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K. Miernik and S. Pytel

Abstract

The paper presents results of microstructure and mechanical properties of the dual phase (DP) steel plate with 12 mm thickness produced by intercritical annealing at a two-phase region of ferrite and austenite (α + γ) and direct quenching in water. In addition the tempering treatment at temperature of 650°C was applied to investigate effect of martensite softening on mechanical properties of the tested steel. The parameters of heat treatment were designed to achieve the high strength while retaining optimum impact strength of the DP steel.

Open access

K. Stan, L. Litynska-Dobrzynska, A. Góral and A. Wierzbicka-Miernik

Microstructure of conventionally cast and melt spun Al91Mn7Fe2 alloy was examined by X-ray diffraction, SEM and TEM techniques. Three different phases were found in a mould cast ingot: Al6(Mn, Fe), Al4(Mn, Fe) and aluminium solid solution. Rapidly quenched ribbons cast using melt spinning technique with different speed values of rotating wheel: 25, 30 and 36 m/s had average width in a range of 30-50 μm. It was found that ribbons contain quasicrystalline particles with different sizes and shapes including large dendrites in a range of micrometers and smaller spherical particles below 1 μm embedded in an aluminium matrix. Composition of these particles was similar to the Al4(Mn, Fe) phase. Also quasicrystals in the form of eutectic were observed with slightly different composition close to the Al6(Mn, Fe) phase. All observed particles revealed 2, 3 and 5- fold symmetry, typical for icosahedral quasicrystals. Increase in microhardness up to 274 HV for melt spun ribbon comparing to 141 HV for the as-cast ingot was observed due to a change in phase composition and refinement of the phases. Thermal stability of quasicrystalline phase in the ribbon was examined by annealing in different temperatures. Temperatures for thermal treatment were chosen based on DSC curve which contains the exothermic peak in the temperature range 300-500°C. Analysis of ribbons annealed for 30 minutes at 400°C showed that transformation of quasicrystals to stable crystalline phase starts at quasicrystal/Al-matrix interfaces. After annealing for 4 hours at 500°C only the Al6(Mn, Fe) phase and aluminium solid solution were observed in the ribbon microstructure.

Open access

M. Hebda, H. Dębecka, K. Miernik and J. Kazior

Abstract

The influence of adding different amounts of silicon carbide on the properties (density, transverse rupture strength, microhardness and corrosion resistance) and microstructure of low alloy steel was investigated. Samples were prepared by mechanical alloying (MA) process and sintered by spark plasma sintering (SPS) technique. After the SPS process, half of each of obtained samples was heat-treated in a vacuum furnace. The results show that the high-density materials have been achieved. Homogeneous and fine microstructure was obtained. The heat treatment that followed the SPS process resulted in an increase in the mechanical and plastic properties of samples with the addition 1wt. % of silicon carbide. The investigated compositions containing 1 wt.% of SiC had better corrosion resistance than samples with 3 wt.% of silicon carbide addition. Moreover, corrosion resistance of the samples with 1 wt.% of SiC can further be improved by applying heat treatment.

Open access

K. Stan, L. Litynska-Dobrzynska, P. Ochin, A. Wierzbicka-Miernik, A. Góral and J. Wojewoda-Budka

Influence of Ti, V, Cr, Zr, and Mo additions on microstructure and mechanical properties of the Al91Mn7Fe2 quasicrystalline alloy produced by the melt spinning technique has been studied. It was found that the microstructure of obtained all ribbons was similar and consists of spherical or dendritic icosahedral quasicrystalline particles embedded in an aluminium matrix coexisting with small fraction of intermetallic phase. Comporing DSC curves obtained for each sample it was observed that the alloy with Mo addition exhibits the best thermal stability among prepared alloys. Addition of molybdenum caused a significant shift of the main exothermic peak corresponding to temperature of quasicrystalline phase decomposition from 450ºC for ternary alloy to about 550ºC for quaternary composition. Microhardness measured for all prepared alloys were similar with the mean value of about 200 HV only alloy with Zr addition exhibited higher microhardness of about 270 HV caused by strengthening effect of Zr localized in the grains of aluminium matrix.