Papers by Author: Rinat K. Islamgaliev

Abstract: Recent studies have demonstrated that ultrafinе-grainеd (UFG) alloys processed by equal channel angular pressing (ECAP) and high pressure torsion (HPT) can exhibit enhanced supеrplacticity at relatively low temperature and/or high strain rates. At the same time severe plastic deformation (SPD) of aluminium alloys is often carried out at elevated temperatures leading to various grain size and volume fraction of precipitates. The significance of the SPD temperature for commercial 1420 and 1421 aluminium alloys has been evaluated in this paper using in-situ heating of thin foils in the column of a transmission electron microscope. Superplastic characteristics of alloys processed at various ECAP temperatures are discussed.

Abstract: Microstructure and mechanical properties of pure nickel processed by high pressure torsion (HPT) and equal channel angular pressing (ECAP) have been investigated in the present paper. The uniformity of microstructure and misorientation angles in the SPD samples were studied using transmission electron microscopy and electron back scattering diffraction. Microstructural requirements for achivement of high strength and ductility in SPD metals are discussed.

Abstract: In the present work we studied microstructure of ultra fine grained (UFG) pure Mg and UFG Mg-based alloys. The initial coarse grained samples were deformed by high pressure torsion (HPT) using pressure of 6 GPa. Such deformation leads to formation of UFG structure in the samples. The severe plastic deformation results in creation of high number of lattice defects. Therefore, we used positron annihilation spectroscopy (PAS) for defect characterizations. PAS represents a well developed non-destructive technique with high sensitivity to open volume defects like vacancies, vacancy clusters, dislocations etc. In the present work we combined PAS with TEM and XRD to obtain complete information about microstructure of the UFG samples studied. We have found that microstructure of HPT-deformed Mg contains two kinds of regions: (a) ”deformed” regions with UFG structure (grain size 100-200 nm) and high number of randomly distributed dislocations, and (b) ”recrystallized” regions with low dislocation density and grain size of few microns. It indicates some kind of dynamic recovery of microstructure already during HPT processing. On the other hand, homogenous UFG structure with grain size around 100 nm and high density of homogeneously distributed dislocations was formed in HPT-deformed Mg-9.33 wt.%Gd alloy. After characterization of the as-deformed microstructure the samples were subsequently isochronally annealed and the development of microstructure with increasing temperature and recovery of defects were investigated.

Abstract: Bulk samples of pure Mg and Mg-Gd alloys were prepared by high-pressure torsion (HPT). The HPT made samples exhibit ultra fine grained (UFG) structure with grain size around 100 nm. Results of microstructure investigations of the UFG samples obtained by positron lifetime (PL) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) are presented. In particular, lattice defects introduced by HPT were characterized. The data obtained at atomistic level are compared with macroscopic properties given by microhardness measurements.

Abstract: In the present work, positron annihilation spectroscopy (PAS) is employed for microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP). Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the microstructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.

Abstract: Two methods were used for the analysis of submicro-crystalline copper prepared by high-pressure (6 GPa) severe plastic deformation. Conventional powder XRD study was carried in terms of the modified Williamson-Hall (WH) plots and shown large line-broadening anisotropy. A new high-resolution small-angle transmission diffuse scattering method was applied for determination of crystallite size. Two methods were used for the evaluation of the diffuse scattering - calculation of the autocorrelation function of the crystalline shape by the transformation of the measured signal and by the direct fitting. Bimodal block size distribution has to be assumed for annealed samples. This was also confirmed by classical back-reflection film method as well as by the long tails of conventional diffraction profiles.