynamic restoration mechanism. Additionally, static restoration of the microstructure can occur during slow cooling, modifying the microstructure. These facts were mainly the reasons why discontinuous dynamic recrystallization and/or dynamic recovery has been reported as the main dynamic restoration mechanism for Ti-6Al-4V. In this work, we use in-situ synchrotron X-ray diffraction combined with conventional microscopy to determine the dynamic and static mechanisms of restoration during and after deformation at different strain rates. The results show dynamic recovery as main mechanism of restoration during deformation in the β field, denoted by sub-grain formation and a misorientation dependency of the strain rate. After deformation, static recrystallization, grain growth, and coarsening of the β grains can be observed, especially at strain rates higher than 0.1 s⁻¹. It is also demonstrated that the nucleation of new grains can occur within the very first seconds of the isothermal heat treatment. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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15 pages, 10011 KiB

Open AccessArticle

Dislocation Density-Based Modeling of Dynamic Recrystallized Microstructure and Process in Friction Stir Spot Welding of AA6082

by Zeng Gao, Jianguang Feng, Zhenjiang Wang, Jitai Niu and Christof Sommitsch

Metals 2019, 9(6), 672; https://doi.org/10.3390/met9060672 - 10 Jun 2019

Cited by 11 | Viewed by 3520

Abstract

This work mainly focuses on a series of microstructural analysis and predictions regarding dynamic recrystallization behavior, change in grain size, and dislocation density. Additionally, this study includes the shape prediction of the stir zone formed during friction stir spot welding. Microstructure analysis of [...] Read more.

This work mainly focuses on a series of microstructural analysis and predictions regarding dynamic recrystallization behavior, change in grain size, and dislocation density. Additionally, this study includes the shape prediction of the stir zone formed during friction stir spot welding. Microstructure analysis of the joint reveals that the mechanism of dynamic recrystallization in the stir zone is geometric dynamic recrystallization. A set of constitutive equations based on dislocation density is established and implemented in DEFORM-3D software to predict dynamic recrystallization during friction stir spot welding of AA6082. From the experimental and model predictions, it is observed that the original microstructure in the stir zone is completely replaced by a recrystallized fine grained microstructure. There is satisfactory agreement between the experimental grain size and the simulated results. In addition, the predicted shape of the stir zone fits quite well with the experimental shape as well. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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17 pages, 6525 KiB

Open AccessArticle

Increase in the Mechanical Strength of Mg-8Gd-3Y-1Zn Alloy Containing Long-Period Stacking Ordered Phases Using Equal Channel Angular Pressing Processing

by Gerardo Garces, Pablo Pérez, Rafael Barea, Judit Medina, Andreas Stark, Norbert Schell and Paloma Adeva

Metals 2019, 9(2), 221; https://doi.org/10.3390/met9020221 - 13 Feb 2019

Cited by 16 | Viewed by 2683

Abstract

The evolution of the microstructure and mechanical properties during equal channel angular pressing processing has been studied in an extruded Mg-Gd-Y-Zn alloy containing long-period stacking ordered phases. After extrusion, the microstructure is characterized by the presence of long-period stacking ordered fibers elongated along [...] Read more.

The evolution of the microstructure and mechanical properties during equal channel angular pressing processing has been studied in an extruded Mg-Gd-Y-Zn alloy containing long-period stacking ordered phases. After extrusion, the microstructure is characterized by the presence of long-period stacking ordered fibers elongated along the extrusion direction within the magnesium matrix. The grain structure is a mixture of randomly oriented dynamic recrystallized and coarse highly oriented non-dynamic recrystallized grains. Rare-earth atoms are in solid solution after extrusion at 400 °C and precipitation takes place during the thermal treatment at 200 °C. Precipitation of β’ prismatic plates and lamellar γ’ in the basal plane increases the tensile yield stress from 325 to 409 MPa. During equal channel angular pressing processing at 300 °C, the volume fraction of dynamic recrystallized grains continuously increases with the strain introduced during the equal channel angular pressing process. Precipitation of β phase is equally observed at grain boundaries of the ECAPed alloy. Dynamic recrystallized grain size decreases from 1.8 µm in the extruded material to 0.5 µm in the ECAPed alloy. Thermal treatment at 200 °C of ECAPed materials results in an increase of the yield stress up to 456 MPa, which is maintained up to 200 °C. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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8 pages, 3921 KiB

Open AccessArticle

Effect of Preheating Temperature on the Microstructure and Tensile Properties of 6061 Aluminum Alloy Processed by Hot Rolling-Quenching

by Qing-Long Zhao, Tong-Tong Shan, Run Geng, Yang-Yang Zhang, Hong-Yun He, Feng Qiu and Qi-Chuan Jiang

Metals 2019, 9(2), 182; https://doi.org/10.3390/met9020182 - 03 Feb 2019

Cited by 9 | Viewed by 4022

Abstract

The present work investigates the microstructure and tensile properties of a hot rolled 6061 alloy quenched by cold rolls (RQ) at different preheating temperatures. The preheating temperature strongly affects microstructure evolution and mechanical properties. Low preheating temperature (490 °C) resulted in both low [...] Read more.

The present work investigates the microstructure and tensile properties of a hot rolled 6061 alloy quenched by cold rolls (RQ) at different preheating temperatures. The preheating temperature strongly affects microstructure evolution and mechanical properties. Low preheating temperature (490 °C) resulted in both low strength and low elongation. The RQ alloy preheated at 540 °C exhibited improved ductility compared to those subjected to T6 and T8 temper, and comparable strength to that after T8 temper. The dynamic recovery during hot rolling contributed to the improved tensile elongation and retained work hardening. High preheating temperature also led to pronounced ageing hardening during short-term ageing. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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9 pages, 4040 KiB

Open AccessArticle

Strengthening Al-Zn-Mg Alloys via Ultra-Fine Lamella Structures Containing a High Density of Dislocations and Clusters

by Yonggui Qin, Sicong Lin, Shenbao Jin and Jizi Liu

Metals 2019, 9(2), 140; https://doi.org/10.3390/met9020140 - 28 Jan 2019

Cited by 4 | Viewed by 2577

Abstract

A new method of thermo-mechanical processing has been designed by introducing pre-aging before general cold rolling for an Al-Zn-Mg alloy. This process results in an increase of 200 MPa in yield strength compared to that of the peak-aged samples. The microstructures were examined [...] Read more.

A new method of thermo-mechanical processing has been designed by introducing pre-aging before general cold rolling for an Al-Zn-Mg alloy. This process results in an increase of 200 MPa in yield strength compared to that of the peak-aged samples. The microstructures were examined by transmission electron microscope and X-ray diffraction. It has been found that the enhanced strength is mainly contributed to by ultra-fine lamella structures containing a high density of dislocations pinned by nanoprecipitates. Extra strength is provided by the “interlocking” of precipitates and dislocations. Fractographic features analysis shows that crack propagation along the interface of the lamella structures is the direct reason for resulting in fracture, due to intra-granular strength exceeding grain boundary cohesion. Full article

(This article belongs to the Special Issue The Behaviours of Alloys under Thermo-Mechanical Treatment)

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