Bulk Ultrafine-grained Materials Research Articles

Fabrication of ultrafine-grained Cu-Mn alloy with uniform microstructure and high mechanical properties

Homogenization, random orientation, and high strength are the research goals of target materials. In this study, the bulk ultrafine-grained (UFG) Cu-5Mn alloy target materials were prepared by two typical severe plastic deformation methods, equal channel angular pressing (ECAP) and auxiliary-cooling multi-pass friction stir processing (MPFSP), and their structure-property relationships were comparatively investigated. Compared to the ECAP sample with extremely heterogeneous microstructure, the MPFSP sample exhibited finer and more uniform equiaxed microstructure with weaker texture and higher tensile strength of 614 MPa, which was consistent with the requirements of an ideal target material. This study provides a new perspective on the optimization of target materials.

Development and study of combined severe plastic deformation process

To increase the level of accumulated deformations during angular pressing, known routes are used, based on inter-transitional rotation of the workpiece at a certain angle before the next installation in a stamp. With the advent of relatively new methods for obtaining of bulk ultrafine-grained materials, the possibility of combining angular pressing and its rotation in accordance with a given route in one pass of the workpiece through intersecting channels of the die in accordance with a given route is studied, for which a technological process is developed and studied, in which equal-channel angular pressing and screw extrusion are combined. The computer simulation of the proposed process made it possible to reveal the features of the kinematics of the flow in the channels of the die, to predict the values of the contact pressure, power parameters and the resulting stresses and accumulated deformations in the volume of the pressed billet.

Effect of stress-strain curve changing with equal channel angular pressing on ultimate strength of ship hull stiffened panels

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 um (initial grain size was 25 um) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

A review on SPD processes used to produce ultrafine-grained and multilayer nanostructured tubes

During the many years, severe plastic deformation study carried out based on processes appropriate for sheet and solid materials. However, the review to study the SPD methods suitable for nanostructure tube yet not done. So, efforts have been put to review and develop effective SPD processes suitable for producing cylindrical tubes. Severe plastic deformation is recognized to be the paramount technique for manufacturing bulk ultrafine-grained and nanostructured materials with high strength and hardness. The present study is about the state-of-the-art review on different SPD methods suitable to produce ultrafine-grained and multilayer nanostructured tubes. This study also reveals the impact of various tube SPD methods on the material properties of the tube. The comparison between them based on the advantages and disadvantages of SPD techniques are done based on the viewpoints of processing and properties. Also, find out the literature review gap for a more detail study on a multilayer nanostructured tube.

A novel method for preparing bulk ultrafine-grained material: Three dimensional severe plastic deformation

A novel severe plastic deformation method entitled three dimensional severe plastic deformation was proposed for producing bulk ultrafine-grained materials with industry size. Experiment results of 20MnSiV steel indicate that the ferrite was refined to less than 3 μm after single pass 3D-SPD at 650 °C. The yield strength, ultimate tensile strength and elongation are 491.15 MPa, 626.29 MPa and 20.82%, respectively, which are increased by 28.39%, 3.56% and 10.39% as compared with the received sample. The increase in strength and elongation is related to the grain refinement of ferrite and the hindering effect of spheroidized cementite on dislocations.

Correction to: Producing Bulk Ultrafine-Grained Materials by Severe Plastic Deformation

Michael J. Zehetbauer’s name appears incorrectly in the original electronic version of this article. It has been corrected here.

Prediction of Shortening and Material Grain Size after Extrusion Using the ECAP Method

Equal channel angular pressing (ECAP) is a widespread severe plastic deformation (SPD) method to fabricate ultrafine-grained bulk materials. In the field of materials engineering, this method has already experienced rapid development over the past few decades. In this research, the authors sought to create a prediction of shortening and the material particle size after extrusion using ECAP. Behaviours of essential functions are analysed here on samples of pure copper Cu 99.9. It is the measurement and analytical processing of changes in the values of selected structural and mechanical parameters depending on the reduction of the structural granularity. Parameters such as deformation speed, deformation work and ECAP mechanical performance are also included in the results. The change in structure and mechanical parameters is also newly demonstrated by measuring the change in the velocity of the longitudinal ultrasound wave during the experimental passes. Based on the results obtained, new computational algorithms for Excel and Matlab were developed. The algorithms developed here contain many new findings, conclusions and derivations addressing the integrity of the surface with the inner structure of materials. Algorithms are very well-suited for obtaining results on different materials quickly, for predicting and checking measured values, and for designing optimal measurement technology parameters for the ECAP method.

