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Structural Phenomena in Metallic Materials for Demanding Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (10 August 2024) | Viewed by 20004

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Dr. Lenka Kunčická

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Institut of Physics of Materials, Czech Academy of Sciences, Brno, Czech Republic
Interests: thermo-mechanical treatment; non-ferrous metals; structure and stress analyses; numerical methods
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Special Issue Information

Dear Colleagues and Researchers,

The ever-increasing requirements of industry and commerce on the performance and longevity of components produced from metallic materials have encouraged the research and development of innovative engineering materials based on iron/steel and nonferrous metals, as well as metal-based composites. The properties of modern materials and alloys ensue from their structures. Structural phenomena, such as substructure development, volumes and types of grains boundaries, twinning, texture formation, as well as the possible occurrence of residual stress and mutual diffusion of the individual phases, non-negligibly affecting the performance of metallic components, can primarily be affected by their chemical and phase composition, and the applied preparation/production technology.

At the beginning of the production process, the material is affected by the manufacturing method. The selected parameters of casting, additive manufacturing, or powder metallurgy processing all influence the structures and properties of the final material. Among the favorable ways to effectively enhance the properties of metallic materials is also grain refinement, which can advantageously be introduced via plastic deformation. Nonconventional forming technologies, such as severe plastic deformation (SPD) processes, conventional forming processes in combination with thermomechanical treatments, and optimized heat treatments all represent advantageous means to modify the structures of metallic materials in order to significantly improve their performance. Especially the application of optimized modern processing and forming technologies on alloys and compounds featuring innovative chemical compositions can lead to exceptional structure characteristics, providing the final material with superior performance.

It is my pleasure to invite you to submit your scientific manuscripts to the presented Special Issue. Full papers, communications, and reviews are all welcome.

Dr. Lenka Kunčická
Guest Editor

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Keywords

(sub)structure characterization
residual stress
texture
grains and boundaries
precipitation
dislocations
lattice parameters
structure phases
diffusion

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Published Papers (10 papers)

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Research

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22 pages, 8766 KiB

Open AccessArticle

Residual Stress Distribution in Dievar Tool Steel Bars Produced by Conventional Additive Manufacturing and Rotary Swaging Processes

by Josef Izák, Pavel Strunz, Olena Levytska, Gergely Németh, Jan Šaroun, Radim Kocich, Marek Pagáč and Kostyantyn Tuharin

Materials 2024, 17(23), 5706; https://doi.org/10.3390/ma17235706 - 22 Nov 2024

Cited by 2 | Viewed by 1176

Abstract

The impact of manufacturing strategies on the development of residual stresses in Dievar steel is presented. Two fabrication methods were investigated: conventional ingot casting and selective laser melting as an additive manufacturing process. Subsequently, plastic deformation in the form of hot rotary swaging at 900 °C was applied. Residual stresses were measured using neutron diffraction. Microstructural and phase analysis, precipitate characterization, and hardness measurement—carried out to complement the investigation—showed the microstructure improvement by rotary swaging. The study reveals that the manufacturing method has a significant effect on the distribution of residual stresses in the bars. The results showed that conventional ingot casting resulted in low levels of residual stresses (up to ±200 MPa), with an increase in hardness after rotary swaging from 172 HV1 to 613 HV1. SLM-manufactured bars developed tensile hoop and axial residual stresses in the vicinity of the surface and large compressive axial stresses (−600 MPa) in the core due to rapid cooling. The subsequent thermomechanical treatment via rotary swaging effectively reduced both the surface tensile (to approximately +200 MPa) and the core compressive residual stresses (to −300 MPa). Moreover, it resulted in a predominantly hydrostatic stress character and a reduction in von Mises stresses, offering relatively favorable residual stress characteristics and, therefore, a reduction in the risk of material failure. In addition to the significantly improved stress profile, rotary swaging contributed to a fine grain (3–5 µm instead of 10–15 µm for the conventional sample) and increased the hardness of the SLM samples from 560 HV1 to 606 HV1. These insights confirm the utility of rotary swaging as a post-processing technique that not only reduces residual stresses but also improves the microstructural and mechanical properties of additively manufactured components. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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11 pages, 3788 KiB

