Barbara Grzegorczyk

Effect of Heat Input on Microstructure and Hardness Distribution of Laser Welded Si-Al TRIP-Type Steel

This study is concerned with issues related to laser welding of Si-Al type TRIP steels with Nb and Ti microadditions. The tests of laser welding of thermomechanically rolled sheet sections were carried out using keyhole welding and a solid-state laser. The tests carried out for various values of heat input were followed by macro- and microscopic metallographic investigations as well as by microhardness measurements of welded areas. A detailed microstructural analysis was carried out in the penetration area and in various areas of the heat affected zone (HAZ). Special attention was paid to the influence of cooling conditions on the stabilisation of retained austenite, the most characteristic structural component of TRIP steels. The tests made it possible to determine the maximum value of heat input preventing the excessive grain growth in HAZ and to identify the areas of the greatest hardness reaching 520 HV0.1.

Instability of Plastic Deformation in Low-Alloy Copper Alloys

The purpose of this paper is to determine the influence of temperature of plastic deformation on the structure and mechanical properties of copper alloys of the types CuCo1NiBe (CCNB), CuCo2Be (CB4), CuNi2SiCr (CNCS), CuNi1P (CNP) and CuCr1Zr (CW106C) applied on electrodesduring a tensile test. Tensile tests were carried out on polycrystalline samples of above mentioned alloys, which confirmed the presence of inhomogeneous plastic deformation in specified temperature ranges for each alloy. The tensile test of the investigated copper alloys were realized in the temperature range of 20÷800 °C with strain rate of 1.2•10-3s–1 on the universal testing machine. Metallographic observations of the structure were carried out on a light microscope and the fractographic investigation of fracture on an electron scanning microscope. Performed experimental studies have proven that analyzed structural factors, in a range of investigated strain conditions at elevated temperature, significantly influence the phenomenon of the Portevin Le Chatelier (PLC) type instability of plastic strain, revealed in low-alloy copper alloys. Moreover, it was found that the impact of examined factors on the PLC effect should be considered comprehensively, taking into account their synergic interactions.

Relation between the plastic instability and fracture of tensile tested Cu-Sn alloys investigated with the application of acoustic emission technique

The work concerns the application of the acoustic emission (AE) method in testing the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to instable plastic flow connected particularly with the Portevin-Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile test at a strain rate (?? ) of about 1.2·10-3s-1 in the range of temperatures (20÷400?C) has been analyzed. It has been found that the highest intensity of the oscillation of stresses, corresponding to the instability of plastic deformation PLC occurred at 200?C, whereas the maximum of the AE activity is at about 200÷250?C. The brittle intergranular fracture starts in the range of equicohersive temperature (TE) of about 200?C. Plastic deformation of the investigated alloy in the range of the temperature of minimum plasticity, amounting to about 400?C, results in intercrystalline fractures on the entire surface of the stretched samples.

Mechanisms of plastic instability and fracture of compressed and tensile tested Mg-Li alloys investigated using the acoustic emission method

The results of the investigation of both mechanical and acoustic emission (AE) behaviors of Mg4Li5Al alloy subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloy and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the possible influence of factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries or solute atoms along dislocations (Cottrell atmospheres) or dislocation pile-ups at grain boundaries which create very high stress concentration leading to fracture. The results show that the plastic instabilities are related to the Portevin–Le Châtelier phenomenon (PL effect) and they are correlated with the generation of AE peaks. The fractography of breaking samples was analyzed on the basis of light (optical), TEM and SEM images.

Microstructural Features of Cu-Zn Single Crystals Deformed at Elevated Temperature

Copper alloys are characterized by high plasticity and good resistance to corrosion. They are applied in electrical industry, telecommunication, in transport and machine building, particularly in the production of elements for deep drawing. The scope of investigation enclosed production of testing single crystals, determination of their crystallographic orientation, deformation of selected single crystals by compression in a temperature range from 20 °C to 400 °C, applying strain rate from 10-5 s-1 to 10-1 s-1 as well as microstructure observations. Typical plastic strain effects were observed in the microstructures of studied single crystals in the form of parallel and intersecting lines and slip bands with locally intensified density in different areas of cross section of examined specimen and the deflection bands with slightly marked slip lines in the primary system.

Influence of the Crystallographic Orientation of CuZn30 Single Crystal on the Portevin-Le Chatelier Effect

Plastic deformation of solid crystals is a complex process, mostly heterogeneous, due to the simultaneous effect of several deformation mechanisms. A dominating deformation mechanism depends on the properties of the material and external coefficients, viz. temperature, stress and strain rate. The applied Bridgman method permitted to obtain single crystal of the CuZn30 alloy adequate for plastic deformation investigations. Single crystal are characterized by selected crystallographic orientations from various areas of the basic triangle. In order to determine the influence of the crystallographic orientation on the Portevin-Le Chatelier effect selected single crystals were compressed at a temperature of 300°C at a strain rate of 10-3 s-1. Experiments confirmed the effect of the crystallographic orientation axis of CuZn30 single crystals on the observed differences in the intensity of stress oscillation on stress-strain curves.