Keynote Speaker
Prof. Xueqiang Cao
Wuhan University of Technology
E-mail: xcao@whut.edu.cn
Title: Stability of Thermal Barrier Coatings in Natural Environment
Profile:
Xueqiang Cao is a professor of Wuhan University of Technology. Professor Cao obtained his first PhD in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences in 1994, and obtained his second PhD in Ruhr Univ.-Bochum of Germany in 2004. Between 2001 and 2015, he worked in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, and obtained The National Science Fund for Distinguished Young Scholars in 2008. Since 2015, he works in Wuhan University of Technology. He focuses his work on new thermal barrier coating materials mainly containing rare earths for high temperature applications, more than 360 scientific papers and 2 books have been published. One of his paper which was published in Journal of the European Ceramic Society has been cited for 2050 times.
Abstract:
Thermal barrier coatings (TBCs) are usually composed of NiCrAlY as bond coat (BC) and yttria stabilized zirconia (YSZ) as top coat (TC). During storage of TBCs in natural environment, TBCs may be seriously corroded, and the corrosion mechanism is studied. On one hand, BC would be corroded by the residual Cl- in YSZ powder. The nano-powder of YSZ contains a lot of ZrOCl2 and YCl3, HCl is formed in moisture, leading to the corrosion of BC. The BC is also NiCrAlY alloy, with Al and Cr content higher than the substrate Ni-based high-temperature alloys, leading to about 50 mV lower corrosion potential for BC compared to the substrate, therefore, resulting in galvanic couple with the BC. The influence of different Al contents in NiAl alloys on their corrosion behavior in dilute H2SO4, simulating the corrosive environment was studied. The research demonstrates that a high Al content in the BC is the primary cause of corrosion in conditions of natural environment. On the other hand, the structural stabilizer Y3+ in YSZ would react with H2O in moisture, leading to the phase transformation of YSZ from the tetragonal to the monoclinic phase. A core/shell structure of ZrO2/Y2O3 in YSZ crystalline grains has been proved. Calcination of YSZ above 1100 ℃ can prevent the degradation.