Ivan Saxl

Anisotropy of internal stresses in poled PZT ceramics

Abstract A simple theoretical model is proposed to describe the anisotropic distribution of internal stresses in poled PZT ceramics. The anisotropic distribution of grain-boundary microcracks observed in poled coarse-grained PZT type ceramics is explained and characterized using the quantitative methods of stereology. Finally, the observed anisotropy of bending strength is discussed.

Influence of the number of passes under equal-channel angular pressing on the elastic-plastic properties, durability, and defect structure of the Al + 0.2 wt % Sc alloy

The regularities of the influence of the number of passes under equal-channel angular pressing on the mechanical properties and defect structure of an aluminum alloy have been elucidated. It has been established that the degradation of the mechanical properties (a decrease in the durability) is associated with the formation of nanoregions of an excess free volume in the course of severe plastic deformation under equalchannel angular pressing. A correlation between the nucleation of excess free volume regions and the formation of high-angle grain boundaries under equal-channel angular pressing has been revealed. The nature of the influence of severe plastic deformation on the elastic modulus, the vibration decrement, and the microplastic flow stress has been analyzed.

Nanoporosity of Fine-Crystalline Aluminum and an Aluminum-Based Alloy

The presence of nanopores formed during the equal-channel angular pressing of aluminum is revealed using small-angle x-ray scattering. The parameters of nanopores are determined, and a correlation between the level of nanoporosity and the fraction of high-angle grain boundaries is found. The data obtained indicate that the level of nanoporosity can affect the tensile durability of fine-crystalline aluminum in the creep mode. The data on the regularities in the development of nanopores under deformation of the fine-crystalline aluminum-based alloy in the superplasticity mode are obtained.

Effect of Equal-Channel Angular Pressing (ECAP) on creep in aluminium alloys

This paper examines the effect of equal-channel angular pressing (ECAP) on creep behaviour of pure aluminium, binary Al-0.2wt.%Sc alloy and ternary Al-3wt.%Mg-0.2wt.%Sc alloy. The ECAP was conducted at room temperature with a die that had a 90° angle between the channels and 8 repetitive ECAP passes followed route BC. Constant stress compression creep tests were performed at 473 K and stresses ranging between 16 to 80 MPa on ECAP materials and, for comparison purposes, on the initial coarse-grained materials. The results showed that the creep resistance of the ECAP processed Al-Sc and Al-Mg-Sc alloys was markedly deteriorated with respect to unpressed coarse-grained materials.

Inhomogeneity of microstructure and creep of ECAP Aluminium

High purity (99.99%) pure aluminium processed by equal channel angular pressing (ECAP) was examined in terms of the ECAP microstructure inhomogeneity and its creep behaviour. The results indicate that an inhomogeneity of the ECAP microstructure in mesoscopic scale may influence the creep behaviour of the pressed material.

Non-homogeneous distribution of internal stresses and cracks in poled PZT ceramics

Abstract The spatial distribution of intergranular cracks in poled coarse-grained PZT ceramics is found to be non-homogeneous with a higher density of cracks in the central region of the specimen and a lower density near the electrodes. As the cracks are formed by internal stresses (due to motion of 90° walls) it is also concluded that the distribution of internal stresses (even in fine-grained transducers without any cracks) is non-homogeneous on a macroscopic scale with the highest peak stress values in the central region.

Grain size estimation: w–s diagram

Voronoi tessellations generated by various point processes including translation and displaced translation lattices are examined as models of grain structures. The computer-simulated cell systems are sectioned by random planes and lines, and the assumptions used in the standard grain size classifications are tested.

Structural Non-Homogeneity and Thermal Instability of ECAP Aluminium

The grain structure of pure aluminium processed by equal channel angular pressing (ECAP) was examined electron backscattered diffraction (EBSD) in the as pressed state and after heating preceding the creep deformation using various stereological methods. Area intensities of grain and subgrain boundaries, length intensities of triple grain and subgrain junctions, structural homogeneity and its thermal stability are strictly dependent on the number of passes.

Analysis of spatial arrangement of particles in thin foil of Al-Al4C3 material

TEM images of thin foils with quasi-globular particles are examined by means of two methods of spatial statistics. The spatial arrangement of particle reference points is described by means of quadrat count statistics and by polygonal method (the analysis of the Voronoi mosaic generated by patterns of particle reference points). A good agreement between the both approaches is found, the polygonal method is more sensitive and its results are more conclusive.

Significance of Microdefects Induced by ECAP in Aluminium, Al-0.2%Sc Alloy and Copper

This paper deals with an experimental investigation of the effect of various microdefects induced by equal-channel angular pressing (ECAP) on mechanical and creep properties of ultrafinegrained pure aluminium, an Al-0.2%Sc alloy and copper.