2008

Wear and failure of die casting dies involve a complex interaction between various mechanisms. The most important wear and failure modes are summarized as follows: (i) the so-called washout damages on working die surfaces are attributed to erosion, corrosion and soldering; (ii) thermal fatigue is the most important failure mode in die casting. The sector of surface thin PVD coatings is constantly enhancing in order to meet the increasing demand for improved performances of tooling. Advanced PVD coatings are designed to withstand severe mechanical and thermal stress conditions.

In this article an investigation has been carried out on different austempering cycles conducted on samples of the most diffused hot-work tool steel: AISI H 11. The laboratory tests have been addressed to the examination of the structure and to the evaluation of its mechanical properties: the hardness, the impact strength and the thermal fatigue.

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.

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 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.

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.

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.

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.

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.