J. Bidulska

A study of the hot formability of an Al-Cu-Mg-Zr alloy

The high-temperature plasticity of a Zr-stabilised 2014 aluminium alloy was investigated in a wide range of temperatures and strain rates. The microstructure of representative torsioned samples was analysed by transmission electron microscopy, and the characteristics of particle and precipitate distribution were quantitatively estimated. The strain-rate dependence on stress and temperature was analysed by means of the conventional constitutive equations used for describing hot-working behaviour as well as a modified form of the sinh equation, where the stress was substituted by an effective stress, i.e., by the difference between the stress and a threshold stress. This temperature-dependent threshold stress was found to be a fraction of the Orowan stress generated by precipitates increasing from 62 to 94% as temperature decreased from 773 to 573 K.

Effect of High-temperature Sintering and Severe Plastic Deformation on the Porosity Distribution

The paper focused on the effect of high-temperature sintering along with the back pressure equal channel angular pressing (ECAP-BP) on the porosity distribution in powder metallurgy (PM) aluminium alloys. Analyses of the dimensional and morphological parameters indicate that high-temperature sintering couples to ECAP-BP lead to porosity reduction and improve pore morphology. ECAP-BP influences the porosity distribution in terms of the severe shear deformation involved and therefore influenced the pore morphology along with pore distribution.

Effect of various processing conditions on the tensile properties and structural developments of EN AW 2014 aluminium alloy

The paper deals with the influence of processing conditions on tensile properties, hardness and structure development of the aluminium alloy EN AW 2014, depending on various processing conditions (as-rolling, quenching, severe plastic deformation SPD by equal channel angular pressing ECAP and ageing). The evaluated tensile properties showed that ECAP has the highest effect on the material properties of aluminium alloy EN AW 2014. Severe plastic deformation by means of ECAP caused rapid increase of strength and only partial decrease of ductility was achieved. Strengthening of material is caused by grains refinement and strain hardening of solid solution. Based on the results above, the tensile properties, hardness and structure development of the EN AW 2014 alloy are discussed.

Nanostructure Formation and Properties in Some Al Alloys after SPD and Heat Treatment

Influence of SPD process realized by ECAP on structural formation and mechanical properties was searched. Samples after ECAP were heat treated at various temperature and time conditions. Investigation material bases were high purity aluminium and aluminium alloys EN AW 6082, EN AW 2014. The best material properties are describing in dependence on experimental conditions.

The Production of Cracks Evolution in Continuously Cast Steel Slab

Abstract The prediction of evaluation a U- and V-shaped cracks on the surface and subsurface of a continuously cast steel slab, is investigated during hot rolling. The numerical simulation is carried out by means of FE-code DEFORM 3D. Therefore, an algorithmic decision tree was developed by the C 4.5 program and applied in prediction of surface and subsurface defects behaviour during the numerical simulation of hot rolling. Cracks were selected as a transversal and longitudinal to the rolling direction. In addition to the transversal and vertical U- and V-shaped cracks on the surface; subsurface defect, referred as “circle hole”, on the side part of workpiece were evaluated. In terms of surface defects evolution, U-shaped cracks show a deteriorating influence during hot rolling. On the basis of the algorithmic decision tree established, the prediction of cracks evolution (defined before plastic deformation process) during hot rolling is examined.

Wear Mechanism of Chromium Pre-alloyed Sintered Steel

The paper is focused on the wear mechanism of a chromium pre-alloyed Fe (Cr Mo) C sintered steel. The wear behaviour of the sintered steel is investigated through pin-on-disk tests. Two different processing conditions have been used, involving a slow cooling rate of 0.05 K/s and a process called sinter hardening with an average cooling rate of 6 K/s from the sintering temperatures (1453 and 1513 K). The microscopic investigations reveal deformed layers and tracks along the direction of sliding during wear. Particular attention has also been paid to the friction coefficient and to the role of porosity on wear.

From Micro to Nano Scale Structure by Plastic Deformations

Nowadays, the strategy for improving of mechanical properties in metals is not oriented to alloying followed by heat treatment. An effective way how to improve the mechanical properties of metals is focused on the research looking for some additional structural abilities of steels. Structural refinement is one of the ways. Refinement of the austenitic grain size (AGS) carried out through plastic deformation in a spontaneous recrystallization region of austenite, formation of AGS by plastic deformations in a non-recrystallized region of austenite will be considered as potential ways for AGS refinement. After classic methods of plastic deformations, next structure refinement can be obtained by an application of severe plastic deformation (SPD) methods.

MECHANICAL PROPERTIES AND POROSITY OF Ti-6Al-4V ALLOY PREPARED BY AM TECHNOLOGY

PATRIK PETROUSEK1, JANA BIDULSKA1, ROBERT BIDULSKY1, ROBERT KOCISKO1, ALICA FEDORIKOVA1, RADOVAN HUDAK 2, VIKTORIA RAJTUKOVA 2, JOZEF ZIVCAK 2 1Technical University of Kosice, Faculty of Metallurgy, Institute of Materials, Kosice, Slovak Republic 2Technical University of Kosice, Faculty of Mechanical Engineering, Department of Instrumental and Biomedical Engineering, Kosice, Slovak Republic DOI: 10.17973/MMSJ.2017_02_2016190

MECHANICAL PROPERTIES OF POWDER CoCrW-ALLOY PREPARED BY AM TECHNOLOGY

This study is focused on the evaluation of mechanical properties and microstructure of fabricating Ni-free CoCrWalloy. Samples were prepared by additive manufacturing technology – selective laser melting. The chemical composition of used metal powder was – 60.5% Co, 28% Cr and 9%W. Parameters of SLM were given by powder supplier. The shape of thesampleis designed according to MPIF. After recommended heat treatment, the static tensile test was carried out at Tinius Olsen machine, the microstructure and porositywere observed, also. In results is interpreted the relations between porosity, microstructure, and mechanical properties. This report is the basis for further experiments aimed at improving the mechanical properties about manufacturing conditions.

Response of the Cr-alloyed PM Steels on Vacuum Sintering and Heat Treatment

Abstract The present paper deals with the evaluation of different vacuum heat treatments on the fracture surfaces of a low alloyed sintered steel in correlation with the mechanical and plastic properties achieved. The heat treatment conditions consist of the sintering process in vacuum furnace at 1393 K for 1800 s with an integrated final tempering at 473 K for 3600 s. The average cooling rates were calculated in the range of 1393 K to 673 K and were 0.1 K/s, 0.235 K/s, 3 K/s and 6 K/s, respectively. Vacuum heat treatment performed is supporting bainite/martensitic microstructure with increasing cooling rates; it provides a marked increase in strength coupled to a decrease in ductility. The typical microstructure appearances on the fracture surfaces show that microstructure-fracture developments are closely associated with strength/plastic properties. The fracture surface mode at higher magnification revealing two main micromechanisms of fracture: brittle (transgranular cleavage fracture) and ductile (dimples and plastic deformation by slip). Finally, the cooling rate of the vacuum furnace in order of 3 K/s is sufficient to obtain suitable properties of strength and plasticity which can however be accepted for several applications.