Comparison among SANS Technique and Conventional Methods for Cavity Characterization in Superplastically Deformed Ceramic

Abstract

A novel small angle neutron scattering (SANS) method was applied for characterization of cavities in a 3Y-TZP subjected to superplastic deformations under different conditions, and the results were compared with conventional methods, i.e. SEM analysis and density measurement (Archimedes) method. Morphology of cavities formed in the 3Y-TZP specimens varied depending on the deformation condition and the dimension of the specimen. Effects of cavity morphology on the cavity characterization were investigated and were discussed for each method. It was found that: (1) The accuracy of the data obtained from SEM analysis was very sensitive to the morphology of cavities, while (2) Archimedes and SANS methods gave similar results, and showed good reliability for evaluation of bulk properties of cavities.

A Simple Method to Improve Superplastic Elongation and Strength of 3Y-TZP Deformed at High Strain-Rates

“…It is evident that this softening is not due to the formation of local necking but stems from another phenomena, because no obvious necking was identified on the specimens even after their fractures (see Fig. 2), The softening must, therefore, be caused by either or both of the followings : (1) The gradual decrease in the actural cross-sectional area of the specimen, sustaining applied load, due to the formation and concurrent growth of flat cavities during the deformation as has been described in our previous papers [8,10], and (2) the decrease in true strain-rate with the progress of the deformation, because the tensile tests are performed at constant cross-head speeds. It is, therefore, essential to obtain the true stress versus true strain relations under a constant true strain-rates condition.…”

“…As well known, cavities can be formed and grown in fine-grained polycrystalline materials subjected to superplastic deformation [1][2][3][4][5][6][7][8][9][10]. In tetragonal zirconia polycrystals (Y-TZP) pulled under high strain-rate superplastic condition, the formation of fine and crack-like flat cavities having very narrow gaps lying along grain boundaries mostly normal to the tensile axis has been found by means of a small angle neutron scattering (SANS) technique [7][8][9][10].…”

Influence of Flat Cavity Formation on Stress vs. Strain and Strain-Rate Relations of Superplastic Deformation in 3Y-TZP

“…The softening must, therefore, be caused by either or both of the followings: (1) The gradual decrease in the actural cross-sectional area of the specimen, sustaining applied load, due to the formation and concurrent growth of cavities, in particular, flat cavities during the deformation as has been described in our previous papers, [8][9][10] and (2) the decrease in a true strain-rate with the progress of the deformation, because the tensile tests are performed at constant crosshead speeds. It has been found 12) that even though the decrease in the true strain-rate with the deformation due to the constant pulling speed is taken into consideration, the strain softening appears on the stress vs. strain curves of the specimens deformed at high strain-rates.…”

“…[1][2][3][4][5][6][7][8][9][10] In tetragonal zirconia polycrystals (Y-TZP) pulled under high strain-rate superplastic condition, the formation of fine and crack-like flat cavities having very narrow gaps lying in grain boundaries mostly normal to the tensile axis has been found by means of a small angle neutron scattering (SANS). [7][8][9][10] The formation of these flat cavities seemed to be responsible for the strain softening that appeared on the true stress-strain curves.…”