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High-Temperature Behavior of Metals

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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 32983

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Prof. Dr. Stefano Spigarelli

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Department of Industrial Engineering and Mathematical Sciences, Marche Polytechnic University, Via Brecce Bianche I-60131, Ancona, Italy
Interests: creep; high-temperature deformation and hot working; steels; aluminum alloys; metal matrix composites
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Prof. Dr. Elisabetta Gariboldi

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Department of Mechanical Engineering, Politecnico di Milano, 20133 Milan, Italy
Interests: high temperature mechanical behavior; creep; high temperature microstructural stability; aluminum alloys
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Dear Colleagues,

The design of new alloys or metal-based composites as well as the optimization of processes involving whichever form of high-temperature deformation cannot disregard the characterization and/or modelling of the high-temperature structural response of the material.

If this has been quite extensively investigated (but not always completely understood or described) for conventional hot working processes, there is still a lot to do to accumulate data and models and properly manage innovative deformation processes including more complex time and temperature combinations, where process-related microstructural changes can severely affect the same processability of the material as well as its final properties (structural or functional).

Similar considerations hold in the case of conventional or innovative metallic materials, where ‘high-temperature deformation’ occurs as a consequence of high-temperature service of the structural components. If extensive scientific literature is available for conventional material and for ‘conventional’ service conditions reproduced by the constant load creep test condition, there is still a lot to do in the field of alloy and processing design in view of widening the temperature and loading ranges of existing or innovative materials, including improving the characterization methods and data for material behavior under complex service conditions (i.e., stress relaxation, environmental effects and combination of repeated cycles, presence of flaws) and modelling high-temperature material behavior in all these situations, while considering the need of extended ranges of applicability of these models. The knowledge of the effects on the initial microstructure as well as the microstructural changes taking place during in-service deformation are of course of paramount importance for the optimization of high-temperature structural alloys.

The main focus on the Special Issue ‘High-Temperature Behavior of Metals” is to collect contributions dealing with a wide range of metallic materials and presenting the recent advances in the field of high-temperature structural behavior of metallic materials, which is of interest during both the manufacturing and the service stages of the components’ life and which is intimately linked to microstructural features, their evolution with deformation or exposure time, and thus other material characteristics of potential interest for specific applications.

Prof. Dr. Stefano Spigarelli
Prof. Dr. Elisabetta Gariboldi
Guest Editors

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Keywords

High-temperature structural behavior
Hot working
Creep
Creep-fatigue
Relaxation
High-temperature toughness
Microstructural stability
Deformation-induced microstructural changes
Deformation-induced functional property changes
Modelling
Alloy design

Published Papers (13 papers)

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Editorial

Jump to: Research, Review

5 pages, 199 KiB

Open AccessEditorial

High-Temperature Behavior of Metals

by Elisabetta Gariboldi and Stefano Spigarelli

Metals 2021, 11(7), 1128; https://doi.org/10.3390/met11071128 - 16 Jul 2021

Viewed by 1332

Abstract

The design of new alloys as well as the optimization of processes involving whichever form of high-temperature deformation cannot disregard the characterization and/or modelling of the high-temperature structural response of the material [...] Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

Research

Jump to: Editorial, Review

15 pages, 109052 KiB

Open AccessArticle

Weldability and Damage Evaluations of Fresh-to-Aged Reformer Furnace Tubes

by Chengming Fuyang, Yang Zhou, Bing Shao, Tianyu Zhang, Xiaofeng Guo, Jianming Gong and Xiaowei Wang

Metals 2021, 11(6), 900; https://doi.org/10.3390/met11060900 - 31 May 2021

Cited by 2 | Viewed by 1848

Abstract

The microstructures and tensile properties of fresh and aged reformer furnace tubes and a fresh-to-aged welded joint were investigated to assess the weldability of fresh-to-aged reformer furnace tubes. Damage evaluation of the fresh-to-aged welded joint was also carried out using the modified Kachanov–Rabotnov model. The experimental results showed that M₇C₃ carbide transforms into M₂₃C₆ carbide and secondary carbides precipitate in the matrix after aging treatment. With continuous exposure, the interdendritic precipitates coalesced and coarsened and the number of secondary carbides reduced gradually. Microdefects were absent in the fresh-to-aged welded joint, and the tensile properties of the welded joint were close to the as-cast alloy, which confirms the weldability of fresh-to-aged furnace tubes. According to the results of the simulation, stress redistribution occurred during the creep process and the peak damage of the welded joint was located in the aged tube. The maximum damage of the fresh-to-aged welded joint reached 34.01% at 1.5 × 10⁵ h. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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18 pages, 15893 KiB