Microstructures and Hardness Prediction of an Ultrafine-Grained Al-2024 Alloy

High-pressure torsion (HPT) is a high efficiency processing method for fabricating bulk ultrafine-grained metallic materials. This work investigates microstructures and evaluates the corresponding strengthening components in the center of HPT disks, where effective shear strains are very low. An Al-4.63Cu-1.51Mg (wt. %) alloy was processed by HPT for 5 rotations. Non-equilibrium grain and sub-grain boundaries were observed using scanning transmission electron microscopy in the center area of HPT disks. Solute co-cluster segregation at grain boundaries was found by energy dispersive spectrometry. Quantitative analysis of X-ray diffraction patterns showed that the average microstrain, crystalline size, and dislocation density were (1.32 ± 0.07) × 10−3, 61.9 ± 1.4 nm, and (2.58 ± 0.07) × 1014 m−2, respectively. The ultra-high average hardness increment was predicted on multiple mechanisms due to ultra-high dislocation densities, grain refinement, and co-cluster–defect complexes.

Evolution of microstructure and hardness in aluminum processed by High Pressure Torsion Extrusion

An investigation was conducted on aluminum samples (AA1050) to study the microstructure and hardness evolution during processing by High Pressure Torsion Extrusion (HPTE). The equivalent strain accumulated in the samples after one pass of HPTE varied in a wide range between 0.9 and 65.5, depending on the processing parameters. HPTE led to the formation of a gradient microstructure in which the grain size decreased by increasing the distance from the central axis of the billets. This gradient decreased significantly by increasing the ratio of rotational speed to extrusion speed. Most of the grain refinement and hardness-increase occurred up to the equivalent strain of ~5 but saturation level was achieved at the strain of ~20. Saturation levels in grain size and hardness were ~0.7 μm and ~67 HV, respectively. HPTE technique can provide similar saturation in microstructure and hardness as those obtained by HPT but in much larger samples. Therefore, HPTE can be a named as a suitable candidate for practical applications to produce bulk ultrafine-grained materials with considerable enhancement in hardness.

Structural Change in Ni-Fe-Ga Magnetic Shape Memory Alloys after Severe Plastic Deformation.

Severe plastic deformation (SPD) is widely considered to be the most efficient process in obtaining ultrafine-grained bulk materials. The aim of this study is to examine the effects of the SPD process on Ni-Fe-Ga ferromagnetic shape memory alloys (FSMA). High-speed high-pressure torsion (HSHPT) was applied in the as-cast state. The exerted key parameters of deformation are described. Microstructural changes, including morphology that were the result of processing, were investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to study the two-phase microstructure of the alloys. The influence of deformation on microstructural features, such as martensitic plates, intragranular γ phase precipitates, and grain boundaries’ dependence of the extent of deformation is disclosed by transmission electron microscopy. Moreover, the work brings to light the influence of deformation on the characteristics of martensitic transformation (MT). Vickers hardness measurements were carried out on disks obtained by SPD so as to correlate the hardness with the microstructure. The method represents a feasible alternative to obtain ultrafine-grained bulk Ni-Fe-Ga alloys.

Micro-Scale Mechanical Behavior of Ultrafine-Grained Materials Processed by High-Pressure Torsion

Bulk ultrafine-grained (UFG) materials usually show superior mechanical and physical properties. The development of micro-mechanical behavior is observed after significant changes in microstructure through high-pressure torsion (HPT) processing. This report summarizes recent results on the evolution of small-scale mechanical response examined by the nanoindentation technique on two UFG materials including a high-entropy alloy and an Al-Mg metal matrix nanocomposite processed by HPT. Special emphasis is placed on demonstrating the interrelationship of essential microstructural changes with increasing torsional strain and applying a post-deformation annealing treatment and the evolution of the micro-mechanical behavior in these UFG materials by estimating the strain rate sensitivity.

Superplastic Flow and Micro-Mechanical Response of Ultrafine-Grained Materials

The bulk ultrafine-grained (UFG) materials usually show superior mechanical properties. Since the occurrence of superplastic flow generally requires a grain size smaller than ~10 μm, it is anticipated that materials processed by severe plastic deformation (SPD) will exhibit superplastic ductilities when pulled in tension at elevated temperatures. Recent advances in the processing of UFG metals have provided an opportunity to extend the understanding of superplastic flow behavior to include UFG materials with submicrometer grain sizes. Recent studies showed the UFG materials demonstrated the development of plasticity in micro-mechanical response at room temperature by the significant changes in microstructure attributed to high-pressure torsion (HPT). Accordingly, this study summarizes recent results on excellent ductility and plasticity in a UFG Zn-22% Al alloy. Specifically, the alloy demonstrated the occurrence of exceptional superplastic flow at high temperature after equal-channel angular pressing and HPT and excellent room temperature plasticity of the alloy after HPT where the plasticity was evaluated by the nanoindentation technique. The significance of purity of the alloy is also considered for enhancing the ductility at room temperature.

