Influence of dopant concentration on creep properties of Nd2O3-doped alumina

The microstructural features and tensile creep behavior of Al2O3 doped with Nd2O3 at levels ranging from 100 to 1000 ppm (Nd:AI atomic ratio) were sys tematically investigated. Compositional mapping, using both high-resolution scanning transmission electron microscopy and secondary ion mass spectrosc opy revealed that, for all of the compositions studied, the Nd3+ ions were strongly segregated to the Al2O3 grain boundaries, Microstructural observat ions revealed that the solubility of Nd2O3 was between 100 and 350 ppm, Ten sile creep tests were conducted over a range of temperatures (1200 degrees -1350 degreesC) and stresses (20-75 MPa). Both the stress and grain-size ex ponents were analyzed. In selected experiments, controlled grain-growth ann eals were used to enable creep testing of samples of the same average grain size but different neodymium concentrations. Independent of dopant level, the neodymium additions decreased the creep rate by 2-3 orders of magnitude , compared with that of undoped Al2O3. The value of the apparent creep acti vation energy increased with increased dopant concentration and then satura ted at dopant levels exceeding the solubility limit. Overall, the results o f the present study were consistent with a creep-inhibition mechanism where by oversized segregant ions reduce grain-boundary diffusivity by a site-blo cking mechanism.