Hot Deformation Characteristics of Metallic Materials

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Metals and Alloys".

Deadline for manuscript submissions: closed (15 September 2023) | Viewed by 6712

Special Issue Editors

Institute of Materials Engineering, University of Kassel, Kassel, Germany
Interests: mechanical properties; additive manufacturing; fatigue and damage; microstructure; titanium alloys; aluminum alloys
Special Issues, Collections and Topics in MDPI journals
Institute of Materials Engineering, University of Kassel, Mönchebergstraße 3, 34125 Kassel, Germany
Interests: abnormal grain growth; cyclic heat treatment; shape memory alloys; phase transformation; functional properties; additive manufacturing; crystal growth

Special Issue Information

Dear Colleagues,

The hot deformation characteristics of metallic materials have attracted noticeable interest due to their potential to provide key insights into the mechanical and microstructural changes during the high-temperature deformation of metals and alloys. Many engineering applications require parts capable of working at high temperatures, and thus the high-temperature characteristics of materials have to be well understood. Besides, the formability of metallic materials is considerably temperature dependent.

Exploring mechanical responses along with microstructural evolution at high temperatures can play a significant role in the adjustment of warm and hot working process parameters, leading to improved workability and formability. Softening mechanisms (i.e., dynamic recovery and recrystallization and subsequent grain growth) are powerful microstructural tools for designing the mechanical properties of metallic materials under high-temperature deformation. Thus, we invite scientists and researchers to contribute to this Special Issue of Crystals entitled “Hot Deformation Characteristics of Metallic Materials”, focusing on the workability, formability, and microstructural evolution of metallic materials at elevated temperatures.

The potential subjects cover, but are not limited to:

  • High-temperature mechanical properties of metals and alloys;
  • Formability and workability of metallic materials at high temperatures;
  • Microstructural evolution during hot deformation;
  • Softening mechanisms (i.e., dynamic recovery and recrystallization);
  • Normal and abnormal grain growth;
  • Mechanical behavior modeling of metallic materials at elevated temperatures.

Dr. Seyedvahid Sajjadifar
Dr. Malte Vollmer
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Hot deformation characteristics
  • Metals and alloys
  • Microstructure
  • Dynamic recovery
  • Dynamic recrystallization
  • Grain growth
  • Mechanical properties

Published Papers (4 papers)