Open AccessArticle

High Temperature Behavior of Al-7Si-0.4Mg Alloy with Er and Zr Additions

by Elisabetta Gariboldi, Chiara Confalonieri and Marco Colombo

Metals 2021, 11(6), 879; https://doi.org/10.3390/met11060879 - 28 May 2021

Cited by 2 | Viewed by 2811

Abstract

In recent years, many efforts have been devoted to the development of innovative Al-based casting alloys with improved high temperature strength. Research is often oriented to the investigation of the effects of minor element additions to widely diffused casting alloys. The present study focuses on Al-7Si-0.4Mg (A356) alloy with small additions of Er and Zr. Following previous scientific works on the optimization of heat treatment and on tensile strength, creep tests were carried out at 300 °C under applied stress of 30 MPa, a reference condition for creep characterization of innovative high-temperature Al alloys. The alloys containing both Er and Zr displayed a lower minimum creep strain rate and a longer time to rupture. Fractographic and microstructural analyses on crept and aged specimens were performed to understand the role played by eutectic silicon, by the coarse intermetallics and by α-Al matrix ductility. The creep behavior in tension of the three alloys has been discussed by comparing them to tension and compression creep curves available in the literature for Al-7Si-0.4Mg improved by minor elemental additions. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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14 pages, 7391 KiB

Open AccessArticle

Microstructural Evolution of 9CrMoW Weld Metal in a Multiple-Pass Weld

by Yu-Lun Chuang, Chu-Chun Wang, Tai-Cheng Chen, Ren-Kae Shiue and Leu-Wen Tsay

Metals 2021, 11(6), 847; https://doi.org/10.3390/met11060847 - 21 May 2021

Cited by 1 | Viewed by 1542

Abstract

9CrMoW steel tubes were welded in multiple passes by gas-tungsten arc welding. The reheated microstructures in the Gr. 92 weld metal (WM) of a multiple-pass weld were simulated with an infrared heating system. Simulated specimens after tempering at 760 °C/2 h were subjected to constant load creep tests either at 630 °C/120 MPa or 660 °C/80 MPa. The simulated specimens were designated as the over-tempered (OT, below A_C1, i.e., WT-820T) and partially transformed (PT, below A_C3, i.e., WT-890T) samples. The transmission electron microscope (TEM) micrographs demonstrated that the tempered WM (WT) displayed coarse martensite packets with carbides along the lath and grain boundaries. Cellular subgrains and coarse carbides were observed in the WT-820T sample. A degraded lath morphology and numerous carbides in various dimensions were found in the WT-890T sample. The grain boundary map showed that the WT-820T sample had the same coarse-grained structure as the WT sample, but the WT-890T sample consisted of refined grains. The WT-890T samples with a fine-grained structure were more prone to creep fracture than the WT and WT-820T samples were. Intergranular cracking was more likely to occur at the corners of the crept samples, which suffered from high strain and stress concentration. As compared to the Gr. 91 steel or Gr. 91 WM, the Gr. 92 WM was more stable in maintaining its original microstructures under the same creep condition. Undegraded microstructures of the Gr. 92 WM strained at elevated temperatures were responsible for its higher resistance to creep failure during the practical service. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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27 pages, 15676 KiB

Open AccessArticle

High-Temperature Oxidation Behaviour of AISI H11 Tool Steel

by Tilen Balaško, Maja Vončina, Jaka Burja, Barbara Šetina Batič and Jožef Medved

