Magdalena Bieda

Microstructure and Deposition Relations in Alumina Particle Strengthened Ni-W Matrix Composites

The nanostructured Ni-W/Al2O3 composite coatings were prepared by electrodeposition technique on ferritic steel substrates from aqueous electrolyte solutions containing ultrafine alumina particles in suspension. The effects of plating parameters like current density, inert particle concentration in plating bath and ultrasonic field frequency on the incorporation of α-Al2O3 particles (TM-DAR Taimicron) into an Ni-W matrix were investigated. The MMC coatings microstructure, phase and chemical composition were studied by means of scanning (E-SEM FEI XL-30) and transmission (TECNAI G2 SuperTWIN) electron microscopies, as well as XRD measurements (Bruker D8 Discover). SEM and TEM observations of composite cross-section microstructure showed that the presence of ultrasounds considerably reduces the particles agglomeration and enables a uniform distribution of particles in the Ni-W matrix. The electron diffraction pattern analysis revealed that the composite metallic matrix consists of an α-Ni(W) solid solution. The matrix was characterized by quasifibrous, nanocrystalline grains of an average size about 10 nm.

Investigations of Fine Grained Metallic Materials by Means of Orientation Maps in Transmission Electron Microscope

New subdivision of microscopic investigation called Orientation Microscopy (OM) is already well known in scanning electron microscope (SEM). Needs for investigation in nanoscale contribute to development of an appropriate method for transmission electron microscope (TEM). Automated acquisition and indexing of diffraction patterns, necessary for creation of orientation maps in TEM, cause more difficulties then in SEM. Nevertheless, the techniques of OM are also being developed in the Transmission Electron Microscope (TEM). Microdiffraction has been successfully introduced for creating such maps. Individual orientation measurements, which appeared in the convergent beam mode, can be used for quantitative description of microstructure of fine grained and deformed materials. The idea of the operation of the automated system in transmission electron microscope (TEM) which is developed in IMIM PAS relies on an automatic (with control position of the beam) acquisition of diffraction patterns using digital CCD camera, and indexing them, and then on the analysis of the set of individual crystallographic orientations. The graphic presentation of received sets of orientation can be analysed in order to obtain parameters and characteristics such as texture characteristics, characteristics of grain boundaries (based on orientation relationship) or the stereological characteristics. To illustrate application of this system, orientation maps measured in cold-rolled polycrystalline aluminium and its alloy 6013, and in multi-phase alloys of Fe-Cr-Co system after severe plastic deformation are presented.

Microstructure and properties of hard magnetic FeCr30Co8 alloy subjected to plastic deformation by complex loading

Abstract The microstructural, mechanical and magnetic properties of FeCr30Co8 alloy in the a state were examined after upsetting, followed by torsion. The temperatures (750, 800, 850 and 900°C) and deformation rates corresponded to the superplasticity conditions of the Fe–Cr–Co alloys. Due to the torsional deformation, which was applied only to the bottom of the samples, a gradient microstructure was formed in the sections that were parallel to the upsetting direction. In the temperature range from 750 to 850°C, the deformation led to intermetallic r-phase precipitation. The maximum refinement of the microstructure and the maximum r-phase precipitation were observed in the material that was deformed at 800°C. Measurement of the magnetic properties showed a decreasing coercive force in the deformed alloy, in contrast to the mechanical properties of the samples after the magnetic treatment.

Microstructure and some properties of FeCr25Co15 alloy subjected to plastic deformation by complex load

Abstract The microstructural, mechanical and magnetic properties of FeCr25Co15 alloy were examined after upset followed by torsion. Deformation was carried out at temperatures that corresponded to the appearance of α + γ phases. During the process, the initial lamellar microstructure of the material was transformed into a globular one. In the sample sections parallel to the upsetting direction a gradient microstructure, with a layer of submicron grains in the highest deformation zone, was formed. The thickness of the zone did not significantly depend on the deformation temperature. Measurements of the mechanical properties after magnetic treatment showed that the plasticity and strength of the deformed samples increased in comparison with the high coercive state.

Advanced characterization of microstructural changes during recrystallization in aluminum alloy 6013

Aluminum alloy 6013 was chosen as an example of a material that, after thermal treatment, possesses a relatively uniform and stable bimodal distribution of fine ( 1 μm) particles. Samples of this alloy were subjected to plastic deformation by cold rolling. The presence of large and small particles has an influence on the behavior of this material during the recrystallization process. A complex investigation of the microstructural changes during annealing were carried out by means of advanced SEM and TEM techniques. Orientation mapping (OM), i.e., automatic determination of the topography of the crystallographic orientations, was performed using electron backscatter diffraction (EBSD) in the SEM and microdiffraction in the TEM experiments. These techniques were combined with in-situ heating experiments in the TEM and SEM experiments. The quantitative description of the microstructure at each step of recrystallization is presented. Changes in the microstructure of the investigated material during annealing reveal the role and impact of both types of particles on recrystallization and grain growth. The obtained results are in agreement with parallel calorimetric studies.

Continuous and Discontinuous Recrystallization of 6013 Aluminum Alloy

In situ orientation mapping using TEM and calorimetric measurements were carried out to investigate the annealing behavior of cold-rolled 6013 aluminum alloy. The recrystallization of the material can be considered to be a number of processes that correspond to two separate stored energy release peaks. In the temperature range of the peak 1, the deformation zones around the large second-phase particles acted as sites for particle-stimulated nucleation. In the matrix, at the same time, some elongation of grains occurred. The elongated matrix grains appeared because of the reduction of the dislocation density and the annihilation of some low-angle grain boundaries between chains of subgrains lying in layers parallel to the sheet plane. The matrix processes in this temperatures range can be considered forms of continuous recrystallization. The matrix high-angle grain boundaries started to migrate at the temperature range of the peak 2. They moved mostly in the direction normal to the sheet plane. Heating of the sample for an appropriate time at those temperatures resulted in the complete discontinuous recrystallization of the material. The recrystallized microstructure was dominated now by elongated grains, which were a few times thicker than those obtained by annealing at the temperatures of the peak 1.

Microstructure and Texture Evolutions in AA1200 Aluminum Alloy Deformed by Accumulative Roll Bonding Method

The results of studies carried out on AA1200 aluminum alloy deformed by Accumulative Roll Bonding (ARB) are presented in this paper. The commercial purity material was deformed up to 10 cycles (equivalent plastic strain of 8) at room temperature. The deformed microstructures and the crystallographic textures were characterized by transmission (TEM) and scanning (SEM) electron microscopes and high resolution orientation mapping. It was found that increased deformation leads to a strong increase of quantity of high angle (>15°) grain boundaries and strong grain refinement (up to 200-300 nm). The microstructure observations and TEM and SEM local orientation measurements allowed identifying fine and strongly disoriented planar dislocation structure of nanolayers described by strong texture components close to two nearly complementary positions of {112} orientation.