A.R. de Arellano López

Microstructure–mechanical properties correlation in siliconized silicon carbide ceramics

The microstructure and high temperature mechanical properties of siliconized silicon carbide ceramics (reaction bonded, reaction formed, and biomorphic SiC) have been investigated. The microstructural differences between these materials have been analyzed. Reaction formed and biomorphic SiC show better, high temperature compressive creep resistance and strength than reaction bonded SiC. Additionally, these two materials show a continuous decrease in the creep rate, which is more pronounced at higher temperature and silicon content. This behavior is explained in detail by using a model of creep controlled by a viscous intergranular phase. The maximum strengths were exhibited by the biomorphic SiC when compressed in the axial direction. The strength of reaction formed SiC is roughly the average between the strength of biomorphic SiC compressed in the axial and radial directions. The dependence of the high temperature compressive strength with the microstructure, and volume fraction of SiC is discussed in terms of the minimum solid area approach.

Correlation between magnetic and mechanical properties of devitrified glass-coated Fe71.8Cu1Nb3.1Si15B9.1 microwires

Abstract The effects of the thermal treatment on the coercivity and mechanical behaviour of glass covered Fe71.8Cu1Nb3.1Si15B9.1 microwires have been investigated. Variations of the coercivity, Hc, with the annealing are attributed mainly to the devitrification process in this kind of microwires. The annealing temperature dependencies (300–700°C) of Hc exhibit some peculiar differences with respect to that of the classical Finemet ribbon, especially in the temperature range of 400–500°C (very beginning of the nucleation of the nanocrystallization process) and at 650–700°C (magnetic hardening owing to the iron borides segregation). Correlation of coercivity with the tensile strength after annealing has been observed. Character of the fracture studied by the scanning microscopy changes significantly with annealing.

Thermal conductivity and phase evolution of plasma-sprayed multilayer coatings

Multilayer coatings were prepared using small-particle plasma spray to investigate the effect of interfaces on thermal conductivity and phase stability. Monolithic and multilayer alumina and yttria partially-stabilized zirconia coatings, with 0, 3, 20, and 40 interfaces in 200–380 μm thick coatings were studied. Thermal conductivity was determined for the temperature range 25 °C to 1200 °C using the laser flash method and differential scanning calorimetry. Thermal conductivity of the multilayer coatings was accurately modeled by a series heat transfer equation, indicating that interfacial resistance plays a negligible role in heat transfer in the direction perpendicular to the coating plane. Powder X-ray diffraction results indicate that identical phase transitions occur in all the coatings. Independent of coating microstructure (i.e. layer thickness), as-sprayed γ-Al2O3 transforms to α-Al2O3 after 100 hours at 1200°C; as-sprayed metastable t′–ZrO2 converts to a mixture of t–ZrO2 and c–ZrO2 after 100 hours at 1300 °C. Thus, the results indicate that the interfaces do not aid in stabilizing the as-sprayed phases after prolonged severe heat treatments.