Special Issue "Strengthening Mechanisms in Metallic Materials"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 30 June 2020.

Special Issue Editor

Dr. Andrii Kostryzhev
E-Mail Website
Guest Editor
School of Mechanical, Materials, Mechatronic and Biomedical Engineering, University of Wollongong, NSW 2500, Australia
Interests: alloy chemistry; processing technology; phase transformations; microstructure characterization; microscopy; strengthening mechanisms; mechanical properties

Special Issue Information

Dear Colleagues,

The mechanical properties of contemporary engineering alloys are reaching their natural limits, despite the fact that the growing human population and transportation networks, energy shortage and ecological problems require even stronger, tougher and lighter alloys, with an extended application temperature range. The mechanical properties originate from the alloy composition and processing history and through the microstructure development. Quite often, a successful processing technology was designed to utilize a particular strengthening mechanism: grain refinement, phase balance, precipitation or solid solution strengthening. This could be determined by particular product requirements, the available equipment, cost, or company tradition. However, new challenges for further property enhancement require a review of the capacity of strengthening mechanisms. Are the precipitates more effective than solute atoms? What is the most reasonable size of grains in a polycrystalline alloy? What state of dislocation structure is required and what criteria define this? How many phases of microstructure do we need? Will the multi-principle element alloys become the future of alloy chemistry? Will the rolling and forging disappear, and will casting, powder pressing and 3D printing dominate in the technology space? Research articles, communications or reviews on these questions are very welcome to this Special Issue, irrespective of alloy composition or processing technology. Feel free to put forward your challenges. Let us discuss the role of strengthening mechanisms in view of their influence on alloy chemistry and technology design.

Dr. Andrii Kostryzhev
Guest Editor

Manuscript Submission Information

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Keywords

  • alloy chemistry
  • processing technology
  • microstructure characterization
  • testing of mechanical properties
  • microstructure–properties relationship

Published Papers (8 papers)

