Codoping of Alumina to Enhance Creep Resistance

Abstract

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.

Creep mechanisms of laminated alumina/zirconia-toughened alumina composites

“…A similar effect has been found with other dopant cations. [22][23][24] Therefore, the stress level at which the alumina layers are submitted in the laminate corresponds to a low-stress damage-tolerant regime, as experimentally observed.…”

Microwave dielectric properties of Al2O3 ceramics co-doped with MgO and Nb2O5

“…. Considering the charge compensation effect reported by early literatures [20][21][22], this solid solubility could be further increased when Mg 2? /Nb 5?…”

Hot Superplastic Powder Forging for Transparent nanocrystalline Ceramics

“…It appears then that ZrO 2 on either side of the grain boundary migrate to the grain boundary. In cases where there was either no denuded zone or only a slight denuded zone, it is possible that ZrO 2 is supersaturated in the Al 2 O 3 matrix after quenching and especially near grain boundaries 20 , came out of solution between 1250 and 1350° C. The thermodynamic driving force for segregating to the grain boundaries is to minimize interface energy. Chen The role of the borosilicate glass is to enhance the kinetics of microstructure development, presumably by enhancing both grain boundary and bulk diffusion due to aliovalent ions.…”