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High Temperature Materials

High cycle fatigue study of metal–ceramic co-continuous composites

Co-continuous metal–ceramic composites synthesised by the reactive metal penetration method, starting from silica preforms and a 99.5% pure aluminium alloy, were characterised in high cycle tension–compression fatigue. The tests were performed at ambient temperature, in load control and with R = −1; the fracture surfaces were observed in a scanning electron microscope. The Wöhler curve is rather flat, suggesting that these composites behave similarly to ceramics, and the fatigue limit at 107 cycles is 91 MPa.

Alumina–zirconia–yttria nanocomposites prepared by solution combustion synthesis

Nanostructured zirconia toughened alumina composite has been prepared by solution combustion synthesis. Urea has been used as sacrificial fuel and metal nitrates as precursor reagents. A traditional composition for the final ceramic–ceramic composite has been chosen: 20 vol.% of t-zirconia partially stabilized with 3 mol% of yttria dispersed in alumina matrix.

Effect of porosity of cordierite preforms on microstructure and mechanical strength of co-continuous ceramic composites

With the aim of reducing the overall cost of the process, co-continuous metal–ceramic composites were obtained by reactive metal penetration, starting from very low cost cordierite preforms. It was investigated how the preform porosity influences both the residual porosity left in the composites after infiltration and the mechanical properties.

An analysis of carbon nanotube structure wettability before and after oxidation treatment

In this work contact angle measurements have been carried out on different carbon nanotube-based materials. Thin layers of entangled carbon nanotubes have been considered, together with thick mats of vertically aligned carbon nanotubes. Pressed single-walled carbon nanotubes and graphite have also been considered, for comparison. In particular, the properties of the as-grown thick carpets have been compared to those of the oxidized material.

Potential of SiC multilayer ceramics for high temperature applications in oxidising environment

Multilayered ceramics seem very promising for applications at very high temperatures in an oxidising environment. Actually, they present lower cost and better oxidation resistance than many conventional ceramic composites. The multilayered SiC oxidation and shock resistance has been investigated on tubular specimens processed by tape casting and pressureless sintering.

NiAl(Si)/Al2O3 co-continuous composites by double reactive metal penetration into silica preforms

NiAl(Si)/Al2O3 composites with co-continuous structure were prepared by a double reactive metal penetration technique. Silica preforms were in a first step immersed in an Al bath, obtaining an Al(Si)/Al2O3 composite, then a reactive penetration of Ni was performed, bringing to the substitution of Al with NiAl. The obtained composites present both phases continuous, and the whole process is a near-net-shape one. Various tests were performed, showing that the composites present high hardness and melting point and good modulus.

Multilayer SiC for thermal protection system of space vehicles: Manufacturing and testing under simulated re-entry conditions

Two types of laminated multilayer silicon carbide plates were processed by tape casting, de-binding and pressureless sintering. The specimens were subject to thermal re-entry testing under conditions as derived from the HERMES study: up to 100 combined thermal and air pressure cycles were performed. After the first cycle, all samples lost about 1.5% of their initial mass. This was caused by burn-off of the carbon added as sintering aid or left after thermal decomposition of binder and plasticizer used in the tape casting process.

MoSi2 laminate processed by tape casting: Microstructure and mechanical properties' investigation

In this investigation multilayered MoSi2 was processed by tape casting, stacking of layers, debinding and pressureless sintering. The debinding treatment was optimized by means of thermogravimetric analysis and the effect of the sintering temperature on both microstructure and properties of the laminate was studied.

Improving macroscopic physical and mechanical properties of thick layers of aligned multiwall carbon nanotubes by annealing treatment

In this work we present a systematic study of the effects of high temperature treatments on the macroscopic physical and mechanical properties of millimeters thick layers of self-standing vertically aligned multi wall carbon nanotubes (MWCNTs). Annealing treatments were carried out on pristine MWCNT chunks in argon gas, in the temperature range of 1500-2200 °C. The analysis showed a change in most of the physical properties as an effect of the graphitization process.

HfB2/SiC as a protective coating for 2D Cf/SiC composites: Effect of high temperature oxidation on mechanical properties

In the field of thermal shielding for aerospace applications Cf/SiC composites are raising great interest, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular HfB2, are among the best oxidation resistant materials known. A coating made of a HfB2/SiC composite (20% weight SiC) was tested as an oxidation protection on a Cf/SiC composite.