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Hot deformation and recrystallization of advanced high-manganese austenitic TWIP steels

100%

Dobrzyński L. A. , Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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tom Vol. 46, nr 1

71--78

EN

Purpose: The aim of the paper is to determine the influence of hot-rolling conditions on structure of new-developed high-manganese austenitic steels. Design/methodology/approach: Flow stresses during continuous and multi-stage compression tests were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steels were compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in different stages of hot-rolling was determined in metallographic investigations using light microscopy as well as X-ray diffraction. Findings: The steels are characterized by different microstructure in the initial state. Steel with higher Al concentration has stable microstructure of austenite with annealing twins, while steel with higher Si concentration consists of certain portion of e martensite in form of plates. The flow stresses are in the range of 200-430 MPa for the applied conditions of hot-working and are up to 40 MPa lower compared to continuous compressions. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery. On the basis of analysis of thermo-mechanical treatment carried out in continuous axisymetrical compression test and multi-stage compression test using the Gleeble 3800 simulator allowed to work out a schedule of three different variants of hot-rolling for each of investigated steels 26Mn-3Si-3Al-Nb-Ti and 27Mn-4Si-2Al-Nb-Ti. Research limitations/implications: To fully describe the hot-rolling behaviour of the new-developed steels, further investigations in wider temperature and strain rate ranges are required. Practical implications: Various conditions of hot-rolling for advanced high-manganese austenitic steels can be useful to determine influence of microstructure on mechanical properties obtained in static and dynamic tensile test. Originality/value: Microstructure evolution in various conditions of hot-rolling for advanced high-manganese austenitic steels were investigated.

2

Effect of Al additions and heat treatment on corrosion properties of Mg-Al based alloys

80%

Tański T. , Labisz K. , Dobrzyński L. A.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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tom Vol. 44, nr 1

64--72

EN

Purpose: In this paper there is presented the corrosion behavior of cast magnesium alloys in as cast state and after heat treatment. Design/methodology/approach: The following results concern scanning electron microscopy investigations in the SE as well BSE observation mode, for better phase contrast results, also qualitative microanalysis was applied for chemical composition investigations of the surface. Pitting corrosion resistance was carried out using the potentiodynamic electrochemical method (direct current), based on anodic polarisation curve. Based on the achieved anodic polarisation curves, using the Tefel extrapolation method near to the corrosion potential. the quantitative data were determined, which describe the electrochemical corrosion process of the investigated alloys: value of the corrosion potential Ecor (mV), polarisation resistance Rp (kΩ/cm2), corrosion current density icor (μA/cm2), corrosion rate Vp (mm/year) as well the mass loss Vc (g/m2). Findings: Surface morphology of the samples after corrosion test performed after and before heat treatment show irregular shaped pinholes and numerous cracks on the material surface layer. Research limitations/implications: The applied cooling rate and alloy additions seems to be a good compromise for properties and microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and parameters of solution treatment process and aging process. Practical implications: Investigation results concerning the surface layer presents some interesting findings connected to the layer morphology, which can be of high interest for practical application for the reason of better layer quality as well as surface layer properties. Limitation of surface damage including irregular shaped pinholes and numerous cracks is of very high importance for decreasing the influence of pitting corrosion onto the surface layer corrosion resistance in very width range o applications. Originality/value: The value of this paper is to define the influence of heat treatment parameters and aluminium addition on corrosion resistance properties of magnesium-aluminium cast alloys.

3

The influence of Ni-P layer deposited onto Al2O3 on structure and properties of Al-Al2O3 composite materials

80%

Dobrzyński L. A. , Kremzer M. , Konieczny J.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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tom Vol. 46, nr 2

147--153

EN

Purpose: The purpose of this work is to present the influence of wettability improvement of sintered Al2O3 particles by deposition of Ni-P coating. Design/methodology/approach: The material for investigations was manufactured by pressure infiltration method of ceramic porous preforms. The eutectic aluminium alloy EN AC - AlSi12 was use as a matrix while as reinforcement were used ceramic preforms manufactured by sintering of Al2O3 Alcoa CL 2500 powder with addition of pore forming agents as carbon fibres Sigrafil C10 M250 UNS, SGL Carbon Group Company. The Al2O3 was coated with the Ni-P alloy to improve the wettability of sintered particles. Metallographic examinations were made in the transmission electron microscope (TEM). Findings: The obtained results indicate the possibility of obtaining new materials with all advantageous properties of the particular composite constituents by infiltration of the ceramics with the liquid aluminium alloy. Practical implications: The composite materials made by the developed method can find application as the alternative material for elements fabricated from conventional materials. Originality/value: The obtained results show the possibility of manufacturing the composite materials by the pressure infiltration method of porous sintered preforms based on the ceramic particles with liquid aluminium alloy being a cheaper alternative for materials reinforced by fibres.