X‐Ray Microbeam Studies of Fracture Surfaces in Alumina

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Abstract
Studies using a double‐crystal X‐ray spectrometer to measure crystal distortion at various depths below the fracture surfaces of polycrystalline alumina have shown two zones of distortion. Zone I, of high distortion, extends about 10μ; zone II, having much lower distortion, extends over 50μ (in excess of one grain diameter). Both zones are observed in specimens fractured at 20° and at 1700°C. The primary difference observed between specimens broken at the two temperatures is that zone I has a much higher misorientation in the 1700°C fractures than in 20°C fractures; zone I1 is quite similar for the two temperatures. Since zone I appears in all reflections and is about one half grain diameter in depth, it is proposed that this distortion arises from basal and nonbasal slip in those grains through which the fracture crack passes. Since zone II is observed only in the (0330) and (2240) reflections, it is proposed that this distortion is the result of basal slip only. From these data the plastic work of fracture is estimated as about 1500 ergs per cm2. This estimate is probably high by 10 to 25%. The value for the work of fracture is relatively independent of temperature. The method described in this work permits study of the deformation in the thin layers near the fracture surface in any material.