Papers by Keyword: Ultrafine Grained Material

Abstract: Pure copper, pure silver, Cu-6.8at%Al, Cu-1at%Mn and Cu-5at%Ni (stacking fault energies (SFEs) are about 41, 22, 23, 43 and 105mJ/m², respectively) were processed by equal channel angular pressing (ECAP) at the same homologous temperatures to investigate the effect of SFE and solute atoms on microstructural evolutions. The final grain size of Cu-6.8at%Al after eight passes of ECAP was the smallest followed by that of Cu-1at%Mn with little difference. The former alloy reaches saturation for grain size and grain boundary misorientation in early passes of ECAP while the latter continues decreasing even after eight passes. The role of shear bands and deformation twins is predominant for grain fragmentation in the early stage for Cu-6.8at%Al and Ag with low SFE while evolution from cell walls to grain boundaries is main mechanism for Cu, Cu-1at%Mn and Cu-5at%Ni with medium or high SFE. Solute Mn atom of Cu-Mn with high atomic size misfit and may suppress the dynamic recovery which transforms cell walls to grain boundaries, and allow accumulation of higher dislocations and reduction of cell size to smaller scales.

Abstract: The results of the microstructure and hardness investigations of the Cu-0.8Cr alloy after application of severe plastic deformation (SPD) implemented by rolling with the cyclic movement of rolls (RCMR) are presented in this paper. Performed substructure investigations showed that using the RCMR method can refine the microstructure of Cu-0.8Cr alloy to the ultrafine scale. The structure of the Cu-0.8Cr alloy was analyzed using light microscope (LM) and scanning transmission electron microscope (STEM). The quantitative studies of the substructure was performed with "MET-ILO" software, on the basis of images acquired on STEM microscope.

Abstract: In this work, an attempt has been made to improve the mechanical strength of 6063 aluminium alloy and thus its lightness via combination of severe plastic deformation (grain size refinement) and heat treatment (precipitation hardening). 6063 aluminium alloy was chosen as the best material for lightweight structures, where mass reduction is important, because of its high extrudability. Samples were hydrostatically extruded (HE) in supersaturated condition and subsequently subjected to an aging process. HE brings about significant grain size refinement well below 1 micron. The influence of aging parameters such as time and temperature on mechanical properties evolution of extruded material was determined. The microstructure of ultrafine grained (UFG) alloy was investigated using transmission electron microscopy. The average grain diameter and grain boundary misorientation angles (using Kikuchi lines) were measured. Mechanical properties were examined in microhardness and tensile tests. The results have shown that it is possible to combine grain boundary and precipitation strengthening and obtain ultrahigh strength in 6xxx series alloys. Additionally, heat treatment of UFG samples causes an increase in ductility measured in tensile tests, which is rather poor in severely deformed materials. To prove advantages of UFG aged samples for lightweight applications, finite element modelling was performed to compare the mass of chair elements made of coarse and ultrafine grained material. Simulations were made for the same stresses applied. It has been shown that if the chair was made of UFG aluminium alloy the mass reduction would be approximately 30 %.

Abstract: The article represents results of influence of different severe plastic deformation (SPD) techniques on TiNi alloys. It is demonstrated that strength and shape memory effect (SME) of TiNi can be significantly enhanced due to formation of ultrafine-grained (UFG) and nanocrystalline (NC) structures by SPD. Influence of equal channel angular pressing (ECAP), high pressure torsion (HPT), multi-step SPD deformations (ECAP plus cold rolling) on structure, mechanical and functional properties of TiNi alloys is considered. There are represented first results of influence of equal channel angular pressure-Conform (ECAP-C) on TiNi alloys, which is a perspective technology for industrial fabrication of UFG metals and alloys.

Abstract: Principles of fabrication of ultrafine grained bulk and sheet materials for superplastic deformation by the methods of multiple isothermal forging and warm rolling are formulated. New data on superplastic behaviour of commercial alloys, on diffusion bonding of similar and dissimilar materials, and superplastic forming of titanium alloys are presented. The recent application of the diffusion bonding and superplastic forming technology for the production of hollow blades is demonstrated.

Abstract: Steel bars having a cross section of 18mm square with uniform distribution of ultrafine ferrite grains were produced through a multi-pass warm caliber rolling process in a 0.15%C-0.3%Si-1.5%Mn steel. The average ferrite grain sizes of 0.43μ m, 0.70μ m and 1.2 μ m were obtained in the isothermal warm caliber rolling processes at 773K, 823K and 873K respectively. Even though caliber rolling results in inhomogeneous strain distribution, multi-pass caliber rolling to large cumulated strains of 2 or 3 can be uniformly introduced in to the bar samples. Strain accumulation due to the multi-pass warm deformations was confirmed by comparing microstructural evolution through the multi-pass deformations with that of single pass deformation. The size of ultrafine grains formed through warm deformation was found to depend on the Zener-Hollomon parameter. The similarity of the microstructural evolution with single pass deformation reveals that the multi-pass warm deformation is an effective method to obtain ultrafine grained ferrite structure in bulk materials. It is proposed that compressive strain-Z parameter plots along with grain size-Z parameter plots help in establishing the processing conditions for obtaining products with a desired microstructure and grain size. Finally, such “processing maps” developed for a variety of materials serve useful purpose in bridging the science and technology of developing bulk ultrafine grained materials in semi-finished / finished products.

Abstract: We present a model of severe plastic deformation of metals under the assumption of turbulence in their representative volume element. It provides simple and natural answers to a number of questions at the border between mechanics of solids and materials science.

Abstract: The quasi-static and dynamic compression experiments of ultrafine-grained copper fabricated by equal channel angular pressing method were performed at temperatures ranging from 77 to 573K. The influence of temperature on flow stress, strain hardening rate and strain rate sensitivity were investigated. The results show that the flow stress of ultrafine-grained copper shows much larger sensitivity to testing temperature than that of coarse grained copper. However, the temperature sensitivity of ultrafine-grained copper to true strain is comparative weaker than that of coarse grained copper. For the ultrafine-grained copper, both the strain hardening rate and its sensitivity to temperature of ultrafine-grained copper are lower than those of its coarse counterpart. The SRS also displays apparent dependence on temperature. The activation volume for UFG-Cu is estimated to be on the order of ~10b3 in current experiment temperature. It is suggested that the dislocation-grain boundary interactions process might be the dominant thermally activated mechanism for UFG-Cu.

Abstract: A grain size is known to be one of the factors which define mechanical properties of metallic materials. At the same time the mechanisms which regulate the deformation behavior of bulk ultrafine-grained (UFG) metals produced by the severe plastic deformation method are still a subject for intensive study and fixed ambiguously. The report presents the developed model and the results of its application for kinetic modeling of the deformation behavior of coarse-grained (CG) and UFG Ti. Modeling has been carried out considering the possible contribution of dislocation slip and ageing. Conclusions about the role of the investigated mechanisms in the appearance of the peculiarities of the deformation behavior of CG and UFG Ti have been made.

Abstract: Most ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) exibit only limited ductility which is correlated with the low strain rate sensitivity (SRS) of these materials. Recently, it was demonstrated that SPD is capable of increasing the room temperature ductility of aluminum-based alloys attaining elongations up to 150%, together with relatively high strain rate sensitivity. In the present work, additional results and discussions are presented on the effect of grain boundary sliding (GBS) and SRS on the ductility of some UFG metals and alloys. The characteristics of constitutive equations describing the steady-state deformation process are quantitatively analyzed for a better understanding of the effects of grain boundaries and strain rate sensitivity.