Self-Healing Metallo Ceramics

This year’s conference has a line-up of exceptional speakers; below Professor Sybrand van der Zwaag from the Novel Aerospace Materials Group  (www.novam.lr.tudelft.nl), at the Faculty of Aerospace Engineering, TU Delft, The Netherlands, gives a preview of his presentation at the conference on ‘ Self-healing in metallo-ceramics and the evelopment of new metallo-ceramics based on minor elements’.

The aim of the research of the Novel Aerospace Materials Group (NovAM) in Delft is to come up with new material concepts which will give new functionalities, meaning they could be relevant to future aircraft and spacecraft. As the range of materials and functionalities in aircraft and spacecraft is very large, the NovAM group is a truly multi-material group working on many new lines in materials. We focus  on four research lines:

1. the design and synthesis of new polymers for high temperature and space applications, robust organic solar cells and membranes,
2. the computational design of new high performance steels and titanium alloys for landing gear, drive shafts and blades for turbine engines,
3. the development of flexible sensors and actuators based on topologically structured piezo and pyroelectric ceramics granulates in well chosen polymer matrix and finally;
4. the development of self–healing materials.

EBSD measurement of an oxidatively healed crack in Ti₂AlC

Self-healing materials are capable of healing microscopic cracks spontaneously by a so-called healing reaction. Our self-healing material can be a polymer, a composite, a metal or a ceramic or even a metallo-ceramic. Clearly each material class has its own design and healing strategy.

One of the most interesting self-healing materials we explore are metallo-ceramic MAX phases. Metallo-ceramics are a relatively new form of matter with interesting properties between those of metals and ceramics. More or less by chance we discovered that Ti₃AlC₂ and Ti₂AlC are self-healing when exposed to high temperatures (1000-1200 ⁰C) in air.  Cracks which form are filled by special oxides which make the material regain its strength (see the figure to the right).  We have done extensive research on the synthesis of these materials via Spark Plasma Sintering, as well as their healing mechanisms and kinetics. In my talk I will show you some interesting results from these experiments.

Recently we became interested in the question of whether other MAX phases with higher melting and use temperatures would also be self healing, and from this we developed a predictive theory. This theory predicts that there are also MAX phases based on minor elements which should be self healing. I will present these predictions at the MMTA Conference, and I hope that we can establish contact with interested delegates to come together for the first trials to make and test such materials, initiating their industrial development.

Professor Sybrand van der Zwaag holds an MSc in metallurgy from the TU Delft and a Phd in applied physics from Cambridge University. He has worked for 10 years in the high performance fibre industry, before returning to the university.  Since 1992 he has held the chair   Microstructure Control in Metals and since 2004 the chair Novel Aerospace Materials.  He has published over 450 journal articles in various fields of materials science.  In 2014 he was awarded the title of distinguished professor due to his scientific research on industrially relevant materials and his promotion of better interactions between industry and academia.