Metals 2021, 11(5), 758; https://doi.org/10.3390/met11050758 - 04 May 2021

Cited by 7 | Viewed by 3148

Abstract

The high-temperature oxidation of hot-work tool steel AISI H11 was studied. The high-temperature oxidation was investigated in two conditions, the soft annealed condition, and the hardened and tempered condition. First, calculations of the compositions of the oxide layers formed were carried out using the CALPHAD method. The samples were oxidised in a chamber furnace and in a simultaneous thermal analysis instrument, for 100 h in the temperature range between 400 °C and 700 °C. The first samples were used for metallographic (optical microscopy and scanning electron microscopy) and X-ray diffraction analysis of the formed oxide layers, and the second ones for the analysis of the oxidation kinetics by thermogravimetric analysis. Equations describing the high-temperature oxidation kinetics were derived. The kinetics can be described by three mathematical functions, namely: exponential, parabolic, and cubic. However, which function best describes the kinetics depends on the oxidation temperature and the thermal condition of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. The oxide layers consist of three sublayers, the inner one being spinel-like oxide (Fe, Cr)₃O₄, the middle one a mixture of magnetite and hematite and the outer one of hematite. At 700 °C there is also some wüstite in the inner oxide sublayer of the soft annealed sample. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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21 pages, 10056 KiB

Open AccessFeature PaperArticle

Influence of Grain Orientation Distribution on the High Temperature Fatigue Behaviour of Notched Specimen Made of Polycrystalline Nickel-Base Superalloy

by Benedikt Engel, Sebastian Ohneseit, Lucas Mäde and Tilmann Beck

Metals 2021, 11(5), 731; https://doi.org/10.3390/met11050731 - 29 Apr 2021

Cited by 5 | Viewed by 1828

Abstract

Two different material batches made of random and textured orientated polycrystalline nickel-base superalloy René80 were investigated under isothermal low cycle fatigue tests at 850 °C for a notched specimen geometry. In contrast to a smooth specimen geometry, no significant improvement in fatigue behaviour of the notched specimen could be observed for the textured material. Finite element simulations reveal an area along the notch where high stiffness evolves for the textured material, which lead to nearly similar shear stresses in the slip systems compared to a random orientation distribution and therefore to no distinct differences in the lifetime. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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18 pages, 12783 KiB

Open AccessArticle

Hot Deformation Behavior of a Ni-Based Superalloy with Suppressed Precipitation

by Franco Lizzi, Kashyap Pradeep, Aleksandar Stanojevic, Silvana Sommadossi and Maria Cecilia Poletti

Metals 2021, 11(4), 605; https://doi.org/10.3390/met11040605 - 08 Apr 2021

Cited by 10 | Viewed by 2463

Abstract

Inconel^®718 is a well-known nickel-based super-alloy used for high-temperature applications after thermomechanical processes followed by heat treatments. This work describes the evolution of the microstructure and the stresses during hot deformation of a prototype alloy named IN718WP produced by powder metallurgy with similar chemical composition to the matrix of Inconel^®718. Compression tests were performed by the thermomechanical simulator Gleeble^®3800 in a temperature range from 900 to 1025 °C, and strain rates scaled from 0.001 to 10 s⁻¹. Flow curves of IN718WP showed similar features to those of Inconel^®718. The relative stress softening of the IN718WP was comparable to standard alloy Inconel^®718 for the highest strain rates. Large stress softening at low strain rates may be related to two phenomena: the fast recrystallization rate, and the coarsening of micropores driven by diffusion. Dynamic recrystallization grade and grain size were quantified using metallography. The recrystallization grade increased as the strain rate decreased, although showed less dependency on the temperature. Dynamic recrystallization occurred after the formation of deformation bands at strain rates above 0.1 s⁻¹ and after the formation of subgrains when deforming at low strain rates. Recrystallized grains had a large number of sigma 3 boundaries, and their percentage increased with strain rate and temperature. The calculated apparent activation energy and strain rate exponent value were similar to those found for Inconel^®718 when deforming above the solvus temperature. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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17 pages, 4717 KiB

Open AccessArticle

Temperature Resistance of Mo₃Si: Phase Stability, Microhardness, and Creep Properties

by Olha Kauss, Susanne Obert, Iurii Bogomol, Thomas Wablat, Nils Siemensmeyer, Konstantin Naumenko and Manja Krüger