Open AccessArticle

(Sub)structure Development in Gradually Swaged Electroconductive Bars

by Jaromír Kopeček, Lucia Bajtošová, Petr Veřtát and Daniel Šimek

Materials 2023, 16(15), 5324; https://doi.org/10.3390/ma16155324 - 28 Jul 2023

Cited by 2 | Viewed by 1043

Abstract

Copper generally exhibits high electrical conductivity but has poor mechanical properties. Although alloying can improve the latter characteristic, it usually leads to a decrease in electrical conductivity. To address this issue, a promising approach is to enhance the performance of copper while maintaining high electrical conductivity through optimized deformation processing, which refines the structure and increases mechanical properties. This paper focuses on assessing the effects of rotary swaging, a form of deformation processing, on microstructures and substructures of electroconductive copper bars. This analysis is complemented by experimental measurements of electrical conductivity. The results demonstrate that gradual swaging, i.e., applying different swaging ratios, influences the structure-forming processes and consequently affects the electrical conductivity. The increased electrical conductivity was found to be associated with the elongation of the grains in the direction of the electron movement. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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16 pages, 3616 KiB

Open AccessArticle

Influence of Structure Development on Performance of Copper Composites Processed via Intensive Plastic Deformation

by Radim Kocich, Petr Opěla and Martin Marek

Materials 2023, 16(13), 4780; https://doi.org/10.3390/ma16134780 - 2 Jul 2023

Cited by 4 | Viewed by 1371

Abstract

Designing a composite, possibly strengthened by a dispersion of (fine) oxides, is a favorable way to improve the mechanical characteristics of Cu while maintaining its advantageous electric conductivity. The aim of this study was to perform mechanical alloying of a Cu powder with a powder of Al₂O₃ oxide, seal the powder mixture into evacuated Cu tubular containers, i.e., cans, and apply gradual direct consolidation via rotary swaging at elevated temperatures, as well as at room temperature (final passes) to find the most convenient way to produce the designed Al₂O₃ particle-strengthened Cu composite. The composites swaged with the total swaging degree of 1.83 to consolidated rods with a diameter of 10 mm were subjected to measurements of electroconductivity, investigations of mechanical behavior via compression testing, and detailed microstructure observations. The results revealed that the applied swaging degree was sufficient to fully consolidate the canned powders, even at moderate and ambient temperatures. In other words, the final structures, featuring ultra-fine grains, did not exhibit voids or remnants of unconsolidated powder particles. The swaged composites featured favorable plasticity regardless of the selected processing route. The flow stress curves exhibited the establishment of steady states with increasing strain, regardless of the applied strain rate. The electroconductivity of the composite swaged at elevated temperatures, featuring homogeneous distribution of strengthening oxide particles and the average grain size of 1.8 µm², reaching 80% IACS (International Annealed Copper Standard). Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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16 pages, 3929 KiB

Open AccessArticle

Optimizing Thermomechanical Processing of Bimetallic Laminates

by Radim Kocich

Materials 2023, 16(9), 3480; https://doi.org/10.3390/ma16093480 - 30 Apr 2023

Cited by 3 | Viewed by 1733

Abstract

Thermomechanical processing combining plastic deformation and heat treatment is a favorable way to enhance the performance and lifetime of bimetallic laminates, especially those consisting of metals, which tend to form intermetallic layers on the interfaces when produced using methods involving increased temperatures. The presented work focuses on optimizing the conditions of thermomechanical treatment for an Al + Cu bimetallic laminate of innovative design involving a shear-strain-based deformation procedure (rotary swaging) and post-process heat treatment in order to acquire microstructures providing advantageous characteristics during the transfer of direct and alternate electric currents. The specific electric resistivity, as well as microhardness, was particularly affected by the structural features, e.g., grain size, the types of grain boundaries, and grain orientations, which were closely related to the applied thermomechanical procedure. The microhardness increased considerably after swaging (up to 116 HV02 for the Cu components), but it decreased after the subsequent heat treatment at 350 °C. Nevertheless, the heat-treated laminates still featured increased mechanical properties. The measured electric characteristics for DC transfer were the most favorable for the heat-treated 15 mm bimetallic laminate featuring the lowest measured specific electric resistivity of 22.70 × 10⁻⁹ Ωm, while the 10 mm bimetallic laminates exhibited advantageous behavior during AC transfer due to a very low power loss coefficient of 1.001. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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21 pages, 9262 KiB

