Jerzy Morgiel

Microstructure of Fe–25Cr/(La, Ca)CrO3 composite interconnector in solid oxide fuel cell operating conditions

A 20 μm thick coating of La 0.8 Ca 0.2 CrO 3 perovskite on Fe-25Cr steel substrates was obtained by the screen-printing method. The interaction of the (La, Ca)CrO 3 coating with the steel substrate occurring during oxidation in air at 1073 K for 200h was investigated. The microstructure, phase and chemical analyses of the coating after oxidation were examined. It has been revealed that the metal substrate-coating interfacial zone has a two-layer structure built of mainly FeCr 2 O 4 and LaCrO 3 , which provide the electric contacts between the interconnector material and the film, thus creating conditions for prolonged exploitation of solid oxide fuel cells.

XPS study of the cBN–TiC system

Sintered cubic boron nitride is widely used in various industrial applications because of its extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with these optimal properties it is important to elucidate whether chemical reactions occur at boron nitride/bonding phase interfaces. Some of these systems were then subjected to physical and thermal alteration This paper summarizes theoretical and experimental studies on the cBN–TiC 1:1 molar ratio. From theoretical calculations it follows that TiC reacts with boron nitride forming two new phases, TiB2 and TiN. Experimentally CBN–TiC composites were prepared by hot pressing, and the samples were subsequently heat treated. The samples were characterized after heat treatment using transmission electron microscopy and X-ray diffraction.

Microstructure of Ti3SiC2-based ceramics

Abstract The Ti 3 SiC 2 -based ceramic produced by self-propagating high-temperature synthesis (SHS) has been investigated by means of analytical electron microscopy (AEM). The observations have proved that the elongated slabs with rounded corners of well fused Ti 3 SiC 2 grains form a matrix within which some rounded TiC and less frequent angular SiC inclusions are present. A TiSi 2 phase filling up a remaining free space between carbide grains, has been also detected. The Ti 3 SiC 2 grains are characterised by a high density of dislocations, while the TiC ones contain mostly stacking faults. Cracks forming in the material are situated predominantly at the Ti 3 SiC 2 TiC interface.

Microstructure and martensite transformation in aged Ti-25Ni-25Cu shape memory melt spun ribbons

The phase transformations and microstructure of Ti-25at.%Ni-25at.%Cu alloy melt-spun at 26 m/s (50 μm thick, 3 mm wide) were investigated using DSC and TEM. The as received ribbon was nearly fully amorphous with a few spherical β phase grains (of size up to 15 μm). The heating (20°C°min.) of this ribbon resulted first in restart of growth of existing large grains and later in homogenous nucleation and growth of new small β phase crystallites within the amorphous matrix. The crystallization peak temperature of amorphous parts in this ribbon was determined to be 460°C. Further heating with the same rate to higher temperatures causes precipitation predominantly at grain boundaries with maximum of its thermal effect around 600°C. Isothermal aging of crystallized ribbon cause precipitation of thin plates of a tetragonal phase. The size and density of these plate-like precipitates depends on local microstructure and differs most drastically within large primary grains. The in situ TEM experiments confirmed the presence of only B2–B19 martensite transformation in the investigated ribbon. However, in situ TEM observations showed also that this transformation was significantly retarded in areas with small grains and even more in areas of high dislocation density as compared to primary large grains. Therefore, the delay in martensitic transformation caused by differences in the microstructure was the reason for the peak splitting in DSC curves.

Effect of titanium on structure and martensic transformation in rapidly solidified Cu–Al–Ni–Mn–Ti alloys

Abstract Alloys of composition Cu–(11.8–13.5)%Al–(3.2–4)%Ni–(2–3)%Mn and 0–1%Ti (wt.%) were cast using the melt spinning method in He atmosphere. Ribbons obtained in this process showed grains from 0.5 to 30 μm depending on the type of alloy and wheel speed. Bulk alloys and most of the ribbons contained mixed 18R and 2H type martensite at room temperature (RT). Some ribbons, crystallizing at the highest cooling rate, retained also β phase due to a drop of M s below RT. The M s temperatures in ribbons were strongly lowered with increasing wheel speed controlling the solidification rate. This drop of M s shows a linear relationship with d −1/2 , where d is grain size. The strongest decrease of M s and smallest grains were found in the ribbons containing titanium due to its grain refinement effect. The cubic Ti rich precipitates, present in both Cu–Al–Ni–Ti and Cu–Al–Ni–Mn–Ti bulk, were dispersed in ribbons cast with intermediate cooling rates of up to 26 m s −1 , but suppressed for higher cooling rates. The transformation hysteresis loop was much broader in ribbons due to presence of coherent Ti rich precipitates and differences in grain size which is particularly important in the ultra small grain size range.

