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The continuous development of new industrial applications, such as sliding or ball bearings, cutting tools, etc., as well as elements protecting against ballistic impact (armours, bullet–proof vests, etc.), requires the increasing use of super–hard and ultra–hard ceramics as they excel for their resistance to wear and contact damage, high temperatures and chemically aggressive environments (oxidation, corrosion, etc.). On this basis, the scope of my research is focused on processing ceramic composites based on super–hard and ultra–hard phases (carbides, borides, carbonitrides, etc.).

During my PhD period I was involved on developing new ultra–hard composite ceramics based on B4C, with improved toughness. B4C has great potential since it has a singular low density (∼2.52 g/cm³) and superior hardness (≥30 GPa). However, its high melting point (∼2490 °C), and its inherent brittleness greatly hinders its manufacture and incorporation into these engineering areas. To solve these serious drawbacks, I added small proportions of certain additives to reduce the sintering temperature of the B4C without compromising its high hardness. I chose MoSi2 and Ti-Al as additives because during sintering they generate a transient liquid–phase, which first helps to densify and then reacts in situ with the B4C disappearing completely to give rise to other refractory and ultra–hard carbides and borides. In addition, to alleviate the problem of the brittleness of B4C, I also manufactured ultra–hard and toughened materials incorporating carbonaceous nanoplatelets as reinforcements that hinder the propagation of cracks. All materials were ultra–fast densified by spark plasma sintering (SPS) with or without pressure. Furthermore, I prepared many powder mixtures used for SPS with pressure following an environmentally friendly route by aqueous colloidal processing, which was also the technique that I used for preparing the green parts with near–net–shape for presureless SPS.

At present I have a Postdoctoral Fellowship that is being held at the University of Aveiro until the end 2023 and it will continue at the University of Seville during 2024. Throughout 2023, the approach that I am taking aims at combining super–hard and ultra–hard ceramics (TiCN, cBN) with small amounts of reactive sintering additives that have not been used before to be ultra–fast densified at lower temperatures. Once the manufacturing step has been completed, I am evaluating the potential of these new ceramic composites by microstructural and mechanical characterization, and I am also performing systematic electrochemical studies to test their corrosion resistance. This workplan will be also followed over 2024 with a new family of materials as the aim during the whole period consists of developing novel super–hard and ultra–hard ceramics which are excellent candidates to be implemented in the abovementioned industrial applications.

Dr. Cristina Ojalvo Guiberteau 
“Margarita Salas” Postdoctoral Fellow

cristinaog@unex.es

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