Open AccessArticle

High Cycle Fatigue Behaviour of 316L Stainless Steel Produced via Selective Laser Melting Method and Post Processed by Hot Rotary Swaging

by Petr Opěla, Marek Benč, Stepan Kolomy, Zdeněk Jakůbek and Denisa Beranová

Materials 2023, 16(9), 3400; https://doi.org/10.3390/ma16093400 - 26 Apr 2023

Cited by 8 | Viewed by 2460

Abstract

This paper deals with a study of additively manufactured (by the Selective Laser Melting, SLM, method) and conventionally produced AISI 316L stainless steel and their comparison. With the intention to enhance the performance of the workpieces, each material was post-processed via hot rotary swaging under a temperature of 900 °C. The samples of each particular material were analysed regarding porosity, microhardness, high cycle fatigue, and microstructure. The obtained data has shown a significant reduction in the residual porosity and the microhardness increase to 310 HV in the sample after the hot rotary swaging. Based on the acquired data, the sample produced via SLM and post-processed by hot rotary swaging featured higher fatigue resistance compared to conventionally produced samples where the stress was set to 540 MPa. The structure of the printed samples changed from the characteristic melting pools to a structure with a lower average grain size accompanied by a decrease of a high fraction of high-angle grain boundaries and higher geometrically necessary dislocation density. Specifically, the grain size decreased from the average diameters of more than 20 µm to 3.9 µm and 4.1 µm for the SLM and conventionally prepared samples, respectively. In addition, the presented research has brought in the material constants of the Hensel-Spittel formula adapted to predict the hot flow stress evolution of the studied steel with respect to its 3D printed state. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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13 pages, 2789 KiB

Open AccessArticle

High Pressure Torsion of Copper; Effect of Processing Temperature on Structural Features, Microhardness and Electric Conductivity

by Lenka Kunčická, Michal Jambor and Petr Král

Materials 2023, 16(7), 2738; https://doi.org/10.3390/ma16072738 - 29 Mar 2023

Cited by 5 | Viewed by 1930

Abstract

By optimizing the fabrication method, copper components featuring (typically contradicting) advantageous electric conductivity and favorable mechanical properties can be acquired. In this study, we subjected conventional electroconductive copper to a single revolution of high pressure torsion (HPT) at room temperature (RT), searched for the conditions which would yield comparable structure characteristics (grain size) when deformed at a cryogenic temperature, and finally compared the mechanical and electric behaviors to assess specific differences and correlate them with the (sub)structural development. 180° revolution of cryo-HPT imparted structure refinement comparable to 360° revolution of room temperature HPT, i.e., the average grain size at the periphery of both the specimens was ~7 µm. The 360° RT HPT specimen exhibited preferential (111)||SD (shear direction) texture fiber in all the examined regions, whereas the 180° cryo-HPT specimen exhibited more or less randomly oriented grains of equiaxed shapes featuring substantial substructure development of a relatively homogeneous character and massive occurrence of (nano)twins. These structural features resulted in the increase in microhardness to the average value of 118.2 HV0.2 and the increase in the electric conductivity to 59.66 MS·m⁻¹ (compared to 105 HV0.2 and 59.14 MS·m⁻¹ acquired for the 360° RT HPT specimen). The deformation under the cryogenic conditions also imparted higher homogeneity of microhardness distribution when compared to RT processing. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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21 pages, 7531 KiB

Open AccessArticle

Residual Stress Distribution in a Copper-Aluminum Multifilament Composite Fabricated by Rotary Swaging

