Editorial

Structural materials for use in high-temperature oxidising environments are currently limited mostly to silicon carbide, silicon nitride, oxide ceramics and composites of these ceramics. Unfortunately, however, the maximum use temperature of silicon-based ceramics is limited to ∼1600°C due to the onset of active oxidation (lower in water vapour environments), while oxides have exhibited high creep rates at elevated temperatures. The development of structural materials for use in oxidising and rapid heating environments at temperatures well above 1600°C is therefore of great engineering importance.

Ultra-High Temperature Ceramics, UHTCs, are a family of compounds that display a unique set of properties, including extremely high melting temperatures (>3000°C), high hardness, and good chemical stability and strength at high temperatures. They are typically considered to be the carbides, nitrides and borides of the transition metals, but it is the Group IV compounds (Ti, Zr, Hf) plus TaC that are generally considered to be the main focus of research due to their superior melting temperatures and the stability of their high-melting temperature oxides that form in situ. This combination of properties makes these materials potential candidates for a wide variety of high-temperature structural applications, including engines, hypersonic vehicles, plasma arc electrodes, advanced nuclear fuels, fusion first walls and divertors, cutting tools, furnace elements and high-temperature shielding.

The 11 papers collected in this special issue of Advances in Applied Ceramics represent a selection of topics, all of which were discussed at the Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications IV conference. The meeting took place in Windsor, England from 17th September to 20th September 2017, and was the fourth conference in the series, which began a decade earlier in 2008. All four conferences were organised under the auspices of Engineering Conferences International (ECI), a not-for-profit global engineering conferences programme, originally established in 1962, that provides opportunities for the exploration of problems and issues of concern to engineers and scientists from many disciplines. The purpose of the Windsor conference was to bring together disparate researchers from academia, government and industry in a single forum that allowed the researchers to interact with designers and engineers to discuss state-of-the-art research and development efforts, what the results mean in a broader context and how to move the technology forward toward near-term and longer-term use.

The papers cover a range of topics based on monolithic ceramics and their composites made from transition metal carbides, nitrides and borides. Issues covered include opportunities and challenges arising for their use in hypersonic space vehicles, a range of different manufacturing processes used to make these materials, how they are tested and their response to oxidation, computational investigations into their microstructures, stability, phase transformation and high temperature behaviour, ultra-high temperature ceramic matrix composites and applications in advanced nuclear fuel.

We sincerely hope that this issue of Advances in Applied Ceramics will be useful to researchers working in the field of ultra-high temperature ceramics, their composites and MAX phases.

Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications IV (UHTC -IV) is sponsored and supported by ECI