Péter Barkóczy

Simulation of Recrystallization by Cellular Automaton Method

Nowadays the quick development of computer technology has made it possible to simulate the transformation processes in the materials in a com plex way, by approximating more and more the physical reality. The recrystallization is one of the most frequently simulated transformation process. Of the simulation methods the classical C ellu ar Automation and the Monte Carlo method [1] has been used by most of the research workers. Our a im has been to develop such an automation which is based on known physical principles and is suitable for the calculation and display of grain structure in the monophase material between hot rolling. The simulation The two-dimensional automation is able to handle a cell space building 512x512 cells. The cells are squares which create a lattice on the plane. The Neuman neighbourhood is defined as the surroundings of one cell. The state of one cell is determined by its crystallographic orientation and by its energy. The rule of state-change is the same in cas e of each part-process: if in a given step the energy of cell is higher than the activation energy of a give n part-process, then the process proceeds and the cell state changes. Three part processes proceed i n the simulated grain structure: the nucleation, the grain growth and the grain coarsening. The simulation does not contai n the recovery. The cell can have a thermal energy, a grain boundary energy and a st ored energy coming from the deformation depending on the fact wether it can be found inside the g rain or on the grain boundary, or if it is deformed or recrystallized. The stored energy does not depend on the place and it does not depend on the crystallographic orientation of the grain either, it is de termined only by the extent of deformation. The value of stored energy can easily be measured by using a DSC e quipment [4]. The modules of simulation The simulation consists of modules operating according to the aforement ioned principles. These modules are the following: plastic deformation, recrystallizati on (nucleation, grain growth) and grain coarsening [5]. The plastic deformation As the first step of simulation a plastic-deformed grain struct u e is developed by the simulation using geometric principles [7,8] according to the following procedure: Th local vectors ( v) giving the plastic-deformed grain structure are obtained such a way t hat the local vectors describing the original structure ( u) is multiplied by the deformation matrix ( E). v = Eu (1) Materials Science Forum Online: 2003-01-15 ISSN: 1662-9752, Vols. 414-415, pp 359-364 doi:10.4028/www.scientific.net/MSF.414-415.359

The Effect of Melt Flow on the Dendrite Morphology

The anisotropy of dendritic structure is characterized in this paper. The direction of move of liquid/solid interface influence the velocity of the melt flow. In the course of the experiments the liquid/solid interface was moved in three different directions: i) at right angles to the direction of gravity vector, ii) in the direction identical with it and iii) in the direction opposite to it. Our purpose was to investigate the shape of solidifying dendrites as a function of the angle included by the gravity vector and solidification [6]. The measurements were done in real images fixed by us. The following parameters were chosen for characterizeing the anisotropy of dendrites: intersection number of the test lines and dendrite interface (P), orientation factor (), dendritic surface in volume (SV). The material was solidified by using an equipment developed by the authors. The solidification rate is a constant value: 0.001 mm/s and 0.003 mm/s, the composition of material used for modelling purposes is: SCN (succinonitrile) -2.5-3 mass% of acetone. 100 images were processed in each direction. It was necessary to rotate the images in order to count the number of intersections. A program developed by the authors was used for this purpose; the number of intersections was given by the program as a function of the angle of rotation, and the perimeter and area of the dendrites.

Investigation of the Kinetic of a Bainitic Reaction upon Heating in a CuAlNiMn and a CuAlNiMnFe Shape Memory Alloy

The examination of solid state processes leading to the degradation of the shape memory behaviour is essential with respect to the suitability of shape memory alloys. Besides degradation processes occurring during relatively long periods of time called ageing, bainitic reactions that suddenly degrade the shape memory behaviour were also observed in many Cu-based shape memory alloys. The mechanisms and effects of the bainitic reactions on the shape memory characteristics were investigated in many Cu-based systems, but the kinetic of the reaction was not examined so far. In the present paper, an examination was carried out on a CuAlNiMn and a CuAlNiMnFe shape memory alloy to reveal what kinetic model describes the bainitic reaction occurring and thus completely destroying the shape memory effect during one stage of heating.

Examination of the Microstructure of the Findings from Cannon Foundry Sárospatak

The Rákóczi Museum of the Hungarian National Museum revealed a cannon casting foundry in the territory of the castle of Sárospatak. The excavation started in the summer of 2006. A great amount of findings were revealed from the metallurgical, alloying and casting processes of the foundry. The Archeometallurgical Research Group of the University of Miskolc examines the microstructure and the chemical composition of these findings. The aim of this research work is to complete the knowledge of the contemporary literature and reconstruct the technological processes of the foundry. In this article the current status of the examination is introduced.

Complex metallographic study on Gepid bronze and silver buckles from the Great Hungarian Plain (5-6th cent.)