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Research

12 pages, 2867 KiB  
Article
On the Hot Deformation of a Fe-Al-Ta Iron Aluminide Prepared via Laser Powder Bed Fusion
by Aliakbar Emdadi, Sebastian Bolz, Felix Jensch, Michael Tovar and Sabine Weiß
Crystals 2023, 13(4), 627; https://doi.org/10.3390/cryst13040627 - 05 Apr 2023
Cited by 5 | Viewed by 1139
Abstract
In the present work, a combined process of laser powder bed fusion (LPBF) and hot working in terms of microstructure refinement was investigated for Fe-25Al-1.5Ta alloy samples. Uniaxial compression tests were carried out parallel and perpendicular to the building direction (BD) at 1000 [...] Read more.
In the present work, a combined process of laser powder bed fusion (LPBF) and hot working in terms of microstructure refinement was investigated for Fe-25Al-1.5Ta alloy samples. Uniaxial compression tests were carried out parallel and perpendicular to the building direction (BD) at 1000 °C, where BCC A2-phase was stable, at a strain rate of 0.0013 s−1. The true stress–true strain curves indicated a broad flow stress peak followed by a slight decrease, which is typical for dynamic recrystallization (DRX) of conventional BCC metals such as ferritic iron. A negligible dependence in the flow stress behavior on the compression direction was observed. DRX initiated at a stress of 18.7 MPa for the sample compressed parallel to the BD, corresponding to a true strain of 0.011, and at 18.1 MPa for the samples compressed normal to the BD, which corresponded to a true strain of 0.010. The microstructural investigations by electron backscatter diffraction (EBSD) showed that the relatively coarse and elongated grains of the as-LPBF builds were significantly refined after hot working. The microstructure of the compressed samples mainly consisted deformed grains. These were fragmented by sub-grains bounded by low-angle boundaries independent of the compression axis, indicating the occurrence of dynamic recovery (DRV) during hot working. In addition, a few equiaxed, small grains were observed in the pre-existing grain boundaries, which formed due to DRX. Most pores in the as-LPBF builds were closed after hot compression, particularly in the central region of the deformed specimens where the compressive stress state is dominant. In summary, hot compression reveals a practical thermomechanical post-processing treatment for Fe-Al-Ta iron aluminides built by LPBF. The hot working refines the epitaxially elongated microstructure of the as-LPBF builds by DRV/DRX and reduces the porosity. Full article
(This article belongs to the Special Issue Hot Deformation Characteristics of Metallic Materials)
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11 pages, 7231 KiB  
Article
Elevated Temperature Mechanical Characteristics and Fracture Behavior of a Novel Beta Titanium Alloy
by Seyed Vahid Sajadifar, Hans Jürgen Maier, Thomas Niendorf and Guney Guven Yapici
Crystals 2023, 13(2), 269; https://doi.org/10.3390/cryst13020269 - 03 Feb 2023
Cited by 5 | Viewed by 987
Abstract
In the present work, the elevated-temperature deformation characteristics and microstructural evolution of a Ti-5V-5Mo-5Cr-4Al alloy in solution-treatment conditions were studied under a tensile load at temperatures in the range of 25 to 550 °C and strain rates between 0.001 and 0.1 s−1 [...] Read more.
In the present work, the elevated-temperature deformation characteristics and microstructural evolution of a Ti-5V-5Mo-5Cr-4Al alloy in solution-treatment conditions were studied under a tensile load at temperatures in the range of 25 to 550 °C and strain rates between 0.001 and 0.1 s−1. The results obtained indicated that, essentially, dynamic recovery (DRV) was the dominant softening mechanism in the case of the regimes considered. An analysis based on transmission electron microscopy (TEM) and the assessment of the mechanical behavior of the solution-heat-treated Ti-5V-5Mo-5Cr-4Al alloy revealed that dynamic precipitation (DPN) only took place at a strain rate of 0.001 s−1 and at temperatures of 450 °C and 500 °C. Void coalescence occurred upon an increase in the deformation temperature and a decrease in the strain rate due to a higher rate of diffusion and the provision of sufficient time for growth, respectively. The results obtained in the present study pave the way for the robust processing of this novel β titanium alloy. Depending on the deformation parameters, the deformation characteristics can be governed by either DRV (at moderate temperatures) or DPN (at moderate temperatures and at low rates of deformation). Full article
(This article belongs to the Special Issue Hot Deformation Characteristics of Metallic Materials)
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19 pages, 15212 KiB  
Article
Predicting Flow Stress Behavior of an AA7075 Alloy Using Machine Learning Methods
by Jens Decke, Anna Engelhardt, Lukas Rauch, Sebastian Degener, Seyed Vahid Sajadifar, Emad Scharifi, Kurt Steinhoff, Thomas Niendorf and Bernhard Sick
Crystals 2022, 12(9), 1281; https://doi.org/10.3390/cryst12091281 - 09 Sep 2022
Cited by 3 | Viewed by 1759
Abstract
The present work focuses on the prediction of the hot deformation behavior of thermo-mechanically processed precipitation hardenable aluminum alloy AA7075. The data considered focus on a novel hot forming process at different tool temperatures ranging from 24C to 350C [...] Read more.
The present work focuses on the prediction of the hot deformation behavior of thermo-mechanically processed precipitation hardenable aluminum alloy AA7075. The data considered focus on a novel hot forming process at different tool temperatures ranging from 24C to 350C to set different cooling rates after solution heat-treatment. Isothermal uniaxial tensile tests in the temperature range of 200C to 400C and at strain rates ranging from 0.001 s1 to 0.1 s1 were carried out on four different material conditions. The present paper mainly focuses on a comparative study of modeling techniques based on Machine Learning (ML) and the Zerilli–Armstrong model (Z–A) as reference. Related work focuses on predicting single data points of the curves that the model was trained on. Due to the way data were split with respect to training and testing data, it is possible to predict entire stress–strain curves. The model allows to decrease the number of required laboratory experiments, eventually saving costs and time in future experiments. While all investigated ML methods showed a higher performance than the Z–A model, the extreme Gradient Boosting model (XGB) showed superior results, i.e., the highest error reduction of 91% with respect to the Mean Squared Error. Full article
(This article belongs to the Special Issue Hot Deformation Characteristics of Metallic Materials)
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16 pages, 18609 KiB  
Article
Microstructure and Hot Deformation Behaviour of Twin-Roll Cast AZ31 Magnesium Wire
by Falko Arndt, Susanne Berndorf, Marie Moses, Madlen Ullmann and Ulrich Prahl
Crystals 2022, 12(2), 173; https://doi.org/10.3390/cryst12020173 - 25 Jan 2022
Cited by 2 | Viewed by 2000
Abstract
Due to their low density and high specific strength, magnesium alloys offer great potential as a design material for lightweight construction. An economical and energy-efficient method for the production of magnesium wire is the technology of twin-roll casting. In this work, the deformation [...] Read more.
Due to their low density and high specific strength, magnesium alloys offer great potential as a design material for lightweight construction. An economical and energy-efficient method for the production of magnesium wire is the technology of twin-roll casting. In this work, the deformation behaviour of twin-roll cast and heat-treated AZ31 wire pre-profile is investigated for the first time during the compression test at different temperatures (250–400 °C) and forming speeds (0.01–10 s−1). To obtain optimal parameters, a processing map is created, and the microstructural changes during the hot forming processes are determined by accompanying microstructure characterization through an optical microscope and scanning electron microscope. The heat treatment causes a reduction in segregation and a homogeneous microstructure. The average activating energy for plastic deformation of twin-roll cast and heat-treated magnesium alloy AZ31 is 159.008 kJ·mol1. The instability region of the process map starts at a forming temperature of 250 °C and extends into the range of high forming speeds (1–10 s−1). In this area, cracks in the microstructure can be detected during hot forming. At high temperatures (300–350 °C), dynamic recrystallization at the grain boundaries is observed as the main forming mechanism. Based on these results and observations, existing models for describing the hot forming behaviour of magnesium alloys can be extended and validated. Full article
(This article belongs to the Special Issue Hot Deformation Characteristics of Metallic Materials)
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