ULTRAFINE GRAINED ALLOYS PRODUCED BY SEVERE PLASTIC DEFORMATION: ISSUES ON MICROSTRUCTURAL CONTROL AND MECHANICAL BEHAVIOUR (original) (raw)
Related papers
Matéria (Rio de Janeiro), 2010
The present work deals with grain refinement of medium carbon steel, having different initial microstructure, modified by either thermal and/or thermomechanical treatment (TM) prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain of 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 μm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced (ε ef ~2.5 -4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. The straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The cementite lamellae spheroidization was more extensive in TM treated steel samples. The tensile behavior was characterized by strength increase for both structural steel states; however the work hardening behavior was modified in steel where preliminary TM treatment was introduced to modified coarse ferrite-pearlite structure.
Historical Studies by Polish Scientist on Ultrafine-Grained Materials by Severe Plastic Deformation
MATERIALS TRANSACTIONS
Producing ultrafine-grained (UFG) materials by means of severe plastic deformation (SPD) methods has made a significant progress within the past few decades. The topic has been of interest since the beginning of the last century at least, yet the historical studies on this subject are less-known in the SPD society. In this manuscript, the studies of the Polish scientist Stanisław Erbel including his book entitled "Mechanism of Change of Properties of Metals Subjected to Large Deformations" written in 1976 are reviewed. Although American physicist Percy W. Bridgman published a book earlier on the principles of SPD in 1952, Erbel's book is probably the first book dedicated to the formation of UFG materials by SPD processing. In this book, Erbel presented details of a high-pressure torsion (HPT) device for obtaining large strains, mechanism of microstructural fragmentation during large straining, evolution of mechanical properties (hardness, tensile properties and torque), and characterization of the microstructure by means of transmission electron microscopy (TEM). The TEM studies included not only ex-situ observations but also in-situ observations to examine the dislocation motion and thermal stability.
Ultrafine-Grained Stainless Steels after Severe Plastic Deformation
Metals
The aim of the present review is to summarize the recent achievements in the development of ultrafine-grained austenitic/ferritic stainless steels processed by large strain deformation. Various aspects of microstructure evolution and its effect on the properties of processed steels are considered. The paper starts from an overview of various methods of large strain deformation that are successfully used for producing ultrafine-grained metallic materials. Then, the structural mechanisms responsible for grain refinement during plastic deformation are considered and discussed from the viewpoint of their efficiency and effect on the subsequent recrystallization behavior. Finally, some physical and mechanical properties of ultrafine-grained stainless steels are observed. It is concluded that the development of ultrafine-grained microstructures during severe plastic deformation results from a kind of continuous dynamic recrystallization. Namely, the misorientations among the strain-induce...
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005
The dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests, using a torsional Kolsky bar, were conducted on four steel specimens, two of which were annealed at 480 °C after ECAP, and then the test data were compared in terms of microstructures, tensile properties, and adiabatic shear-band formation. The equal-channel angular pressed specimen consisted of very fine, equiaxed grains of 0.2 to 0.3 µm in size, which were slightly coarsened after annealing. The dynamic torsional test results indicated that maximum shear stress decreased with increasing annealing time, whereas fracture shear strain increased. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen. Their width was smaller in the equal-channel angular pressed specimen than in the 1-hour-annealed specimen, but they were not found in the 24-hour-annealed specimen. Ultrafine, equiaxed grains of 0.05 to 0.2 µm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries. These phenomena were explained by dynamic recrystallization due to a highly localized plastic strain and temperature rise during dynamic deformation.
Ultrafine Grained Steels by Advanced Thermomechanical Processes and severe Plastic Deformations
La Metallurgia Italiana
On the wake of the advances in Australia and Japan in achieving even finer grain sizes, the European steel companies became particularly interested in the prospects for 1 mm-UFF. For this reason, under the auspices of the European Community for Steel and Coal (ECSC), a preliminary one-year feasibility study was commissioned in 1999 to assess the properties and prospects for bulk manufacture of fine (sub-micron/micron) structures and starting from the results of this project, another project was commissioned. During this new research, different refining mechanisms and innovative deformation cycles applied to a wide range of chemical compositions were studied. The primary objective of the project was to optimise processing routes for 2-3 µm grained mixed microstructures in the bulk or surface layers of strip, plate or rods. The metallurgical aspects were focused on processing routes that do not require extreme strains and significant plant changes, through the study of microalloying a...
