The Influence of Titania on Creep in Superplastic Zirconia

Abstract

Detailed high‐temperature compression creep experiments on a pure 3 mol% yttria‐stabilized tetragonal zirconia (3YTZ) and 3YTZ doped with 4.8 wt% TiO2 revealed that both materials exhibit a similar transition in stress exponents from n∼1 to n∼2 with a decrease in stress. The stress exponent of 1 and the inverse grain size dependence p of ∼3 are consistent with the Coble diffusion creep at high stresses; the increase in stress exponent at low stresses is attributed to an interface‐controlled diffusion creep process. Measurements revealed that grain‐boundary sliding contributes to >∼50% of the total strain in both regions with n∼1 and n∼2, indicating the operation of the same fundamental deformation process in both regions. The creep data indicate that doping with TiO2 leads to an increase in the grain‐boundary diffusion coefficients. The increase observed in the dihedral angle with doping is also consistent with the increase in grain boundary diffusion coefficient and the reported enhanced ductility in such materials.

The contribution of grain boundary sliding in tensile deformation of an ultrafine-grained aluminum alloy having high strength and high ductility

“…As also performed in this study, the vertical components of the sliding vector, hvi, were then calculated by subtracting the topographic profiles measured before and after tensile or compressive deformation. These earlier studies used one of two approaches to calculate hvi by measuring either (1) the topographic profile over the same set of grains [42,45] or (2) the topographic profile over similar but different sets of grains [29,30,41,43,44,46]. The first method is direct and also provides information on grain rotation and cavity nucleation and growth.…”

“…Using AFM to determine the role of GBS in samples deformed to high strains Most of the earlier studies examined the role of GBS by using AFM in the contact mode to evaluate the surface profile after testing [29,30,[41][42][43][44][45][46]. As also performed in this study, the vertical components of the sliding vector, hvi, were then calculated by subtracting the topographic profiles measured before and after tensile or compressive deformation.…”

“…The use of AFM has been successful in measuring the contributions of GBS in several investigations [29,30,[41][42][43][44][45] including grains as small as *50 nm [46]. Nevertheless, in all investigations involving AFM, especially when the material was not processed through SPD, the grain boundaries after small amounts of deformation, usually in the range from *10 to 20 %, were clearly discernible and therefore the height profiles provided direct information on the sliding offsets.…”

“…However, this marker line method is not easily adapted for use with UFG metals because the grain sizes are generally of the same order as the widths of the lines and this leads to ambiguities in determining the magnitudes of GBS. Alternative procedures are now available and these include surface profiling using an atomic force microscope (AFM) [29,30,[41][42][43][44][45][46], crosssectional examination in a scanning electron microscope (SEM) after preparation with a focused ion beam [36,37], and orientation imaging microscopy (OIM) conducted in situ within an SEM [47]. For both the AFM and OIM techniques, the sample surface is initially carefully polished and then examined after tensile or compressive testing in order to determine any differences that are introduced due to the deformation.…”

Review: Overcoming the paradox of strength and ductility in ultrafine-grained materials at low temperatures

“…11 Schematic illustrations in isometric and side and top views showing the configurations of two neighboring grains, 1 and 2, a before and b after GBS in response to an applied axial stress: the bold lines represent marker lines drawn parallel to the applied stress which incur sharp offsets at grain boundaries equal to v i and w i on the side and top surfaces, respectively, due to the occurrence of GBS [62] at the grain boundaries. In practice, it is feasible to use AFM or SEM to measure v j with the high accuracy that is needed in order to measure the very small offsets in NC and UFG materials [62,67,69,[71][72][73].…”