“Everyone in the industry has been waiting for this discovery. This is a paradigm shift in the field of high-temperature oxidation. We are now establishing new principles for understanding the degradation mechanisms in this class of materials at very high temperatures.”
Many current and future technologies require alloys that can withstand high temperatures without corroding. Now, researchers at Chalmers University of Technology, Sweden, have hailed a major breakthrough in understanding how alloys behave at high temperatures, pointing the way to significant improvements in many technologies. The results are published in the highly ranked journal Nature Materials.
Developing alloys that can withstand high temperatures without corroding is a key challenge for many fields, such as renewable and sustainable energy technologies like concentrated solar power and solid oxide fuel cells, as well as aviation, materials processing and petrochemistry.
At high temperatures, alloys can react violently with their environment, quickly causing the materials to fail by corrosion. To protect against this, all high temperature alloys are designed to form a protective oxide scale, usually consisting of aluminium oxide or chromium oxide. This oxide scale plays a decisive role in preventing the metals from corroding. Therefore, research on high temperature corrosion is very focused on these oxide scales – how they are formed, how they perform at high heat, and how they sometimes fail.
The article in Nature Materials answers two classical issues in the area. One applies to the very small additives of so-called ‘reactive elements’ – often yttrium and zirconium – found in all high-temperature alloys. The second issue is about the role of water vapour.
Further to their discoveries, the Chalmers researchers suggest a practical method for creating more resistant alloys. They demonstrate that there exists a critical size for the reactive element particles. Above a certain size, reactive element particles cause cracks in the oxide scale, that provide an easy route for corrosive gases to react with the alloy substrate, causing rapid corrosion. This means that a better, more protective oxide scale can be achieved by controlling the size distribution of the reactive element particles in the alloy.