ABSTRACT This work presents a complex metallographic examination of bronze, silver and golden artefacts from early medieval German (Gepid) cemeteries of the Hungarian Plain, focusing on the finds from Tiszapüspöki.A newly developed non-destructive X-ray diffraction method was applied on the artefacts for the first time, as a novel approach, for sampling-free residual stress measurements. Other techniques such as optical microscopy and scanning electron microscopy combined with energy dispersive spectrometry has also been used. In addition to residual stress, crystallographic texture and properties of the reflections were analysed as well. The combined application of these methods was found to be an effective tool to deduce the production technologies of the examined artefacts. In addition to defining the characteristics of the material structures and compositions on the surfaces of the artefacts, the typical traces of several technological methods as casting, forming, coating were detected which are used for making various types of artefacts.

Tradecraft of the Avars’ metalworking – manufacturing of iron axes and a special multi-metallic method used for belt accessories

ABSTRACT Metallographic analyses were performed on several types of early medieval iron axes (hammers) and on a piece of a belt set, found in Hungary, using optical and SEM-EDS microscopes. The examinations were focusing on defining structural constituents, determining their distribution and grain size. Inclusions were also investigated. On the basis of the result traces and characteristics of different technological methods of forging could have been detected. The examined axes were supposedly forged from a piece of inhomogeneous iron without folding, kept at high temperature for a longer period and forged the edges multiple times, not intensely. The belt accessories were covered by an iron oxide layer, however, the complex investigation revealed that these belt ornaments are made of various metals. Sandwich-type iron-tin plates, thin iron wires as well as brass and bronze plates have been used in the product. We were able to reconstruct the steps of the production process.

Arrowheads and chainmail fragments from the Crusader Al-Marqab Citadel (Syria): First archeometallurgical approach

ABSTRACT Selected iron arrowheads and samples of iron and copper-based chainmail fragments from the medieval citadel of Al-Marqab (Qal’at al-Marqab, Margat, Syria) were examined by the Archaeometallurgical Research Group of the University of Miskolc (ARGUM) using various methods. The examination includes X-ray screening, optical microscopy (OM), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) and microhardness tests, in order to determine the composition, microstructure and mechanical properties of the finds and the manufacturing processes (e.g., traces of forming and probable heat treatment) used by Crusader and/or Mamluk metalworkers. Although the highly saline and humid atmosphere of the coastal environment of the fortress was detrimental to the iron and even to the copper-based objects, the complex examination has been very useful to acquire an in-depth knowledge of the material characteristics of the finds. The results indicate different kinds of manufacturing processes were employed on the arrowheads made of wrought iron, and a typical technique for making the links of the chain. In terms of application, two kinds of arrowheads were unearthed. The widened leaf-shaped ones, which might have been made for the use of crossbows, are fully corroded and often cracked lengthwise. In addition, two types can be found among these wide leaf-shaped arrows, those that are slightly smaller and those that are bigger. During the manufacture of thinner spiked-shaped armor-piercing arrowheads, sufficiently hard raw materials (such as pieces of bloom containing a relatively high amount of carbon or recycled iron) or wrought iron were available for the smiths. In the case of wrought iron, obtained from bloomery process, the hardness of the material could be improved by different methods (forge-hardening or cementation), which mostly depended on the master’s professional knowledge and preference.

Identification of Eutectic Microstructure by HPP Cellular Automata in Aluminum Alloys

The eutectic structure of aluminum alloys has different morphology. To describe these a different image processing and analysis workflow needs to be built. To assign the different image processing steps to the different structure automatically a computational method had to be developed. In the image processing methods several cellular automata operate. For this expediently a cellular automaton was developed to classify the different eutectic structures. In materials engineering applications a HPP automata is used extensively therefore this type of automata were chosen to solve the mentioned problem. This article shows the simplicity of this method as well as the desired evaluation method.

The Effect of Strain Path Change Form Wire Drawing to Uniaxial Compression in Al0.25Mg Alloy

In this paper the effect of the strain path change was studied in aluminum alloy containing 0,25% Mg. In metals alloys different metal forming processes can create strong crystallographic and morphologic texture. Both of them can cause direction dependency of the mechanical and other properties. The aim of this paper is to analyze how the effect of the increasing reduction of cold drawn wire appears as a result of the uniaxial compression performed in the direction opposite of drawing. Compression test were performed. Through the results of these tests the changes of the direction of deformations were analyzed qualitatively and numerically. These results provide the possibility to use uniaxial compression test to evaluate the mechanical behavior of cold drawn aluminum.

Microstructure and Texture Evolution in Cladded Al 3003 Aluminum Sheets

In the present research, the texture variation during cold rolling of cladded 3003 type aluminium sheets was examined by means of X-ray diffraction. The aluminum sheets were formed in a series of 14 rolling steps, after which texture examinations were performed on both cladded and base material sides of the sheets. After certain rolling steps, the texture was also examined by removing layers from the sheets by electropolishing to reveal the texture distribution along depth. The texture was characterised through the calculation of volume fractions of the main rolled texture components. Local drawbacks were found in the texture versus thickness reduction function. The texture was found to be higher in the middle of the sheets than at the surface.