Grzegorz Boczkal

Formation and Properties of Amorphous/Crystalline Ductile Composites in Ni-Ag-P Immiscible Alloys

The aim of the work was to investigate the influence of silver as a modifying constituent on structure formation in Ni-P based glass forming matrix. Nickel-phosphorus-based Ni80P20, Ni78Ag2P20 and Ni76Ag4P20 alloys were prepared from 99.95 wt % Ni, 99.95 wt % Ag, and Ni-P master alloy. The alloys were melt-spun in helium. The microstructure of the melt-spun ribbons was investigated by XRD, a light microscope and a transmission electron microscope. Then the tensile tests were performed. The alloys with silver show lower tensile strength with respect to the fully amorphous Ni80P20 ribbon. The ductility of the amorphous matrix melt-spun Ni78Ag2P20 and Ni76Ag4P20 alloys was improved by addition of silver forming fcc-Ag precipitates in comparison with Ni80P20amorphous alloy. SEM observations of the fracture surfaces show different character of the fractured samples. The pattern and the number of the crack lines changes, depending on the silver content. For the fully amorphous Ni80P20 alloy simple brittle cracks are observed, however the alloys with silver content show more developed surfaces near the fractured regions and form crack lines arranged 60° with loading direction.

Oscillatory Structure of the Zn-Cu-Ti Single Crystals

Structures obtained during Zn-Cu-Ti single crystal growth by the Bridgman method were investigated. The alloys of composition Zn-Cu0.1wt.%-Ti0.1wt.% were used for single crystals growth, which were produced at rate in the range of 1.8mm/h to 16mm/h. The Zn-Cu-Ti alloys were characterized by multiphase structure; in the solute-hardened matrix by Cu atoms exists a needle-shaped intermetallic phase Zn16Ti. The strong anisotropy of the hexagonal structure gives a significant influence on a second phase distribution in the matrix volume. In the range of the low growth rates (from 1.8mm/h to 10mm/h) oscillatory structures were observed. That effect vanished at the growth rates higher than 10mm/h. The observed oscillatory structures were characterized by existing periodic layers rich in the intermetallic phase of Zn16Ti interlaid with pure matrix (alpha phase Zn with Cu solute).

The Influence of Growth Rate on Mechanical and Thermodynamical Properties of the Zn-Ti0.075-Cu0.15 Single Crystals Deformed at (0001) System

The single crystals were produced from industry zinc alloy containing 0.075wt.% of titanium and 0.15wt.% of copper. The Bridgman method was applied to obtain the single crystal. Three growth rates were used: 6mm/h, 10mm/h and 16mm/h. The common feature of all of the produced single crystals was homogeneous distribution of the second phase on a sections normal to the growth direction. The investigated single crystals were deformed in compression test with jump changes of the strain rate (from 10-4s-1 on 10-3s-1). From the obtained stress-strain curves the Critical Resolved Shear Stress (CRSS), hardening coefficient in the easy slip range (QA) and thermodynamical – activation volume (V*) and activation enthalpy (DH) were determined. The tests were done at the temperature range from 77K to 400K. Results showed anomaly on the CRSS=f(T) curve. The temperature of an extreme was 240K. The same effect was observed on V*=f(T) and DH=f(T) curves. The presented results reveal good correlation with crack phenomena that was observed during a bent of the zinc alloy sheets at the temperatures below 300K.

Control of the Single Crystal Reinforcement by the Intermetallic Compound Layers

. An improvement of the Brody & Flemings theory has been proposed to study not only the solute segregation but the solute redistribution during the single crystal growth as well. The redistribution is treated as a phenomenon superposed upon the segregation phenomenon. The crystal growth has been performed by the closed Bridgman system with a constant growth rate and an imposed temperature gradient. A hypo-eutectic Zn-Ti alloy has been subjected to oriented growth and precipitation of the Zn-16Ti intermetallic compound was observed. The precipitates have been placed as some layers distributed within the single crystal with a constant spacing. Some data from the Zn-Ti binary phase diagram was introduced into the theory to show possibility of the control the phenomenon of the reinforcement by precipitation during a single crystal growth.

Studies on the mechanical properties of steel–TiB2 composites obtained by high pressure sintering

ABSTRACT The currently used composites produced by classical sintering methods are characterised by numerous limitations due to the difficulties in combining different materials with extreme properties. One of the ways to overcome these limitations is in the use of modern sintering methods, including the high pressure-high temperature process. This study describes the composite materials based on 316L austenitic steel reinforced with titanium diboride and examines the effect of sintering conditions on the mechanical properties and microstructure of sintered composites. It has been found that the key parameter in the manufacture of composites with optimal properties is the sintering time and temperature, while martensitic transformation taking place in the composite matrix can be controlled by the properly selected pressure applied during the sintering process.

Numerical Models of Vacancy Diffusion Based on Crystal Structure

The paper discusses influence of main structural factors, as the type of crystal structure and net constant, on macroscopic features of self-diffusion and interdiffusion, in an attempt to provide a consistent description of diffusion that would involve all relevant physical effects, such as Kirkendall effect, dependence of diffusion on vacancy concentration, crystallography, and concentration of individual elements.Basing on the model structure, which is a Simple Regular net along with a corresponding Wigner-Seitz cell, the principal assumptions of the proposed model are presented as well as its implications, in order to determine general relations, which can further be used in numerical calculations involving diffusion streams. Subsequently, example calculations are performed for a simplified case of a two-dimensional Simple Regular net.The conclusions reached through this line of reasoning are then extrapolated to more complicated cases of diffusion – FCC, BCC, and HCP nets – which makes possible to relate particular material structures with diffusion rates. The connection of Wigner-Seitz cells with diffusion constitutes a good demonstration of dependence of the diffusion stream on the crystallographic orientation as well on the corresponding diffusion anisotropy for complex networks.