Lidia Lityńska-Dobrzyńska

Microstructure and Phase Constitution Near the Interface of Explosively Welded Aluminum/Copper Plates

The microstructure changes and the phase constitution within the layers close to the bonding interface strongly influence the properties of bimetallic strips. In this work, the layers near the interface of explosively welded aluminum and copper plates were investigated by means of microscopic observations, mostly with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry (EDX). The study was focused on the identification of the intermetallic phases, the possible interdiffusion between the copper and the aluminum, and the changes in the dislocation structure of the parent plates. In macro-/mesoscale, the interfaces were outlined by a characteristic sharp transition indicating that there was no mechanical mixing between the welded metals in the solid state. In micro-/nanoscale, the layers adhering to the interface show typical deformed microstructure features, i.e., structure refinement, elongated dislocation cells, slip bands, and microtwins (in copper plate). The internal microstructure of the intermetallic inclusion is composed mostly of dendrites. The electron diffractions and TEM/EDX chemical composition measurements revealed three crystalline equilibrium phases of the γ-Al4Cu9, η-AlCu, and Θ-Al2Cu type (the last one was dominant). However, most of the observed phases of the general CumAln type (also crystalline) do not appear in the equilibrium Al-Cu phase diagram. Inside the intermetallic inclusions, no significant regularity in the phase distribution with respect to the parent sheets was observed. Therefore, it was concluded that the processes occurring in the melt determined their local chemical composition.

The nitrogen-absorption isotherm for Fe-21.5 at. % Cr alloy : dependence of excess nitrogen uptake on precipitation morphology

Nitriding of Fe–21.5 at. % Cr alloy leads to a “discontinuously coarsened”, chromium-nitride/ferrite lamellar precipitation morphology in the nitrided zone. The nitrogen-absorption isotherm for this alloy with this precipitation morphology was determined at 560°C. To assure a constant precipitation morphology the Fe–21.5 at. % Cr specimen was first homogeneously pre-nitrided (at 580°C in an ammonia/hydrogen gas mixture of nitriding potential 0.103 atm−1/2) and then de-nitrided (at 470°C in hydrogen gas atmosphere). The amount of nitrogen remaining in the de-nitrided specimen indicated that the composition of the nitride precipitates is CrN and not (Fe, Cr)N. The measured nitrogen-absorption isotherm revealed the presence of excess nitrogen in the nitrided specimen, which is a surprise in view of the coarse, lamellar precipitation morphology. The occurrence of this excess nitrogen could be ascribed to an unexpected, minor fraction of the total chromium content in the alloy present as coherent, tiny nitride platelets within the ferrite lamellae of the “discontinuously coarsened” lamellar precipitation morphology, as evidenced by transmission electron microscopy. A possible kinetic background for this unusual phenomenon was discussed.

TEM Study of Quasicrystals in Al-Mn-Fe Melt-Spun Ribbon

Microstructure of rapidly solidified Al91Mn7Fe2 (at.%) alloy was investigated using SEM and TEM techniques. Quasicrystalline particles of different shapes and sizes embedded in the aluminium matrix were observed. Quasilattice constant was calculated as 0.461 Å. Additionally orientation relationships between matrix and quasicrystals particles were found based on electron diffraction patterns and high resolution images, such that: five-fold axis lie along [011] or [001] axes of the α-Al crystallographic direction.

Characterization of β and Mg41Nd5 Equilibrium Phases in Elektron 21 Magnesium Alloy after Long-Term Annealing

The paper presents results of TEM and XRD investigations of Elektron 21 magnesium alloy in as cast condition and after long-term annealing at 250 and 350°C. In as cast condition Elektron 21 consists of primary α-Mg solid solution with α-Mg-Mg3RE eutectic and regular precipitates of MgRE3. Precipitation at 250 °C causes formation of the equilibrium β phase. Annealing at 350°C caused precipitation of globular Mg41Nd5 phases on solid solution grain boundaries. Also precipitates of MgRE3 phase have been observed.

Effect of Surface Roughness and Structure Features on Tribological Properties of Electrodeposited Nanocrystalline Ni and Ni/Al2O3 Coatings

Metal matrix composite coatings obtained by electrodeposition are one of the ways of improving the surfaces of materials to enhance their durability and properties required in different applications. This paper presents an analysis of the surface topography, microstructure and properties (residual stresses, microhardness, wear resistance) of Ni/Al2O3 nanocomposite coatings electrodeposited on steel substrates from modified Watt’s-type baths containing various concentrations of Al2O3 nanoparticles and a saccharin additive. The residual stresses measured in the Ni/Al2O3 coatings decreased with an increasing amount of the co-deposited ceramics. It was established that the addition of Al2O3 powder significantly improved the coatings’ microhardness. The wear mechanism changed from adhesive-abrasive to abrasive with a rising amount of Al2O3 particles and coating microhardness. Nanocomposite coatings also exhibited a lower coefficient of friction than that of a pure Ni-electrodeposited coating. The friction was found to depend on the surface roughness, and the smoother surfaces gave lower friction coefficients.