7th International Conference on Nanomaterials by Severe Plastic Deformation

Severe plastic deformation (SPD) has arguably been the most effective top-down approach to producing bulk nanostructured materials from more conventional, coarse-grained ones. During SPD processing, a giant shear deformation of a material is combined with very high hydrostatic pressure to produce ultrafine (< 1 μm) or nanocrystalline (< 100 nm) grain structure. Despite the huge strain involved, popular SPD techniques practically do not change the dimensions of a work-piece, which makes them very attractive for future industry-scale applications. By appropriately choosing SPD processing parameters that give rise to desirable microstructure, one can produce materials with exceptional mechanical properties and in many cases unusual functional characteristics.A series of international events briefly referred to as NanoSPD conferences have become major forums for the growing community of researchers exploring the potential of severe plastic deformation as a means of producing bulk ultrafine-grained or nanostructured materials. The 7th International Conference on Nanomaterials by Severe Plastic Deformation in Sydney (2-7 July 2017) is the seventh in this series of conferences held on a triennial basis. It follows the conferences that took place in Moscow (1999), Vienna (2002), Fukuoka (2005), Goslar (2008), Nanjing (2011), and Metz (2014). NanoSPD conferences have provided an important platform for discussion of a wealth of challenging scientific problems and new technological developments in the NanoSPD area. These Proceedings contain a selection of peer-reviewed papers presented at NanoSPD7 that cover the major themes of the conference. These include SPD processing techniques as well as microstructures, deformation mechanisms and properties of SPD-processed materials. Naturally, mechanical properties figure in the Proceedings most prominently, but functional properties, including biodegradation and biocompatibility, are represented as well. A number of articles are dedicated to modelling of SPD processes and the mechanical behaviour of bulk nanostructured materials. A historical perspective and a survey of the most important developments in the field since the NanoSPD6 conference in Metz as well as the emerging industry-scale applications of SPD-modified materials are given in an introductory article by R.Z. Valiev and T.G. Langdon.We would like to thank all those who contributed to the success of NanoSPD7. These include all conference participants, and especially the authors of the papers collected in these Proceedings, the International NanoSPD Steering Committee (www.nanospd.org), the Local Organising Committee (www.nanospd7.com), staff from ICMS Australasia Pty Ltd, and student helpers. We also appreciate the generous financial support from the conference sponsors.

Microstructure and mechanical properties of friction stir processed Cu with an ideal ultrafine-grained structure

Ultrafine-grained (UFG) Cu with uniform microstructure was successfully prepared by friction stir processing (FSP) under additional water cooling. FSP Cu exhibited equiaxed grains with low dislocation density, weak texture, and high fraction of high-angle grain boundaries. Isotropy and tension-compression symmetry were achieved in FSP Cu sample, which provided an ideal model material to investigate the intrinsic mechanical behavior of the UFG material. Enhanced strain hardening was achieved in FSP Cu due to the special microstructure which was effective in accumulating dislocations, resulting in good strength-ductility synergy. This study provides a feasible strategy of preparing bulk UFG materials with good mechanical properties.

Texture evolution and mechanical behavior of commercially pure Ti processed via pulsed electric current treatment

Spark plasma sintering is commonly utilized as a powder consolidation approach to fabricate high-performance ultrafine-grained bulk materials. In this study, a pulsed electric current, generated via spark plasma sintering, was applied to hot-rolled CP-Ti TA1 in order to study the influence on the α↔β allotropic transformation. Results show that an increased grain size of the α-Ti phase, together with a weakened texture, is accompanied by the increased plastic strain in the as-treated TA1 with increasing pulsed electric current intensity. The microstructure and texture changes are attributed to an enhancement in long-range atomic diffusion induced by the pulsed electric current intensity. Concomitantly, the increased plastic strain results from an increase in the number of active slip systems along the direction of the tensile test induced by the weakened texture of the {0001} pole figures and the trend of turning to the direction of the tensile test for the orientation index $$ \left\langle {10\overline{1} 0} \right\rangle $$ in pole figures. The results obtained herein provide an alternative pathway for the fabrication of high-performance metallic materials.

Producing Bulk Ultrafine-Grained Materials by Severe Plastic Deformation: Ten Years Later

It is now well established that the processing of bulk solids through the application of severe plastic deformation (SPD) leads to exceptional grain refinement to the submicrometer or nanometer level. Extensive research over the last decade has demonstrated that SPD processing also produces unusual phase transformations and leads to the introduction of a range of nanostructural features, including nonequilibrium grain boundaries, deformation twins, dislocation substructures, vacancy agglomerates, and solute segregation and clustering. These many structural changes provide new opportunities for fine tuning the characteristics of SPD metals to attain major improvements in their physical, mechanical, chemical, and functional properties. This review provides a summary of some of these recent developments. Special emphasis is placed on the use of SPD processing in achieving increased electrical conductivity, superconductivity, and thermoelectricity, an improved hydrogen storage capability, materials for use in biomedical applications, and the fabrication of high-strength metal-matrix nanocomposites.

