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X-ray Topography Study of Surface Damage in Single-Crystal Sapphire

Published online by Cambridge University Press:  10 February 2011

D. Black ,
R. Polvani ,
K. Medicus  and
H. Burdette
D. Black
Affiliation:
NIST, Gaithersburg, MD 20899, david.black@nist.gov
R. Polvani
Affiliation:
NIST, Gaithersburg, MD 20899, david.black@nist.gov
K. Medicus
Affiliation:
NIST, Gaithersburg, MD 20899, david.black@nist.gov
H. Burdette
Affiliation:
NIST, Gaithersburg, MD 20899, david.black@nist.gov
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Abstract

X-ray diffraction topography was used to investigate the relationship between subsurface damage, near-surface microstructure, and fracture strength in a series of sapphire modulus of rupture (MOR) bars which had been fabricated to proof test fabrication processes. The strength of the bars was determined by failure in four point bending. The tensile surface of the bars was also examined using optical microscopy and non-contacting surface profilometry. Both show that the bars have good surface finish, with a typical RMS roughness of 0.7 nm. No correlation was found between RMS surface finish and fracture strength. Although the bars appeared to be indistinguishable, topographs taken prior to fracture testing revealed that they are of two distinct types. Type 1 has an oriented microstructure consisting of a pattern of linear features running the length of the bars. Type 2 was typical of well-polished sapphire, containing individual dislocations and occasional damage from handling. We attribute the Type 1 microstructure to fabrication damage that was not removed by subsequent processing and/or polishing. Fracture strength data showed that the Type I (damaged) bars had strengths less than 70 % of the bars without damage. Topography is sensitive to near-surface damage that can be correlated to fracture strength. Neither low magnification optical microscopy nor conventional surface finish statistics could be correlated to strength.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 590: Symposium R – Applications of Synchrotron Radiation Techniques…V , 1999 , 279
Copyright
Copyright © Materials Research Society 2000

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References

REFERENCES

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