Structural evolution of La-Cr-O thin film: Part II. Elasto-plastic properties by nanoindentation

The goal of this research is to study the elasto-plastic properties of La-Cr-O thin films deposited by RF-magnetron sputtering on stainless steel interconnect materials after annealing at high temperatures in air. Elastic modulus, hardness and yield pressure derived from nanoindentation data are reported for thin films in different structural states. The amorphous film has an estimated elastic modulus of 174 GPa. The moduli of annealed films are calculated to be 150, 185 and 120 GPa after annealing at 500 °C, 600 °C and 800 °C, respectively. The film annealed at 800 °C has the lowest hardness and is dramatically different from the other structural states due to formation of the nanoporosity. The amorphous film and the films annealed at 500 °C and 600 °C both have hardness of 14 GPa, which is close to the value estimated by modeling.     

Effect of annealing on the microstructure, room-temperature strength, and fracture toughness of Al2O3−ZrO2−TiN ceramics

The microstructure, phase composition, room-temperature flexural strength, and fracture toughness of Al₂O₃−ZrO₂−TiN (AZT) ceramics were studied on specimens annealed in air at 1000, 1200, and 1400°C. The strength of the ceramics decreased with annealing temperature. The degradation in strength was caused by defects formed on or near the surface of the ceramics during oxidation of TiN which started at 600–700°C. The surface defects after annealing are influenced by the formation of rutile (TiO₂) at 1000 and 1200°C, aluminum titanate (Al₂TiO₅), and titanium suboxide Ti₅O₉ at 1400°C as well as by diffusion processes associated with ZrO₂. If the annealing of smooth AZT specimens in air resulted in lower strength, specimens in the form of single-edge notched beam (SENB) exhibited a considerable increase in fracture toughness (K _Ic) with annealing temperature. Such behavior was caused by the formation of an oxide layer which hindered the propagation of the main crack from the notch base. Thermal treatment of the smooth AZT specimens and further edge notching and testing did not result in a change of K _Ic values. The Al₂O₃ and Al₂O₃−ZrO₂ ceramics were also tested for comparison. Translated from Problemy Prochnosti, No. 1, pp. 132–138, January–February, 1999.     

Effects of rolling and hot pressing on mechanical properties of boron carbide-based ceramics

A study of hot pressed B₄C-based laminates, after rolling and without rolling, has been performed to elucidate the existence of fracture resistance/crack length anisotropy induced by this processing technique. While the crack lengths/fracture resistance was affected significantly by the presence of the residual stresses in B₄C/B₄C–ZrB₂ laminates, no differences in Vickers crack lengths were observed in B₄C/B₄C laminates prepared by rolling and hot pressing, as compared to the crack lengths seen in pure B₄C ceramics prepared by hot pressing without rolling. X-ray diffraction analysis confirmed that no texture has been formed during the rolling and hot pressing of B₄C ceramics.     

On thermal and vibrational properties of LaGaO3 single crystals

The thermal expansion and vibrational properties of [1 0 0] and [0 0 1] LaGaO₃ single crystals have been studied by thermal mechanical analysis and micro-Raman spectroscopy. A first-order orthorhombic to rhombohedral phase transition has been confirmed by both techniques, as well as by in situ heating using optical microscopy. The appearance of a metastable intermediate phase, tentatively assigned as monoclinic, has been detected both by optical microscopy and Raman spectroscopy upon heating of the [1 0 0] and [0 0 1] LaGaO₃ single crystals. Not only temperature, but the stress-induced orthorhombic to rhombohedral phase transition has also been detected by Raman mapping of the residual impression made by Vickers indentation. The position map of bands belonging to the lower-temperature/pressure orthorhombic and the higher-temperature/pressure rhombohedral phase show that the rhombohedral phase is located inside the impression, where the applied indentation stresses are the highest, whereas no rhombohedral phase is detected outside the impression, where the surface has not been altered by contact stresses.     