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Research

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Open AccessArticle
Analysis of the Bauschinger Effect in Cold Drawn Pearlitic Steels
Metals 2020, 10(1), 114; https://doi.org/10.3390/met10010114 - 12 Jan 2020
Abstract
Prestressing steel wires usually undergo cyclic loading in service. Therefore, it is of interest to analyse certain features of their mechanical behaviour under this type of loading, such as the Bauschinger effect (BE) or the hardening rule, that fit the real mechanical behaviour [...] Read more.
Prestressing steel wires usually undergo cyclic loading in service. Therefore, it is of interest to analyse certain features of their mechanical behaviour under this type of loading, such as the Bauschinger effect (BE) or the hardening rule, that fit the real mechanical behaviour appropriately. In this study, different samples of high strength pearlitic steel wires were subjected to cyclic tension-compression load exceeding the material yield strength, thus generating plastic strains. From the experimental results, various parameters were obtained revealing that analysed steels exhibited the so-called Masing type BE. In addition, the variation of the BE characteristics (of the effective and internal stresses) with the applied plastic pre-strain indicated that the studied materials followed a mixed strain hardening rule with the domination of the kinematic component. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
Open AccessArticle
Production of Surface Layer with Gradient Microstructure and Microhardess on Copper by High Pressure Surface Rolling
Metals 2020, 10(1), 73; https://doi.org/10.3390/met10010073 - 02 Jan 2020
Abstract
Pure copper was subjected to high-pressure surface rolling (HPSR) to obtain a surface gradient layer. Effects of HPSR parameters on the surface microstructure and microhardness of Cu were investigated by using optical microscopy, transmission electronic microscopy, X-ray diffraction, and the microhardness test. The [...] Read more.
Pure copper was subjected to high-pressure surface rolling (HPSR) to obtain a surface gradient layer. Effects of HPSR parameters on the surface microstructure and microhardness of Cu were investigated by using optical microscopy, transmission electronic microscopy, X-ray diffraction, and the microhardness test. The HPSR surface layer has a gradient microstructure consisting of increasingly refined grains with decreasing depth from the treated surface (DFS). The thicknesses of the refined surface layer can be up to ~1.8 mm, and the grain size of the topmost surface is down to ~88 nm, depending on the HPSR parameters including pressure, time, and temperature. Microhardness of HPSR samples increases with decreasing DFS, with a maximum of ~2.4 times that of the undeformed matrix. The present results indicated that HPSR could be an effective method for the production of a mm-thick surface layer on Cu with gradient microstructure and property. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
Influence of Tempering Time on the Behavior of Large Carbides’ Coarsening in AISI H13 Steel
Metals 2019, 9(12), 1283; https://doi.org/10.3390/met9121283 - 29 Nov 2019
Abstract
The mechanical properties, microstructures and precipitation behaviors in AISI (American Iron and Steel Institute) H13 steel tempered at 863 K for 0.5, 2, 4, 10 and 20 h were investigated. The values for H13 tempered for 2–4 h resulted in die steel that [...] Read more.
The mechanical properties, microstructures and precipitation behaviors in AISI (American Iron and Steel Institute) H13 steel tempered at 863 K for 0.5, 2, 4, 10 and 20 h were investigated. The values for H13 tempered for 2–4 h resulted in die steel that reached the desired properties as specified in NADCA (North American Die Casting Association) #207-2016. The cubic Ostwald ripening model was applied to simulate the coarsening of the large carbides, which were mainly M23C6 and M3C, as determined from FactSage predictions as well as measurements with transmission electron microscopy (TEM). TEM revealed that the equivalent circle radius (ECR) decreased during 0.5–2 h, because of the nucleation of many new precipitates. According to the Ashby-Orowan modified precipitation strengthening model, this decrease in ECR leads to an increase in the contribution of precipitates to yield strength. Between 2 and 4 h tempering, the ECR of large carbides increases sharply but then increases asymptotically from 4 to 20 h, which obeys the calculated Ostwald ripening rate for cementite and M23C6 in H13 after 863 K tempering. This observation for the Ostwald ripening of M23C6 is in agreement with experimental data for other steels in the literature. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
Effect of Strengthening Methods on the Defect Evolution under Irradiations Investigated with Rate Theory Simulations
Metals 2019, 9(7), 735; https://doi.org/10.3390/met9070735 - 29 Jun 2019
Cited by 1
Abstract
Under irradiations, mechanical performance of nuclear alloys would degrade due to irradiation induced defects. Different strengthening methods can play a different role in the evolution of the defects. In this study, the effect of four typical strengthening methods including fine grain strengthening, dislocation [...] Read more.
Under irradiations, mechanical performance of nuclear alloys would degrade due to irradiation induced defects. Different strengthening methods can play a different role in the evolution of the defects. In this study, the effect of four typical strengthening methods including fine grain strengthening, dislocation strengthening, second phase strengthening and solid solutions strengthening on the defect evolutions in bcc iron-based alloys are investigated with rate theory simulations, a technique capable of simulating a long-term evolution of defects caused by irradiations. Simulations show that at high dose, irradiation induced voids become the dominating factor that affect irradiation hardening. Strengthening methods with the enhancement of sink strength (fine grain strengthening, dislocation strengthening and second phase strengthening) have little effects on the evolution of voids, while strengthening method with impediment of migration of defects (solid solutions strengthening) can effectively inhibit the nucleation and growth of voids. For fine grain strengthening and dislocation strengthening, the irradiation hardening is almost kept unchanged when changing grain size and initial dislocation density. For second phase strengthening, the irradiation hardening can be inhibited to some extent by increasing mainly the number density of precipitates. The solid solutions strengthening is the most proper method to inhibit irradiation hardening of bcc iron-based alloy because it can inhibit the development of voids, especially at high dose. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
