Scanning electron-acoustic microscopy of MgO crystals

Abstract

The capability of scanning electron-acoustic microscopy in the characterization of MgO crystals has been studied. The conditions for the observation of different surface and subsurface features in as-grown and deformed crystals are described and the results are discussed on the basis of thermal and nonthermal mechanisms of acoustic signal generation.

Microstress Contrast in Scanning Electron Acoustic Microscopy of Ceramics

“…(16) predicts that regions of predominantly tensile strain (positive 11) should produce a fractional change in acoustic output signal that is opposite to that produced in regions of predominantly compressive strain (negative 11). In our SEAM examination of Vickers indentations in both SiC whisker-reinforced alumina and soda-lime glass [17], we fmd this to be the case.…”

“…(4) as (15) Variation in acoustic output signal as a function of strain From Eqs. (4), (13) and (14) we fInd the fractional change in the acoustic output signal due to strain in the material to be (16) Since Eq. (16) provides a means of directly comparing the effects of strain fields in the material with relative variations in the acoustic signal generated by the chopped electron beam, it also provides a means of directly assessing SEAM image contrast due to such fields.…”

“…Although SEAM has been applied to the characterization of a wide variety of materials [7][8][9][10][11][12][13][14][15], only recently has it been applied to the assessment of brittle materials [16,17]. We have found [17] that SEAM images of Vickers indentations of SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to assess the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter.…”