Effect of Hot Rolling and Equal-Channel Angular Pressing on Generation of Globular Microstructure in Semi-Solid Mg-3%Zn Alloy

A combination of hot rolling and equal channel angular pressing (ECAP) was explored to generate globular microstructures in the Mg-3%Zn alloy after re-heating to the semisolid state. It was found that the single-step deformation of as-cast alloy via hot rolling at 350°C with a thickness reduction of 50% refined the alloy microstructure by creating deformation bands of the Mg (α) phase with a size of the order of tenths of micrometers. After re-heating to 630 °C, the microstructure transformed into spheroidal morphologies with an average globule size of 82 μm. An additional deformation of the hot-rolled alloy by the ECAP method at 250 °C further refined the alloy microstructure to sub-micrometer grains of lath and equiaxed shapes. After re-heating of this microstructure to 630 °C the average globule size reached 62 μm, which is roughly 25% smaller than that achieved for the hot-rolled precursor. The role of strain-induced melt activation (SIMA) techniques in generation of globular morphologies in Mg-based alloys after partial re-melting is discussed.

Physicochemical properties of hydrogel template-synthesized copper(II) oxide-modified clay influencing its catalytic activity in toluene combustion

CuO-modified montmorillonite was synthesized by the template-assisted route. Poly(acrylic acid) was intercalated into the interlayer gallery of natural clay. Subsequently, various amounts of Cu2+ cations were introduced into the prepared hydrogel–clay composite using adsorption in different volumes of aqueous Cu(NO3)2 solution at constant pH = 6. The resulting materials were finally calcined at 550 °C (chosen using the results of TGA-IR analyses) to transform them into thermally stable oxide systems. The changes in the structural properties of the clay during the progressive modification were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Moreover, porosity, reducibility and surface composition of the calcined materials were determined by means of low-temperature N2 adsorption, temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). It was shown that a high concentration of CuO nanoparticles, which were well-dispersed and protected against sintering between montmorillonite grains, and weak interaction between CuO and the clay support (resulting in easy reducibility of CuO) were the most important features influencing the catalytic activity of the synthesized materials in the total oxidation of volatile organic compounds (VOCs).

Stability and Transformation of Quasicrystalline Phase in Transition Metal Modified Al-(Mn-Fe)-based Alloys

Due to environmental and economic concerns significant interest has arisen in the development of higher strength low-density Al-based alloys for aerospace and automobile applications. One notable Alalloy strengthening approach uses fine dispersions of quasicrystalline (icosahedral) particles. These metastable phases can be formed through rapid solidification methods (e.g. melt spinning, suction casting, gas atomization), and lead to enhanced hardness (> 450 HV) and tensile strength (>1000 MPa) [1] of the obtained material. However, the high cooling rates necessary for icosahedral phase (I-phase) formation limits the final dimensions of castings to a few millimeters. Fabrication of bulk forms of quasicrystal dispersion strengthened Al alloys typically necessitates hot-compaction of melt-spun ribbon, for instance. Thus, the thermal stability of the quasicrystalline phase in these microstructures is important to retain the enhanced alloy properties after warm-extrusion or -compaction.

Structure of composites consolidated from ball milled 7475 aluminum alloy and ZrO2 powders

Abstract Nanocomposites were prepared from 7475 alloy powder ball milled for 40 h with additions of 2 % Zr and 10 or 20 wt.% of ZrO2, Y2O3 stabilized powders. Two types of ZrO2 powder additions of size near 30 nm and 0.3–0.5 μm were used. Transmission electron microscopy studies confirmed the refinement of the aluminum solid solution grain size after milling, down to about 40 nm. The milled powders were consolidated using uniaxial hot pressing in vacuum at 380 °C and at a pressure of 600 MPa. The hardness of consolidated samples was higher for the 20 % ZrO2 nanocrystalline ceramic powder addition than for 20 % ZrO2 coarser powder, at 320 and 280 HV, respectively. Transmission electron microscopy studies allowed the determination of the grain size of aluminum solid solution to be near 100 nm after hot pressing and homogeneous distribution of ZrO2 particles. The fractions of monoclinic ZrO2 were similar in the milled powder and in the hot pressed samples. ZrO2 nanoparticles did not retard the grain growth, contrary to 2 % of Zr which prevented grain growth during hot pressing. The compression tests showed 1 000 MPa of ultimate compression strength of samples with ZrO2 nanoparticles, slightly higher than those with ZrO2 larger particle additions.

SEM and TEM Characterization of NiAl2O4 Spinel Phase in Al2O3 Matrix Ni Composite

The microstructure and crystallographic relationship development of spinel phase of the composite prepared by sintering of Al2O3 and Ni powders below the melting point of Ni was investigated. Spinel phase is distributed not uniformly and the outer region of sample contains Al2O3 and NiAl2O4 without Ni particles. The differences in the microstructure between the central and surface part of the sample was clearly demonstrated. In the central part of the sample this process was only initiated and start of this reaction can be observed at the Ni/Al2O3 interface. This distribution of spinel phase is connected with the process of its formation and stability. Analysis of the crystallographic relationship between the Ni and spinel (S) indicates that the most common is the crystallographic relationship [001] S || [001] Ni or [001] S || [111] Ni. Similarly there is some statistical preference of the crystallographic relationship between spinel and Al2O3. In this case more often observed relationship is [100] S || [111] Al2O3, however similarly as in the case of Ni some deviations of several degrees are also frequent.