Róbert Kočiško

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.

Influence of SPD by ECAP on Cu Properties

Equal channel angular pressing (ECAP) is a material processing method for developing an ultrafine-grained (UFG) structure by introducing severe plastic deformation (SPD) in a bulk material with no changes in its cross-section. Numerous analytical and numerical studies on equal channel angular pressing have been performed in recent years. The present work focuses on the effects of die geometry width is defined by the angle between two channels Φ, angle on outer corner of die Ψ (or radius R) and angle within internal corner (or radius r) of die on average effective strain after one pass route. Next, there are analyses of strength properties, plastic properties, fracture mechanism, as well as analyses of Cu structure evolution after SPD by ECAP technology, in the paper. The sixteen passes through the ECAP matrix were realized using route C. The following experimental results and their analyses, the biggest increase of strength and microhardness was proved already after 4th pass. Valuation of fracture surfaces shows that after 12th pass plastic fracture is transformed from transcrystalline ductile mixed fracture. After 4th pass, the avarage grain size decreased from initial approximate size 7 µm to 200 nm, whereby the average grain size was changeless after subsequent deformations. Possible mechanism of high-angle boundary nanograins evolution consists of formation of cell structure, subgrains that transform with the increase of deformation into nanograins with big-angle misorientation.

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.

Homogenization of AlSi7MgCu0.5 Alloy as-Cast Structure by ECAP Processing

The homogenization of AlSi7MgCu0.5 alloy as-cast structure by using an equal channel angular pressing (ECAP) was investigated. The heat treatment of as-cast alloy applied before ECAP processing was required to increase alloy plasticity. Therefore, the samples of analyzed alloy were solution annealed at temperature of 550 °C for 4 hours and subsequently water quenched. Quenched samples were artificially aged at temperature of 300 °C for 5 hours to obtain an over-aged alloy state. The solution annealing of as-cast alloy state caused a partial spheroidization and coarsening of eutectic Si-particles. During artificial aging of analyzed alloy, the incoherent particles precipitated uniformly from α-solid solution. The ECAP technique at room temperature homogenized its heterogeneous dendritic microstructure and formed the ultra-fine grains of solid solution. A redistribution and fragmentation of the eutectic Si-particles and precipitated particles was occurred.

Effect of ECAP on the Dimensional and Morphological Characteristics of High Performance Aluminium PM Alloy

The main aim of this paper is to show how ECAP influences the porosity distribution of PM aluminium alloys. The dimensional and morphological characteristics of investigated materials were measured individually for each pore. A commercial ready-to-press aluminium based powder (ECKA Alumix) was used as material to be investigated. After applying different compacting pressures (400 - 700 MPa), specimens were debinded in a ventilated furnace (Nabertherm) at 400 °C for 60 min. Sintering was carried out in a vacuum furnace at 610 °C for 30 min. The specimens were ECAPed for 1 pass. When severe plastic deformation is applied, the stress distribution in deformed specimens causes the powder particles to squeeze together to such an extent that the initially interconnected pores transform to small isolated pores, determining a given value of the dimensional characteristics. Consequently, ECAP influences the porosity distribution in terms of the involved severe shear deformation and therefore influences the pore morphology.

A COMPACTING PROCESS OF THE EN AW 6060 ALLOY

This study reports on an investigation of factors affect the process of compacting Al chips which are used to direct scrap processing through the forward extrusion method. EN AW 6060 chips of different geometry and types were mainly used as the experimental material. The chips were compacted in a die with a vertical channel (10.3mm in diameter). To provide a range of processing conditions, three different weights were selected and compacting was performed under five, different compacting pressures. The movement of the chips within the die during compacting was analysed through numerical simulations using Deform 2D software. Study of the compacting process optimal parameters for increasing the density and enhancing the density distribution were defined. The results from our study clearly show that optimal conditions are obtained when the proportion of D/h is 1/1.1. Moreover, it was recognized that in the process of small chips compacting, there was obtained lower density than in the case of large chips.