Effect of cryogenic impact deformation and subsequent annealing on microstructure and microhardness of pure copper

This article presents an application of cryogenic impact deformation in effective grain refinement in coarse-grained copper. Ultrafine-grained microstructure was processed by means of cryogenic impact deformation using an air hammer with an initial impact velocity of 7.35ms−1. For strain ε=2.21, TEM observation showed that the initial equiaxed coarse grains (18μm) evolved into a lamellar structure of submicron size narrow domains delineated by low-angle grain boundaries. The microhardness of the deformed sample increased from 74.2±1.2HV to 118.3±1.8HV. Subsequently annealed at 190°C for 60min led to a significant reduction of dislocation density. Elongated ultrafine grains (with a mean width of 175nm) embedded with remaining nanoscale deformation twins were observed in the annealed sample. This study highlights the potential of cryogenic impact deformation to produce bulk ultrafine-grained materials.

Advanced Rolling Technologies for Producing Ultrafine-grain/nanostructured Alloys

Ultrafine-grained materials show high strength at ambient temperature, high-speed superplastic deformation at elevated temperatures, and high corrosion resistance. Such materials have attracted increasing attention in the past twenty years. A number of severe plastic deformation techniques, such as equal-channel angular press, high pressure torsion, groove pressing, twist extrusion, asymmetric rolling, and accumulative roll bonding have been used to develop ultrafine-grained bulk materials. The equal-channel angular press, high pressure torsion, twist extrusion and groove pressing techniques suffer from some drawbacks: firstly, forming machines with large load capacities and expensive dies are indispensable for these processes; secondly, the productivity is relatively very limited; thirdly, the techniques are only suitable for small samples. Compared with equal-channel angular press, high pressure torsion, twist extrusion and groove pressing, the accumulative roll bonding and asymmetric rolling techniques can be used to produce continuous ultrafine-grained sheets in large quantities. In this paper, a survey of relatively recent rolling technologies is presented. The merits and drawbacks of each technique are examined. These techniques are: (1) Asymmetric cryorolling, which has potential for large-scale industrial production of nanostructured materials; (2) Four-layer accumulative roll bonding, which has potential to produce nanostructured materials at room temperature with high bonding quality, used for fabrication of ultrafine material sheets; (3) Asymmetric Rolling of accumulative roll bonding-processed sheets, which has potential for large-scale industrial production of nanocomposite foils.

Nanoscale cracks at deformation twins stopped by grain boundaries in bulk and thin-film materials with nanocrystalline and ultrafine-grained structures

Nanoscale fracture processes initiated at intersections of deformation twins and grain boundaries (GBs) in nanocrystalline and ultrafine-grained materials are theoretically described. Within the suggested description scheme, nanocracks are formed at GBs at which deformation twins are stopped and thereby produce specific GB defect configurations that create high local stresses initiating nanocracks. The conditions for realization of this new fracture mode in nanocrystalline and ultrafine-grained materials with face-centred cubic and body-centred cubic crystal lattices are calculated. The free-surface effect on crack generation at deformation twins stopped by GBs in thin-film nanocrystalline specimens is theoretically described. The critical parameters for crack generation in nanocrystalline and ultrafine-grained bulk materials and thin films are revealed. It is shown that in bulk nanomaterials nanocracks are generated at twin thicknesses of several nanometres and grow very fast with increasing twin thickness. At the same time, in thin-film nanomaterials, the equilibrium nanocrack lengths significantly decrease if the distance between the twin lamella and the closest film surface does not exceed several twin thicknesses.

Crystallization Kinetics Analysis and SPS Consolidation of Mechanical Alloyed Fe&lt;sub&gt;79&lt;/sub&gt;Ti&lt;sub&gt;16&lt;/sub&gt;P&lt;sub&gt;5&lt;/sub&gt; Amorphous Powders

Amorphous Fe79Ti16P5 alloy powders were synthesized from commercially available elemental powders by mechanical alloying. The microstructure, thermal stability and crystallization kinetic of as-milled powders were analyzed by XRD, SEM and DSC. Moreover, bulk ultrafine-grained materials were fabricated through spark plasma sintering of the amorphous powders. Results show that the amorphous powders exists two exothermal peaks during crystallization process. The effective activation energies for crystallization are obtained 109.14 kJ/mol and 205.97 kJ/mol for Ep1 and Ep2, respectively, by using the Kissinger method. The mechanical properties of the bulk materials are remarkably improved with the increase in the sintering temperatures. The ultimate compressive strength increases from 1282 MPa to 2015 MPa, but absence of ductility.