Codoping of Alumina to Enhance Creep Resistance

• Published in: Journal of the American Ceramic Society Vol. 82; no. 6; pp. 1497 - 1504
• Main Authors: Li, Yan-Zun, Wang, Chongmin, Chan, Helen M., Rickman, Jeffrey M., Harmer, Martin P., Chabala, Jan M., Gavrilov, Konstantin L., Levi-Setti, Riccardo
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01.06.1999; Blackwell; Wiley Subscription Services, Inc
• Subjects: Condensed matter: structure, mechanical and thermal properties; Creep; Defects and impurities in crystals; microstructure; Doping and impurity implantation in other materials; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Grain and twin boundaries; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; Solubility, segregation, and mixing; phase separation; Structure of solids and liquids; crystallography; Grain boundaries; Inorganic compounds; Creep; Segregation; Experimental study; Scandium additions; Zirconium additions; Neodymium additions; SEM; SIMS; Microstructure; Codoping; Aluminium oxides
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1999.tb01947.x

The tensile creep behavior of both singly and multiply doped alumina samples has been investigated in order to understand better the impact of dopant segregation to grain boundaries on observed creep resistance. Previous studies have suggested that the segregation of the oversized dopant ions reduces the grain boundary diffusivity and thus the creep rate. The aims of the present work are to examine the possibly beneficial effects of selective codoping in enhancing creep resistance, and to elucidate the role (if any) of precipitates in creep inhibition. The specific singly and codoped systems considered in this work were as follows: hot‐pressed alumina samples containing nominally (i) 100 ppm zirconium, (ii) 100 ppm neodymium, (iii) 100 ppm zirconium codoped with either 100, 350, or 1000 ppm neodymium, (iv) 100 ppm zirconium codoped with 1000 ppm scandium. Microchemical mapping using secondary ion mass spectrometry revealed direct evidence of cosegregation of the dopant ions to grain boundaries. Tensile creep tests were carried out in the temperature range of 1200‐1350°C, utilizing stresses ranging from 20 to 100 MPa. In the case of the Nd/Zr codoped alumina, it was found that the creep rate decreased by 2 to 3 orders of magnitude relative to undoped alumina. This improvement was greater than that achieved by doping with either Nd or Zr alone, and demonstrates that the incorporation of ions of differing sizes may be beneficial. The observed enhancement in creep resistance was obtained for compositions both above and below the solubility limit of Nd in alumina; hence the phenomenon is primarily a solid solution effect.