The Influence of Thermo-Plastic Processes on Materials Recovery

The influence of thermo-plastic processes through methods of severe plastic deformations (SPD) and rolling carried out at ambient and cryogenic temperatures on recovery of two materials was investigated. The aim of this study was to insert strains to materials having middle and high stacking fault energy (SFE) in ambient and cryogenic temperature conditions, respectively and subsequently, through DSC method, to observe an influence of the storage energy on structural recovery of materials. As experimental materials were used oxygen free high conductivity copper (OFHC Cu) and C-Si steel which represent materials with middle and high stacking fault energy (SFE), respectively. The OFHC Cu was subjected to equal channel angular rolling (ECAR) by seven passes. ECAR is a method belonging to a SPD group. It was shown, five ECAR passes have a significant effect on material properties. The rolling performed at cryogenic temperatures using a laboratory duo rolling mill was carried out only once. This study implies that a recovery process (characterized by the mobility of structural defects) starts as follows: for OFHC Cu without ECAR and processed by 5th ECAR passes: 0.31·Tmelt and 0.19·Tmelt, respectively, for C-Si steel processed by cryorolling: 0.095·Tmelt.

An Evaluation of Severe Plastic Deformation on the Porosity Characteristics of Powder Metallurgy Aluminium Alloys Al-Mg-Si-Cu-Fe and Al-Zn-Mg-Cu

Light weight aluminium alloys, showing excellent workability, high thermal and electrical conductivity, represent a good choice for the powder metallurgy (PM) industry to produce new materials having unique capabilities, not currently available in any other powder metal parts. Moreover the requirement on mechanical properties (i.e. high tensile strength with adequate plasticity) should assure an increasing role for aluminium alloys in the expanding PM market. Room temperature tensile strengths in aluminium based metal matrix composites (MMC) in excess of 800 MPa have been reported (Guo & Kazama, 1997). However, PM based MMC currently show very limited application, also due to the high costs of production, thus having a low commercial appeal for both producers and end users. The application for aluminium powders is basically in the production of PM parts for structural and nonstructural purposes in the transportation and commercial areas. Press and sinter products, blends of aluminium and elemental alloy powders are pressed into intricate configurations and sintered to yield net or near-net shapes. There are two interesting classes of commercial press and sinter aluminium alloys: Al-Mg-Si-Cu and Al-Zn-Mg-Cu-(Si). The first alloy displays moderate strength (the level of tensile strength is 240 MPa) while the latter alloy develops high mechanical properties (the level of tensile strength is 330 MPa) in both the assintered and heat-treated conditions. Solid solution strengthening and precipitation hardening can contribute to the higher strength values of the commercial alloys. (Pieczonka et al., 2008) report transverse strength of aluminium-based PM alloys in the range of 400 MPa (Al-Mg-Si-Cu) to 550 MPa (Al-Zn-Mg-Cu). It’s well known (Bidulska et al., 2008 a) that conventional forming methods and heat treatment can determine a limit in the level of strength-plastic characteristics adequate to structural properties. One possible way for achieving higher mechanical properties is

Numerical simulation, formation of microstructure and mechanical properties of nanocopper prepared by severe plastic deformation

The development of the nanostructure in commercial pure copper, the strength and ductility as well as fracture micromechanisms after severe plastic deformation (SPD) with the technology of equal channel angular pressing (ECAP) are analysed. Experimental results and analyses showed that both strength and ductility can be increased simultaneously by SPD. The final grain size decreased from the initial 50 μm by SPD to 100–300 nm after ten passes. An increase of the ductility together with an increase of strength caused by SPD is explained by a strong grain refinement and by a dynamic equilibrium of weakening and strengthening and it is visible on the final static tensile test stress-strain charts. The fracture micromechanism is influenced by the number of ECAP passes. Transcrystalline ductile fracture took place in the range from one to 14 passes, whereas mixed fracture (transcrystalline ductile fracture with intercrystalline facets) occurred after 15 and 16 ECAP passes. Probable reasons of different fracture mechanisms are explained. Mathematical simulations of the ECAP were realised in software product DEFORM based on the finite element method (FEM).