Precipitation Strengthening in Ni–Cu Alloys Fabricated Using Wire Arc Additive Manufacturing Technology
Metals 2019, 9(1), 105; https://doi.org/10.3390/met9010105 - 21 Jan 2019
Abstract
Two Ni–Cu alloys, Monel K500 and FM60, with various contents of Ti, Mn, Al, Fe and C were deposited in the form of plates on a metal base plate using wire arc additive manufacturing technology. Three deposition speeds have been applied: 300, 400 [...] Read more.
Two Ni–Cu alloys, Monel K500 and FM60, with various contents of Ti, Mn, Al, Fe and C were deposited in the form of plates on a metal base plate using wire arc additive manufacturing technology. Three deposition speeds have been applied: 300, 400 and 500 mm/min. To modify the as-welded microstructure and properties, the deposited walls/plates have been subjected to two heat treatment procedures: annealing at 1100 °C for 15 min, slow cooling to 610 °C, ageing at this temperature for 8 h and either (i) air cooling to room temperature or (ii) slow cooling to 480 °C, ageing at this temperature for 8 h and air cooling to room temperature. The microstructure characterisation and mechanical properties testing have been conducted for each of the 18 chemistry/processing conditions. The dependences of the precipitate’s parameters (size, number density and chemistry), mechanical properties and wear resistance on the alloy composition, deposition speed and heat treatment have been obtained. In Monel K500, the precipitates were mainly of the TiC/TiCN type, and in FM60, they were of the MnS and TiAlMgO types. Monel K500 has shown higher hardness, strength, toughness and wear resistance in all studied conditions. Ageing at 610 °C improved properties in both alloys following the precipitation of new particles. Ageing at 480 °C could result in a properties loss if the particle coarsening (decrease in number density) took place. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
Effect of T6 Heat Treatment on Microstructure and Hardness of Nanosized Al2O3 Reinforced 7075 Aluminum Matrix Composites
Metals 2019, 9(1), 44; https://doi.org/10.3390/met9010044 - 05 Jan 2019
Cited by 1
Abstract
In this study, 7075 aluminum matrix composites reinforced with 1.5 wt.% nanosized Al2O3 were fabricated by ultrasonic vibration. The effect of T6 heat treatment on both microstructure and hardness of nanosized Al2O3 reinforced 7075 (Al2O [...] Read more.
In this study, 7075 aluminum matrix composites reinforced with 1.5 wt.% nanosized Al2O3 were fabricated by ultrasonic vibration. The effect of T6 heat treatment on both microstructure and hardness of nanosized Al2O3 reinforced 7075 (Al2O3np/7075) composites were studied via scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, and hardness tests. The Mg(Zn,Cu,Al)2 phases gradually dissolved into the matrix under solution treatment at 480 °C for 5 h. However, the morphology and size of Al7Cu2Fe phases remained unchanged due to their high melting points. Furthermore, the slenderness strips MgZn2 phases precipitated under aging treatment at 120 °C for 24 h. Compared to as-cast composites, the hardness of the sample under T6 heat treatment was increased ~52%. The strengthening mechanisms underlying the achieved hardness of composites are revealed. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
Microstructure, Mechanical Properties and Strengthening Mechanism Analysis in an AlMg5 Aluminium Alloy Processed by ECAP and Subsequent Ageing
Metals 2018, 8(11), 969; https://doi.org/10.3390/met8110969 - 20 Nov 2018
Cited by 6
Abstract
A coarse-grained microstructure of solution treated AlMg5 aluminium alloy was prepared by equal channel angular pressing through route BC. Microstructure evolution of the alloy was analysed by using an optical microscope, X-ray diffraction, and EBSD (electron backscatter diffraction). The results reported [...] Read more.
A coarse-grained microstructure of solution treated AlMg5 aluminium alloy was prepared by equal channel angular pressing through route BC. Microstructure evolution of the alloy was analysed by using an optical microscope, X-ray diffraction, and EBSD (electron backscatter diffraction). The results reported that grains were refined due to the interactions of shear bands with low-to-moderate grain boundaries, and this structure was transformed into a bimodal after ageing at 180 °C for 4 h. Moreover, the results of the tensile testing showed that the yield strength was increased from 110 to 326 MPa, and the corresponding tensile strength increased from 269 to 395 MPa, maintaining an appropriate elongation of ~18%. After ageing at 180 °C elongation increased to 23% and the sample still kept high yield strength of 255 MPa, which may be associated with the mutual influence of the dislocation density decrease and recrystallization processes. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Review

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Open AccessReview
A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals
Metals 2019, 9(5), 598; https://doi.org/10.3390/met9050598 - 24 May 2019
Abstract
Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures [...] Read more.
Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures in metals have been proven to be a new strategy to achieve unprecedented mechanical properties that are not accessible to their homogeneous counterparts. Here, we review recent advances in overcoming this strength–ductility trade-off by the designs of several heterogeneous nanostructures in metals: heterogeneous grain/lamellar/phase structures, gradient structure, nanotwinned structure and structure with nanoprecipitates. These structural heterogeneities can induce stress/strain partitioning between domains with dramatically different strengths, strain gradients and geometrically necessary dislocations near domain interfaces, and back-stress strengthening/hardening for high strength and large ductility. This review also provides the guideline for optimizing the mechanical properties in heterogeneous nanostructures by highlighting future challenges and opportunities. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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