Alexander P. Zhilyaev

Bulk Nanostructured Materials: Fundamentals and Applications

Now, we come to offer you the right catalogues of book to open. bulk nanostructured materials fundamentals and applications is one of the literary work in this world in suitable to be reading material. Thats not only this book gives reference, but also it will show you the amazing benefits of reading a book. Developing your countless minds is needed; moreover you are kind of people with great curiosity. So, the book is very appropriate for you.

Recent developments in modelling of microhardness saturation during SPD processing of metals and alloys

Ultrafine-grained and even nanostructured materials can be fabricated using severe plastic deformation to ultra-high strains in equal-channel angular pressing (ECAP), high-pressure torsion (HPT), machining and their combinations, such as machining of ECAP specimens, HPT of ECAP billets and HPT of machining chips. This report presents recent results of investigations of the microstructures and microtextures of pure copper, nickel and aluminium subjected to different deformation processes to ultimately high imposed strains. A comparison of the microstructure, dislocation density and microhardness developed during combinations of different strain paths is performed. All characteristics were analysed by X-ray, transmission and scanning electron microscopy, and electron backscatter diffraction (EBSD). The influence of different processing routes is discussed in terms of the accumulated strain and microstructure refinement. The saturation in grain refinement is examined with reference to the recovery taking place during ultra-high strain deformation. A phenomenological model based on the Voce equation is applied for fitting parameters based on the experimental data and this is suggested for a prediction of microhardness evolution for pure metals (Ag, Au) and Cu-based (Zn, Al) alloys.

Adiabatic heating and the saturation of grain refinement during SPD of metals and alloys: experimental assessment and computer modeling

Severe plastic deformation methods include equal-channel angular pressing/extrusion, high-pressure torsion, and plane strain machining. These methods are extremely effective in producing bulk microstructure refinement and are generally initiated at a low homologous temperature. The resulting deformation-induced microstructures exhibit progressively refined cellular dislocation structures during the initial stages of straining that give way to refined, equiaxed grain structures at larger strains. Often, grain refinement appears to saturate but frequently coarsening is observed at the largest strains after a minimum in grain size is attained during SPD. Here, we summarize results on grain refinement by these processing methods and provide an analysis that incorporates adiabatic heating to explain the progressive refinement to intermediate strains and that may be followed either by an apparent saturation in grain refinement or by grain coarsening at the largest strains. This analysis is consistent with continuous dynamic recrystallization in the absence of the formation and long-range migration of high-angle boundaries.

Reassessment of temperature increase and equivalent strain calculation during high-pressure torsion

The problems of temperature increase during high-pressure straining and equivalent strain calculation are reassessed on the basis of general considerations and experimental evidence. Temperature evolution is measured for some pure fcc and hcp metals (Cu, Al, Ni, Ti and Zr) and different regimes of HPT (pressure, strain accumulated and strain rate). The results obtained are compared with modelling and theoretical estimates. A simple model taking into account microstructure evolution during HPT is applied in order to explain the consequent straining-hardening-softening. The heat release of plastic work is calculated on the basis of both the von Mises and Hencky equivalent strains giving some assessment on the applicability of these equations.

Microstructure and microtexture evolution in pure metals after ultra-high straining

Ultrafine-grained, and even nanostructured materials can be manufactured by ultra-high straining by equal-channel angular pressing (ECAP), high-pressure torsion (HPT), by machining, and through combinations, such as machining of ECAP specimens, HPT plus ECAP, and HPT of machining chips. This report describes the results of investigations of the microstructure and microtexture of pure aluminium and copper subjected to different deformation processes to high imposed strains. The microstructures, dislocation densities, and microhardness developed during combinations of different strain paths were investigated and all characteristics were analyzed by X-ray, transmission and scanning electron microscopy, and by orientation imaging microscopy. The influence of different processing routes is examined in terms of the accumulated strain and microstructure refinement. A saturation in grain refinement is also considered with reference to the occurrence of recovery during ultra-high strain deformation.