Production of Bulk Ultrafine Grained Steel through Severe Plastic Deformation
In the present research, a combined forward extrusion-equal channel angular pressing (FE-ECAP) was developed and used for production of bulk ultrafine grained steel in the high temperature conditions. In this method, two different deformation steps including forward extrusion and equal channel angular pressing takes place successively in a single die. The deformation process was performed at different deformation start temperatures (800, 930, and 1100 °C). In addition, 3D finite element simulation was used to predict the hot/warm deformation parameters such as strain and temperature variations within the samples during deformation. The results show that the EF-ECAP process is effective in refining the grains from initial size of 32 µm to final size of 0.9 µm after executing of extrusion and ECAP on as received samples. The main mechanisms of grain refinement were considered to be strain assisted transformation, dynamic strain-induced transformation, and continuous dynamic recrystallization.
Crystals
In the present study, the microstructure, mechanical properties, and stored energy of an aluminum alloy containing iron-rich fine precipitates, subjected to severe plastic deformation through equal-channel angular pressing (ECAP), were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Up to four passes through ECAP resulted in significant nanometer-scale grain refinement, as well as the accumulation of lattice defects, such as dislocations and mesoscopic shear planes. This resulted in a noticeable enhancement in the Vickers microhardness and the flow stress after ECAP. Differential scanning calorimetry results showed that the ECAP’ed material exhibited two exothermal peaks at 222 ± 2 °C and 362 ± 2 °C, with total thermal effects of ΔH = 4.35 and 6.5 J/g, respectively. Slight increases in the ECAP’ed material microhardness and flow stress were observed at 200 °C. The heat release, at a relatively low tem...
Tribological properties of ultrafine-grained materials processed by severe plastic deformation
Journal of Materials Science, 2012
Processing by severe plastic deformation (SPD) has been developed extensively over the last two decades in order to produce ultrafine-grained (UFG) materials having submicrometre or nanometre grain sizes. An important material property for UFG materials is good wear resistance so that they may be used in a range of structural applications. An examination of the published data shows that only limited reports are available to date on the wear behaviour of SPD-processed materials and, furthermore, many of these results appear to be conflicting. The correlation of hardness and wear is limited because the wear property is a system property that in practice is influenced by a range of factors. Accordingly, this review is designed to examine recent reports related to the wear resistance of materials processed by SPD with particular emphasis on alloys processed using equal-channel angular pressing (ECAP), high-pressure torsion (HPT) and accumulative roll-bonding (ARB).
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005
In the present study, ultrafine-grained microstructures of a conventional 5083 aluminum alloy were fabricated by equal-channel angular pressing, and their dynamic deformation and fracture behavior were investigated. Dynamic torsional tests were conducted on four aluminum alloy specimens using a torsional Kolsky bar, and then the test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear-banding behavior. The equal-channel angular-pressed (ECAP) specimens consisted of ultrafine grains and contained a considerable amount of second-phase particles, which were refined and distributed homogeneously in the matrix as the equal-channel angular pressing pass number increased. The dynamic torsional test results indicated that the maximum shear stress increased, while the fracture shear strain remained constant, with increasing equal-channel angular pressing pass number. Observation of the deformed area beneath the dynamically fractured surface showed that a number of voids initiated mainly at second-phase particle/matrix interfaces and that the number of voids increased with increasing pass number. Adiabatic shear bands of 200 to µm in width were formed in the as-extruded and 1-pass ECAP specimens having coarser particles, whereas they were hardly formed in the four-pass and eight-pass ECAP specimens having finer particles. The possibility of adiabatic shear-band formation was explained by concepts of absorbed deformation energy and void initiation.