Electron diffraction based analysis of phase fractions and texture in nanocrystalline thin films, part III: Application examples

In this series of articles, a method is presented that performs (semi)quantitative phase analysis for nanocrystalline transmission electron microscope samples from selected area electron diffraction (SAED) patterns. Volume fractions and degree of fiber texture are determined for the nanocrystalline components. The effect of the amorphous component is minimized by empirical background interpolation. First, the two-dimensional SAED pattern is converted into a one-dimensional distribution similar to X-ray diffraction. Volume fractions of the nanocrystalline components are determined by fitting the spectral components, calculated for the previously identified phases with a priori known structures. These Markers are calculated not only for kinematic conditions, but the Blackwell correction is also applied to take into account dynamic effects for medium thicknesses. Peak shapes and experimental parameters (camera length, etc.) are refined during the fitting iterations. Parameter space is explored with the help of the Downhill-SIMPLEX. The method is implemented in a computer program that runs under the Windows operating system. Part I presented the principles, while part II elaborated current implementation. The present part III demonstrates the usage and efficiency of the computer program by numerous examples. The suggested experimental protocol should be of benefit in experiments aimed at phase analysis using electron diffraction methods.

TEM characterization of the reaction products in aluminium–fly ash couples

Abstract The reaction products region formed between molten aluminium and dense, mainly amorphous, precipitator fly ash substrate, produced by hot pressing in argon, was investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy. The observations proved the oxy-redox reactions between Al and such fly ash constituents as SiO 2 , Fe 2 O 3 , Fe 3 O 4 and mullite. It results in the formation of two interpenetrating crystalline networks, i.e., α-Al 2 O 3 particles surrounded by a continuous metallic phase (Si or Al–Si alloy, reinforced with iron aluminade precipitates). The CaO does not react with Al and its fine crystallites were observed either inside or between the α-Al 2 O 3 particles.

BN sintered with Al: Microstructure and hardness

Abstract Boron nitride (BN) was sintered with Al by high pressure hot pressing while preserving the molar ratio of BN:Al 9:1. Ready made samples were additionally annealed at 950 °C under pressure, at 3 × 10 −3 Pa for 1 h. The structure of sintered material before and after annealing was studied using transmission electron microscope. From the microscopic observations it could be concluded that the samples prepared both before and after annealing exhibit a compact structure. At the BNAl interface immediately after pressing, small crystallites of Al can be observed. Additionally, after annealing, a layer of columnar AlN grains of 0.04 μm thickness are visible. In the area between AlN and BN phases polycrystalline AlB 10 and AlB 12 phases can be seen. Hardness of the samples increases twice (~20 GPa/HK1) after annealing. Thermal treatment also results in an increase in mechanical strength of the sintered BNAl system.

Thin films of HgCdTe on silicon surfaces

Thin (about 300 nm and less) HgCdTe and CdTe films have been deposited on Si flat and anisotropically etched microrelief surfaces by YAG:Nd3+ pulsed laser at various substrate temperatures in the range from 323 K to 423 K with 100 laser shots. These films and HgCdTe/Si heterosystems were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and current–voltage characteristics (CVC) analyses. It has been shown that under above conditions laser layer deposition method forms polycrystal films of CdTe, CdHgTe both for microrelief and flat Si substrates in the low temperature range

Structural Characterization of Reaction Product Region in Al/MgO and Al/MgAl2O4 Systems

The reaction product region, formed between molten aluminium and MgO and MgAl2O4 single crystals of three different crystallographic orientations, was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectrometry (EDS). The Al/MgO and Al/MgAl2O4 couples were produced under ultra high vacuum at 800, 900 and 1000°C. The observations proved the redox reactions of Al with both MgO and MgAl2O4. Independently of crystallographic orientation of initial oxide single crystals, the reaction product region (RPR) was formed and it was built of oxide particles surrounded by continuous metallic phase. For Al/MgO couples, the RPR was composed of two layers, where in the first layer, the oxide phase was Al2O3 while in the second layer, the MgAl2O4 was identified. In the case of Al/MgAl2O4 couples, a single layer was distinguished and only the Al2O3 phase was recognized.