Depth profiling of a functionally graded alumina/calcium-hexaluminate composite using grazing incidence synchrotron-radiation diffraction

Grazing incidence synchrotron radiation diffraction (GISRD) has been successfully used for near-surface depth profiling of phase composition, texture and residual strains in a functionally-graded alumina/calcium-hexaluminate (CA6) composite prepared by infiltration process. Depth profiling of near surface information both in the nanometre and micrometre ranges have been done by using angles of incidence below and above the critical angle (αc) for total external reflection. The penetration depth increased to several hundred angstroms as α approached αc. Above αc there was a rapid increase in penetration depth to a thousand angstroms or more. As the penetration depth increased the intensity of CA6 peaks relative to those of alumina became less intense, indicating a distinct gradation in the phase abundance. The distribution of CA6 grains at the near-surface was highly textured and showed a distinct depth-dependent gradation in texture. The presence of graded residual strains in the composite due to thermal expansion mismatch between the phases has been computed and verified from the display of line shifts. The unique but powerful capability of GISRD as a complementary tool for depth profiling the near-surface information of graded materials has been demonstrated in this work.