A. L. Vasiliev

Improved interfacial mechanical properties of Al2O3-13wt%TiO2 plasma-sprayed coatings derived from nanocrystalline powders

Abstract The interfacial toughness of two types of Al 2 O 3 -13wt%TiO 2 plasma-sprayed ceramic coatings on steel substrates—“conventional” and “nano”—has been measured using the Rockwell indentation method. The interfacial toughness of the “conventional” coating and the “nano” coating is found to be 22 and 45 J.m −2 , respectively. The “conventional” coating, which was prepared using a fused feedstock powder available commercially, has a microstructure consisting primarily of fully-molten (FM) and solidified “splats”. The feedstock powder for the “nano” coating comprised reconstituted agglomerates of nanocrystalline Al 2 O 3 and TiO 2 powders. The microstructure of the “nano” coating, as characterized using scanning and transmission electron microscopy techniques, consists of regions of FM “splats” interspersed with partially-molten (PM) rounded microstructural features. The substructure in these PM features (20–50 μm diameter) consists of α -Al 2 O 3 grains (0.5–1 μm) surrounded by a TiO 2 -rich amorphous phase. The FM/steel interfaces in both the “conventional” and the “nano” coatings are found to be cracked (before mechanical testing), whereas the PM/steel interfaces in the “nano” coating are found to be adherent. It is believed that the unique bimodal microstructure, together with the presence of the TiO 2 -rich amorphous phase at the PM/steel interface, is responsible for the significantly improved interfacial toughness of the “nano” coating. The key differences in the failure modes in the two types coatings are also discussed, with reference to a simple model.

STRONG DEGRADATION OF PHYSICAL PROPERTIES AND FORMATION OF A DEAD LAYER IN FERROELECTRIC FILMS DUE TO INTERFACIAL DISLOCATIONS

ASTRACT Dislocations are the most common type of secondary defects and are unavoidaly present in all crystalline materials. They have een oserved in ferroelectric materials as in many other materials systems. Experiments have shown that they may have a significant impact on the degradation of the electrical properties and may change phase transition characteristics in epitaxial ferroelectric thin films. In this study, we provide a general overview of experimental oservations comined with a preliminary thermodynamic analysis.

Crystallization of Glassy Powder from Aluminum-Rare Earth- Transition Metal Alloys

The microstructures exhibited by gas atomized powders of two alloys, Al-6Gd-6Ni-1Fe and Al-5Y-10Ni (at. %), have been analyzed using electron microscopy. It was found that the microstructure depends critically on the particle size obtained during atomization. Small particles ( 30μm) are often fully crystalline, consisting of fine interspersed Al and intermetallic grains.

Microstructure And Ternary Phases In Al-rich Al-Y-Ni Alloys.

The results of a transmission electron microscopy study on the crystal structures and morphologies exhibited by each of the phases in a set of four Al-rich Al-Y-Ni alloys which contain 1.7–4.5 at. % Y and 3.5–10.1 at. % Ni are presented. It is shown that each alloy contains fcc-Al, a binary Al 3 Ni or Al 3 Y phase (depending on alloy composition), and a ternary phase. The same ternary phase was found in each alloy and this was found to correspond to a new phase Al 19 Ni 5 Y 3 (Cmcm, a=0.4025 nm, b=0.799 nm and c= 2.689 nm, Al 19 Ni 5 Gd 3 structure type). In many cases, the ternary particles also contain embedded slabs of the equilibrium Al 23 Ni 6 Y 4 phase. This phase mixture did not decompose even after extended annealing.

Phase Formation in Ti (Ta)-Ni and Co-Ti Films Deposited on (001)Si in N 2 Atmospheres.

A series of electron microscopy investigations on the microstructure produced by surface-diffusion reactions between Si substrates heated to 700–800°C and Ti-Co, Ti-Ni or Ta-Ni alloys deposited in a nitrogen ambient with and without barrier layers are described. The TEM data show clear phase separation into TaSi 2 and NiSi 2 for the Ta-Ni film deposited in a high N 2 pressure ambient. Deposition at lower N 2 pressure led to the formation of a mixed Ni-Ta-Si layer. The phase separation effect was also absent for Ni-Ti films even at high N 2 pressure. The presence of barrier layers strongly affected the surface diffusion reactions in the Co-Ti-Si system. Formation of Ti-(O) or CoSi x amorphous layers at the Si surface prevented the interdiffusion of Si and Co, such that even pure Co or Co 2 Si layers could be formed.

Crystallographic Description for Nanoparticle Asemblies - Application to Cadmium Selenide Clusters

Abstract : The stacking sequence of several layers of self-assembled semi-conducting CdSe nanoparticles has been investigated using transmissien electron microscopy. FCC HCP saddle sites occupation and ring structures were found coexisting in the supercrystals formed by CdSe nanoparticles.