Effect of flaws on the fracture behavior of structural ceramics
Fracture studies and nondestructive evaluation (NDE) were performed to detect and assess the effect of flaws on the fracture behavior of hot-pressed Si/sub 3/N/sub 4/ with Fe inclusions. The NDE methods used were through-transmission and backscatter ultrasound and low-kV contact radiography. The addition of 5 and 0.5 wt % Fe inclusions of 88 to 250 ..mu..m size reduced the strength of Si/sub 3/N/sub 4/ specimens by approximately 40 and 15%, respectively. Fractography indicated that failure occurred primarily from internal flaws which included Fe- and Si-rich inclusions and/or regions of Si/sub 3/N/sub 4/ matrix that were degraded as a result of reaction between Si/sub 3/N/sub 4/ and molten Fe. For Fe inclusion-induced internal flaws, the critical flaw sizes calculated by fracture mechanics were always larger than the fractographically measured flaw sizes. This observation suggested a local degradation in fracture toughness of Si/sub 3/N/sub 4/ matrix. A ratio, K, of approx.3.5 to 4.2 appeared to exist between the calculated and measured values of the critical internal flaw sizes. The ratio K will have important implications for strength prediction based on observed flaw size. A comparison of the fractography and NDE results for the location of critical flaws indicated that the backscatter ultrasound method may be more suitable than through-transmission ultrasound or low-kV contact radiography for the detection of near-surface flaws.
- Research Organization:
- Argonne National Lab., IL (USA)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 6480603
- Report Number(s):
- CONF-8705103-6; ON: DE87011432
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
ACOUSTIC TESTING
ALLOYS
DEFECTS
FABRICATION
FRACTOGRAPHY
FRACTURE PROPERTIES
HOT PRESSING
INCLUSIONS
INDUSTRIAL RADIOGRAPHY
IRON ADDITIONS
IRON ALLOYS
MATERIALS TESTING
MATERIALS WORKING
MECHANICAL PROPERTIES
NITRIDES
NITROGEN COMPOUNDS
NONDESTRUCTIVE TESTING
PNICTIDES
PRESSING
SILICON COMPOUNDS
SILICON NITRIDES
TESTING
ULTRASONIC TESTING
X-RAY RADIOGRAPHY