Metals 2021, 11(4), 564; https://doi.org/10.3390/met11040564 - 30 Mar 2021

Cited by 8 | Viewed by 2535

Abstract

Mo-Si-B alloys are one of the most promising candidates to substitute Ni based superalloys in gas turbines. The optimization of their composition can be achieved more effectively using multi-scale modeling of materials behavior and structural analysis of components for understanding, predicting, and screening properties of new alloys. Nevertheless, this approach is dependent on data on the properties of the single phases in these alloys. The focus of this investigation is Mo₃Si, one of the phases in typical Mo-Si-B alloys. The effect of 100 h annealing at 1600 °C on phase stability and microhardness of its three near-stoichiometric compositions—Mo-23Si, Mo-24Si and Mo-25Si (at %)—is reported. While Mo-23Si specimen consist only of Mo₃Si before and after annealing, Mo-24Si and Mo-25Si comprise Mo₅Si₃ and Mo₃Si before annealing. The latter is then increased by the annealing. No significant difference in microhardness was detected between the different compositions as well as after annealing. The creep properties of Mo₃Si are described at 1093 °C and 1300 °C at varying stress levels as well as at 300 MPa and temperatures between 1050 °C and 1350 °C. Three constitutive models were used for regression of experimental results—(i) power law with a constant creep exponent, (ii) stress range dependent law, and (iii) power law with a temperature-dependent creep exponent. It is confirmed that Mo₃Si has a higher creep resistance than Mo_ss and multi-phase Mo-Si-B alloys, but a lower creep strength as compared to Mo₅SiB₂. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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16 pages, 4013 KiB

Open AccessArticle

Effect of Low-Temperature Annealing on Creep Properties of AlSi10Mg Alloy Produced by Additive Manufacturing: Experiments and Modeling

by Chiara Paoletti, Emanuela Cerri, Emanuele Ghio, Eleonora Santecchia, Marcello Cabibbo and Stefano Spigarelli

Metals 2021, 11(2), 179; https://doi.org/10.3390/met11020179 - 20 Jan 2021

Cited by 9 | Viewed by 2268

Abstract

The effects of postprocessing annealing at 225 °C for 2 h on the creep properties of AlSi10Mg alloy were investigated through constant load experiments carried out at 150 °C, 175 °C and 225 °C. In the range of the experimental conditions here considered, the annealing treatment resulted in an increase in minimum creep rate for a given stress. The reduction in creep strength was higher at the lowest temperature, while the effect progressively vanished as temperature increased and/or applied stress decreased. The minimum creep rate dependence on applied stress was modeled using a physically-based model which took into account the ripening of Si particles at high temperature and which had been previously applied to the as-deposited alloy. The model was successfully validated, since it gave an excellent description of the experimental data. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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14 pages, 4278 KiB

Open AccessArticle

High Strain Rate Superplasticity of WE54 Mg Alloy after Severe Friction Stir Processing

by Marta Álvarez-Leal, Fernando Carreño, Alberto Orozco-Caballero, Pilar Rey and Oscar A. Ruano

Metals 2020, 10(12), 1573; https://doi.org/10.3390/met10121573 - 25 Nov 2020

Cited by 9 | Viewed by 1919

Abstract

Friction stir processing (FSP) was used on coarse-grained WE54 magnesium alloy plates of as-received material. These were subjected to FSP under two different cooling conditions, refrigerated and non-refrigerated, and different severe processing conditions characterized by low rotation rate and high traverse speed. After FSP, ultrafine equiaxed grains and refinement of the coarse precipitates were observed. The processed materials exhibited high resistance at room temperature and excellent superplasticity at the high strain rate of 10⁻² s⁻¹ and temperatures between 300 and 400 °C. Maximum tensile superplastic elongation of 726% was achieved at 400 °C. Beyond 400 °C, a noticeable loss of superplastic response occurred due to a loss of thermal stability of the grain size. Grain boundary sliding is the operative deformation mechanism that can explain the high-temperature flow behavior of the ultrafine grained FSP-WE54 alloy, showing increasing superplasticity with increasing processing severity. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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11 pages, 1939 KiB