by David Canelo-Yubero, Radim Kocich, Jan Šaroun and Pavel Strunz

Materials 2023, 16(5), 2102; https://doi.org/10.3390/ma16052102 - 5 Mar 2023

Cited by 6 | Viewed by 2134

Abstract

Rotary swaging is a promising technique for the fabrication of clad Cu/Al composites. Residual stresses appearing during the processing of a special arrangement of Al filaments within the Cu matrix and the influence of the bar reversal between the passes were studied by (i) neutron diffraction using a novel evaluation procedure for pseudo-strain correction and (ii) a finite element method simulation. The initial study of the stress differences in the Cu phase allowed us to infer that the stresses around the central Al filament are hydrostatic when the sample is reversed during the passes. This fact enabled the calculation of the stress-free reference and, consequently, the analysis of the hydrostatic and deviatoric components. Finally, the stresses with the von Mises relation were calculated. Hydrostatic stresses (far from the filaments) and axial deviatoric stresses are zero or compressive for both reversed and non-reversed samples. The reversal of the bar direction slightly changes the overall state within the region of high density of Al filaments, where hydrostatic stresses tend to be tensile, but it seems to be advantageous for avoiding plastification in the regions without Al wires. The finite element analysis revealed the presence of shear stresses; nevertheless, stresses calculated with the von Mises relation show similar trends in the simulation and in the neutron measurements. Microstresses are suggested as a possible reason for the large width of the neutron diffraction peak in the measurement of the radial direction. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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18 pages, 6462 KiB

Open AccessArticle

Dilatation of New Progressive Hybrid Sand and Its Effect on Surface Structure, Roughness, and Veining Creation within Grey Cast Iron

by Martina Bašistová, Filip Radkovský, Ivana Kroupová and Petr Lichý

Materials 2023, 16(5), 2004; https://doi.org/10.3390/ma16052004 - 28 Feb 2023

Cited by 3 | Viewed by 1655

Abstract

The constant effort of all metal alloy manufacturing technologies and processes is to improve the resulting quality of the processed part. Not only the metallographic structure of the material is monitored, but also the final quality of the cast surface. In foundry technologies, in addition to the quality of the liquid metal, external influences, such as the behaviour of the mould or core material, significantly affect the cast surface quality. As the core is heated during casting, the resulting dilatations often lead to significant volume changes causing stress foundry defects such as veining, penetration and surface roughness. In the experiment, various amounts of silica sand were replaced with artificial sand and a significant reduction in dilation and pitting of up to 52.9% was observed. An important finding was the effect of the granulometric composition and grain size of the sand on the formation of surface defects from brake thermal stresses. The specific mixture composition can be considered as an effective prevention against the formation of defects instead of using a protective coating. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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18 pages, 46859 KiB

Open AccessArticle

Influence of Aging Temperature on Mechanical Properties and Structure of M300 Maraging Steel Produced by Selective Laser Melting

by Stepan Kolomy, Josef Sedlak, Jan Zouhar, Martin Slany, Marek Benc, David Dobrocky, Igor Barenyi and Jozef Majerik

Materials 2023, 16(3), 977; https://doi.org/10.3390/ma16030977 - 20 Jan 2023

Cited by 12 | Viewed by 2773

Abstract

This paper deals with the study of high-strength M300 maraging steel produced using the selective laser melting method. Heat treatment consists of solution annealing and subsequent aging; the influence of the selected aging temperatures on the final mechanical properties—microhardness and compressive yield strength—and the structure of the maraging steel are described in detail. The microstructure of the samples is examined using optical and electron microscopy. The compressive test results show that the compressive yield strength increased after heat treatment up to a treatment temperature of 480 °C and then gradually decreased. The sample aged at 480 °C also exhibited the highest observed microhardness of 562 HV. The structure of this sample changed from the original melt pools to a relatively fine-grained structure with a high fraction of high-angle grain boundaries (72%). Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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Review

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21 pages, 5171 KiB

Open AccessReview

Structural Phenomena Introduced by Rotary Swaging: A Review

by Lenka Kunčická

Materials 2024, 17(2), 466; https://doi.org/10.3390/ma17020466 - 18 Jan 2024

Cited by 4 | Viewed by 2173

Abstract

Rotary swaging is an industrially applicable intensive plastic deformation method. Due to its versatility, it is popular, especially in the automotive industry. Similar to the well-known methods of severe plastic deformation (SPD), rotary swaging imparts high shear strain into the swaged materials and thus introduces grain refinement down to a very fine, even ultra-fine, level. However, contrary to SPD methods, one of the primary characteristics of which is that they retain the shapes and dimensions of the processed sample, rotary swaging enables the imparting of required shapes and dimensions of workpieces (besides introducing structure refinement and the consequent enhancement of properties and performance). Therefore, under optimized conditions, swaging can be used to process workpieces of virtually any metallic material with theoretically any required dimensions. The main aim of this review is to present the principle of the rotary swaging method and its undeniable advantages. The focus is primarily on assessing its pros and cons by evaluating the imparted microstructures. Full article

(This article belongs to the Special Issue Structural Phenomena in Metallic Materials for Demanding Applications)

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