High-Temperature Oxidation of Metals with Allowance for Radiative Heat Transfer

The influence of radiation on the characteristics of high-temperature and hysteresis oxidation regimes for a metal particle with an oxide film in a condensed state on its surface is studied. Conditions are defined under which radiative heat exchange with cold walls of the reactor decreases the burning temperature, critical temperatures, and oxide-film thickness, i.e., parameters characteristic of ignition and forced and spontaneous extinction of a metal particle.     

Rheokinetics of the curing of compositions based on epoxydized urethane-containing rubbers

Viscometric characteristics of adhesive compositions of two types are investigated under different temperature-time conditions of curing: one composition is based on polyurethane rubber with terminal epoxy groups (PPG-3A) and the other, on oligodieneurethane resin (PDI-3A). Mathematical models reflecting the temperature and time dependences of viscosity are developed to optimize the bonding of highly filled polymers to rubbers. The parameters of the viscous flow of adhesive compositions based on oligodieneurethane epoxy resin are determined from the results of the experimental study. It is established that the effective activation energy of curing is 2.7-fold higher than that of the viscous flow. Technological recommendations are formulated for the application of the investigated adhesive compositions onto substrate surfaces.     

Combustion and spontaneous extinction of a carbon particle in a laser radiation field

An explanation is provided for the mechanisms of the spontaneous and forced extinctions of a carbon particle in a laser radiation field. It is shown that the particle is extinguished when the heat transfer and mass transport coefficients attain critical values. Analytical equations are derived for the diameter, at which a spontaneous transition to a quasi-steady laser burning of the carbon particle takes place. It is established that the transition to the quasi-steady high-temperature regime is possible only within a certain interval of the carbon particle dimensions. The possibility of a mechanism is shown for a process control mechanism based on changing the initial particle temperature.I. I. Mechnikov Odessa State University, 270100 Odessa. Translated from Fizika Goreniya i Vzryva, No. 1, pp. 50–56, January–February, 1995.     

Mechanical properties of 10 mol% Sc2O3-1 mol% CeO2-89 mol% ZrO2 ceramics

The mechanical properties, such as Young's modulus, Vickers hardness, indentation fracture resistance, room and high temperature four-point bending strength and SEVNB fracture toughness along with the stress-strain deformation behavior in compression, of 10 mol% Sc₂O₃-1 mol% CeO₂-ZrO₂ (ScCeZrO₂) ceramics have been studied. The chosen composition of the ScCeZrO₂ has very high ionic conductivity and, therefore, is very promising oxygen ion conducting electrolyte for the intermediate temperature solid oxide fuel cells. Therefore, its mechanical behavior is of importance and is presented in the paper.     

The effect of coating crystallization and substrate impurities on magnetron sputtered doped LaCrO3 coatings for metallic solid oxide fuel cell interconnects

For IT-SOFC metallic interconnects, surface coating is effective for reducing Cr poisoning of the cathode and controlling scale growth. In this work, LaCrO₃ and doped LaCrO₃ coatings were deposited by magnetron sputtering on SS446 and Crofer 22 APU substrates. The crystallization process was studied by means of X-ray Diffraction (XRD) during the annealing of the sputter coated samples in ambient and reducing environments. The formation of intermediate phases when annealed in air, LaCrO₄ and La₂CrO₆, results in vacancy formation upon subsequent transformation to the LaCrO₃ phase and thus a decreased oxidation resistance. While the avoidance of an intermediate phase change when the coatings are initially annealed in a reducing environment leads to dense and compact coatings. This confirmed both by XRD and by scanning electron microscopy (SEM) of coating cross-sections. Crofer 22 APU alloys with various silicon and aluminum levels are deposited with doped LaCrO₃ coating to study substrate impurity effects on coating properties. It was found that silicon content in the substrates leads to increased ASR of the coatings. In addition, long term annealing in air shows that aluminum impurities in the substrate can lead to the formation of alumina at substrate grain boundaries, which in turn leads to enhanced Mn migration at the grain boundaries. Increased manganese concentrations at the film/grain boundary interface in coated samples produces larger than normal amounts of (Mn,Cr)₃O₄ spinel in these regions, which cracks the coating and reduces the ASR value due to extra electronic conduction path. A similar mechanism is not observed in a low Al/Si alloy.