Influence of Dopant Concentration on Creep Properties of Nd2O3-Doped Alumina

The microstructural features and tensile creep behavior of Al 2 O 3 doped with Nd 2 O 3 at levels ranging from 100 to 1000 ppm (Nd:Al atomic ratio) were systematically investigated. Compositional mapping, using both high-resolution scanning transmission electron microscopy and secondary ion mass spectroscopy revealed that, for all of the compositions studied, the Nd 3+ ions were strongly segregated to the Al 2 O 3 grain boundaries. Microstructural observations revealed that the solubility of Nd 2 O 3 was between 100 and 350 ppm. Tensile creep tests were conducted over a range of temperatures (1200°-1350°C) and stresses (20-75 MPa). Both the stress and grain-size exponents were analyzed. In selected experiments, controlled grain-growth anneals 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 Al 2 O 3 . The value of the apparent creep activation energy increased with increased dopant concentration and then saturated at dopant levels exceeding the solubility limit. Overall, the results of the present study were consistent with a creep-inhibition mechanism whereby oversized segregant ions reduce grain-boundary diffusivity by a site-blocking mechanism.