Open AccessArticle

New Developments in Understanding Harper–Dorn, Five-Power Law Creep and Power-Law Breakdown

by Michael E. Kassner

Metals 2020, 10(10), 1284; https://doi.org/10.3390/met10101284 - 25 Sep 2020

Cited by 7 | Viewed by 2382

Abstract

This paper discusses recent developments in creep, over a wide range of temperature, that may change our understanding of creep. The five-power law creep exponent (3.5–7) has never been explained in fundamental terms. The best the scientific community has done is to develop a natural three power-law creep equation that falls short of rationalizing the higher stress exponents that are typically five. This inability has persisted for many decades. Computational work examining the stress-dependence of the climb rate of edge dislocations may rationalize the phenomenological creep equations. Harper–Dorn creep, “discovered” over 60 years ago, has been immersed in controversy. Some investigators have insisted that a stress exponent of one is reasonable. Others believe that the observation of a stress exponent of one is a consequence of dislocation network frustration. Others believe the stress exponent is artificial due to the inclusion of restoration mechanisms, such as dynamic recrystallization or grain growth that is not of any consequence in the five power-law regime. Also, the experiments in the Harper–Dorn regime, which accumulate strain very slowly (sometimes over a year), may not have attained a true steady state. New theories suggest that the absence or presence of Harper–Dorn may be a consequence of the initial dislocation density. Novel experimental work suggests that power-law breakdown may be a consequence of a supersaturation of vacancies which increase self-diffusion. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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18 pages, 9826 KiB

Open AccessArticle

Hot Deformation Behavior and Processing Map of High-Strength Nickel Brass

by Qiang Liang, Xin Liu, Ping Li and Xianming Zhang

Metals 2020, 10(6), 782; https://doi.org/10.3390/met10060782 - 12 Jun 2020

Cited by 4 | Viewed by 2411

Abstract

The flow behavior of a new kind of high-strength nickel brass used as automobile synchronizer rings was investigated by hot compression tests with a Gleeble-3500 isothermal simulator at strain rates ranging from 0.01 to 10 s⁻¹ and a wide deformation temperature range of 873–1073K at intervals of 50 K. The experimental results show that flow stress increases with increasing strain rate and decreasing deformation temperature, and discontinuous yielding appeared in the flow stress curves at higher strain rates. A modified Arrhenius constitutive model considering the compensation of strain was established to describe the flow behavior of this alloy. A processing map was also constructed with strain of 0.3, 0.6, and 0.9 based on the obtained experimental flow stress–strain data. In addition, the optical microstructure evolution and its connection with the processing map of compressed specimens are discussed. The predominant deformation mechanism of Cu-Ni-Al brass is dynamic recovery when the deformation temperature is lower than 973 K and dynamic recrystallization when the deformation temperature is higher than 973 K according to optical observation. The processing map provides the optimal hot working temperature and strain rate, which is beneficial in choosing technical parameters for this high-strength alloy. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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Review

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25 pages, 6744 KiB

Open AccessReview

Review on Dynamic Recrystallization of Martensitic Stainless Steels during Hot Deformation: Part I—Experimental Study

by Hamed Aghajani Derazkola, Eduardo García Gil, Alberto Murillo-Marrodán and Damien Méresse

Metals 2021, 11(4), 572; https://doi.org/10.3390/met11040572 - 01 Apr 2021

Cited by 35 | Viewed by 4696

Abstract

The evolution of the microstructure changes during hot deformation of high-chromium content of stainless steels (martensitic stainless steels) is reviewed. The microstructural changes taking place under high-temperature conditions and the associated mechanical behaviors are presented. During the continuous dynamic recrystallization (cDRX), the new grains nucleate and growth in materials with high stacking fault energies (SFE). On the other hand, new ultrafine grains could be produced in stainless steel material irrespective of the SFE employing high deformation and temperatures. The gradual transformation results from the dislocation of sub-boundaries created at low strains into ultrafine grains with high angle boundaries at large strains. There is limited information about flow stress and monitoring microstructure changes during the hot forming of martensitic stainless steels. For this reason, continuous dynamic recrystallization (cDRX) is still not entirely understood for these types of metals. Recent studies of the deformation behavior of martensitic stainless steels under thermomechanical conditions investigated the relationship between the microstructural changes and mechanical properties. In this review, grain formation under thermomechanical conditions and dynamic recrystallization behavior of this type of steel during the deformation phase is discussed. Full article

(This article belongs to the Special Issue High-Temperature Behavior of Metals)

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