Effect of high pressure torsion on the microstructure evolution of a gamma Ti–45Al–2Nb–2Mn–0.8 vol% TiB2 alloy

The technique of high pressure torsion (HPT) has been widely used to refine the microstructure of many metallic materials, especially pure metals and disordered alloys. Comparatively fewer studies have, however, been carried out in intermetallics. γ-TiAl alloys are envisioned as high potential materials to replace Ni superalloys in some turbine components due to their good performance at high temperatures and light weight. Exploring the potential beneficial effects of severe plastic deformation techniques in these materials is now timely. In this work, a γ-TiAl alloy with a lamellar microstructure has been processed by HPT using pressures ranging from 1 to 6 GPa and 0 to 5 anvil turns at room temperature. Significant refinement of the microstructure via twin formation, bending of the lamella and the accumulation of a high dislocation density upon the application of shear give rise to a drastic hardness increase.

Microstructure changes in ultrafine-grained nickel processed by high pressure torsion under ultrasonic treatment

HIGHLIGHTSEffect of ultrasound on the microstructure of severely deformed nickel is studied.Ultrasound exerts a relaxing effect on the structure of nanostructured materials.Effect of ultrasound on the structure of nanomaterials depends on its amplitude. ABSTRACT Commercially pure nickel was processed by high pressure torsion (HPT) and subjected to ultrasonic treatment (UST) with different amplitudes of compression‐tension stresses in the zone of stress antinode of a standing wave. It was found that microstructure parameters such as the dislocation density, low‐ and high‐angle grain boundary fractions, microhardness, and the stored excess energy as well, non‐monotonically depend on the ultrasound amplitude. A structure relaxation leading to a reduction of internal stresses and stored energy and increase of the fraction of high‐angle boundaries was observed at some intermediate amplitudes of the oscillating stress. The maximum relaxation effect was observed in the samples after UST with the amplitude of 60 MPa. Possible mechanisms of the influence of ultrasound on the microstructure of deformed materials are discussed.

Factors influencing the development of homogeneity in disks processed by high-pressure torsion

High-pressure torsion (HPT) is an important processing technique in which a disk is subjected to a high pressure with concurrent torsional straining. In principle at least, the imposed strain is zero at the center of the disk and a maximum at the outer edge. This difference suggests, therefore, that materials processed by HPT will exhibit considerable inhomogeneity. This paper describes the results obtained in a series of experiments which were designed to evaluate the evolution of homogeneity during the processing of two materials by HPT. It is demonstrated that it is possible to achieve a reasonable level of homogeneity in both materials but there are important differences which reflect the dependence of the microstructure on the occurrence of dynamic recovery.

Microhardness and EBSD microstructure mapping in partially-pressed al and cu through 90º ECAP die

Equal-channel angular pressing (ECAP) is widely recognized as an effective method for processing ultrafine-grained and even nanostructured materials. Important details on processes occurring in the die intersections can be obtained by mapping the microhardness and EBSD microstructures in partially-pressed aluminum and copper through the 90o die of ECAP. Precise measurements were made using grids of partially-pressed Al and Cu and detailed color maps were plotted and compared with EBSD maps. A narrow region along the bisector of two channels reflects altering in microhardness level of the material subjected to simple shear. The microstructural evolution suggests significant refining of the grain structure but there is noticeable inhomogeneity in the microhardness and microstructure for both materials. Factors contributing to the inhomogeneous hardness distribution include the coarse initial grain size, and inhomogeneous deformation across the plane of the die channel intersection due to die wall friction and the formation of a dead zone at the outer corner.

Novel Method of Severe Plastic Deformation - Continuous Closed Die Forging: CP Aluminum Case Study

There is a large number of methods for severe plastic deformation (SPD). Multidirectional forging (MDF) is probably one of the most easily scalable for industrial application. In general, two main conditions need to be fulfilled for successful SPD processing: constant sample geometry and application of a quasi-hydrostatic pressure. The first condition is necessary for strain accumulation by repetitive deformation and the second one helps preventing cracking in the specimens with high accumulated strain. However, MDF is not providing quasi-hydrostatic condition in the processed sample. This paper reports a novel method for severe plastic deformation, namely continuous closed die forging (CCDF), which fulfils both requirements for the successful deformation of samples to a very high accumulated strain. Commercially pure aluminum (1050) was processed to a total strain of 24 by CCDF. After processing, the microstructure was refined down to a mean grain size of 0.78 μm. Tensile testing showed good mechanical properties: yield strength and ultimate tensile strength of the ultrafine-grained aluminum were 180 and 226 MPa, respectively. Elongation to rupture was about 18%. The microstructure, microhardness and grain boundary statistics are discussed with regard to the high mechanical properties of the UFG aluminum processed by this novel method.