Codoping of alumina to enhance creep resistance

The tensile creep behavior of both singly and multiply doped alumina sample s has been investigated in order to understand better the impact of dopant segregation to grain boundaries on observed creep resistance. Previous stud ies have suggested that the segregation of time oversized dopant ions reduc es the grain boundary diffusivity and thus the creep rate. The aims of the present work are to examine the possibly beneficial effects of selective co doping 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 contai ning nominally (i) 100 ppm zirconium, (ii) 100 ppm neodymium, (iii) 100 ppm zirconium codoped with either 100, 350, or 1000 ppm neodymium, (iv) 100 pp m zirconium codoped with 1000 ppm scandium. Microchemical mapping using sec ondary ion mass spectrometry revealed direct evidence of cosegregation of t he dopant ions to grain boundaries. Tensile creep tests were carried out in the temperature range of 1200-1350 degrees C, utilizing stresses ranging f rom 20 to 100 MPa, In the case of the Nd/Zr codoped alumina, it was found t hat the creep rate decreased by 2 to 3 orders of magnitude relative to undo ped 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 resist ance was obtained for compositions both above and below the solubility limi t of Nd in alumina; hence the phenomenon is primarily a solid solution dete ct.