Ceramic-matrix composites (CMCs) based on TiC–TiB2 have attracted enormous interest during recent years because, in comparison to single-phase ceramics, they exhibit superior properties including high hardness, good wear resistance and high fracture toughness. This paper begins with a review of the TiC–TiB2 equilibrium system and its possible influence on the processing and properties of the composite. The application of TiC–TiB2 composites has been limited due to the fact that they have been difficult to process. Much of the research effort has therefore focused on the synthesis, processing and fabrication of TiC–TiB2 and is based primarily on self-propagating high-temperature synthesis (SHS) and its derivatives, high-energy milling and sintering. The performance of SHS under the application of pressure has been the subject of particular investigation. These developments are the main subject of this review that also takes into account the resulting effects on the microstructure and the mechanical properties of TiC–TiB2. The influence of the reaction parameters like reactant composition, reactant particle size and green density on the microstructure and properties is also reported.

TiC-TiB2 composites : A review of phase relationships, processing and properties

A ZrB 2 -SiC composite was prepared from a mixture of zirconium, silicon, and B 4 C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa.m 1/2 . The microstructure of the composite was observed via scanning electron microscopy; the in-situ-formed ZrB 2 and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B 4 C will diffuse into the Zr and Si sites and form ZrB 2 and SiC in situ, respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.

Reactive Hot Pressing of ZrB2–SiC Composites

A ZrB2‐SiC composite was prepared from a mixture of zirconium, silicon, and B4C via reactive hot pressing. The three-point bending strength was 506 6 43 MPa, and the fracture toughness was 4.0 MPazm 1/2 . The microstructure of the composite was observed via scanning electron microscopy; the in-situ-formed ZrB2 and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B4C will diffuse into the Zr and Si sites and form ZrB2 and SiC in situ, respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.

Reactive Hot Pressing of ZrB 2 -SiC Composites

Functional coatings are widely used in energy generation equipment in industries such as renewables, oil and gas, propulsion engines, and gas turbines. Intelligent thermal spray processing is vital in many of these areas for efficient manufacturing. Advanced thermal spray coating applications include thermal management, wear, oxidation, corrosion resistance, sealing systems, vibration and sound absorbance, and component repair. This paper reviews the current status of materials, equipment, processing, and properties’ aspects for key coatings in the energy industry, especially the developments in large-scale gas turbines. In addition to the most recent industrial advances in thermal spray technologies, future technical needs are also highlighted.

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Advances in Thermal Spray Coatings for Gas Turbines and Energy Generation: A Review

Solid oxide fuel cells (SOFCs) have been under great consideration during this last decade and much effort has been dedicated to model their thermo-mechanical behavior, trying to take into account the different properties of the materials, such as their elasticity. In this paper, we report the elastic behavior of three classical materials used in SOFCs as a function of temperature: Yttria stabilized zirconia (YSZ), La0.8Sr0.2MnO3 (LSM) and Ni-YSZ. Both YSZ and LSM present unusual behaviors. The elastic modulus of YSZ first decreases slowly up to 150 °C, then dramatically up to 550 °C (certainly due to atomic motion) and finally increases probably because of an order–disorder transition (oxygen vacancies). The state of the art on zirconia was reviewed. For the LSM material, Young's modulus could not be determined below 600 °C. Above this temperature, samples with totally closed porosity present a continuously increasing modulus, while the other samples have a quite constant modulus.

Young's modulus of some SOFCs materials as a function of temperature

The ZrC-ZrB2, ZrC-TiB2, and TiC-TiB2 metal diboride-metal carbide pseudo-binary eutectic systems have been successfully solidified directionally by means of the floating zone method. The first and third of these eutectics possess a morphology consisting of columnar grains of parallel lamellae with interlamellar spacings that adhere to the lambda-squared (R) C relationship, while the second is noted to solidify in a Chinese calligraphy-like morphology of broken and deformed lamellae. This phenomenon may be related to solid solution effects, but it did not prevent the interlamellar spacings from following the aforementioned law. The calligraphic effect's values are larger than those of the other two systems, and the constant, C, is accordingly about an order of magnitude larger. All three of these cubic-hexagonal systems exhibited identical epitaxial relationships. 24 references.

H. R. Beratan

Papers

Directional solidification of (Ti, Zr) carbide-(Ti, Zr) diboride eutectics

Directional solidification of (titanium, zirconium) carbide-(ti,zr) diboride eutectics