Composites are, in general, a rapidly evolving and growing technical field with a very wide range of applications across the aerospace, defence, energy, medical and transport sectors as a result of their superior mechanical and physical properties. Ultra-high temperature ceramic matrix composites, UHTCMCs, are a new subfield within the wider grouping of CMCs that offer applications in rocket and hypersonic vehicle components, particularly nozzles, leading edges and engine components. The design and development of structural materials for use in oxidising and rapid heating environments at temperatures above 1600°C is therefore of both great scientific and engineering importance. UHTC materials are typically considered to be the carbides, nitrides, and borides of the transition metals, but the Group IV compounds (Zr, Hf & Ti) plus TaC are generally considered to be the main focus of research due to the superior melting temperatures and stable high-melting temperature oxide that forms in situ . This review presents the selection, processing, properties, applications, outlook and future directions of UHTCMCs.

This paper reports the electrochemical, optical and thermal effects occurring during flash sintering of 8 mol % yttria-stabilized zirconia (8YSZ). In-situ observations of polycrystalline and single crystal specimens revealed electrochemical blackening/darkening during an incubation period prior to flash sintering. The phenomenon is induced by cathodic partial reduction under DC fields. When using a low frequency AC field (0.1–10 Hz) the blackening is reversible, following the imposed polarity switching. Thermal imaging combined with sample colour changes and electrical conductivity mapping give a complete picture of the multi-physical phenomena occurring during each stage of the flash sintering event. The partial reduction at the cathode causes a modification of the electrical properties in the sample and the blackened regions, which are close to the cathode, are more conductive than the remainder of the sample. The asymmetrical nature of the electrochemical reactions follows the field polarity and causes an asymmetry in the temperature between the anode and cathode, with the positive electrode tending to overheat. It is also observed that the phenomena are influenced by the quality of the electrical contacts and by the atmosphere used.

This paper was published in the journal Applied Materials Today and the definitive published version is available at http://dx.doi.org/10.1016/j.apmt.2016.11.004.This research paper investigates the suitability of ceramic multicomponent materials, which are found on the Martian and Lunar surfaces, for 3D printing (aka Additive Manufacturing) of solid structures. 3D printing is a promising solution as part of the cutting edge field of future in‐situ space manufacturing applications.\ud 3D printing of physical assets from simulated Martian and Lunar regolith was successfully performed during this work by utilising laser‐based powder bed fusion equipment. Extensive evaluation of the raw regolith simulants was conducted via Optical and Electron Microscopy (SEM), Visible‐Near Infrared/Infrared (Vis‐NIR/IR) Spectroscopy and thermal characterisation via Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The analysis results led to the characterisation of key properties of these multicomponent ceramic materials with regards to their processability via powder bed fusion 3D printing.\ud The Lunar and Martian simulant regolith analogues demonstrated spectral absorbance values of up to 92% within the Vis‐NIR spectra. Thermal analysis demonstrated that these materials respond very differently to laser processing, with a high volatility (30% weight change) for the Martian analogue as opposed to its less volatile Lunar counterpart (<1% weight change). Results also showed a range of multiple thermal occurrences associated with melting, glass transition and crystallisation reactions. The morphological features of the powder particles are identified as contributing to densification limitations for powder bed fusion processing.\ud This investigation has shown that – provided that the simulants are good matches for the actual regoliths – the lunar material is a viable candidate material for powder bed fusion 3D printing, whereas Martian regolith is not