Ultrasonic Study of the Beta-to-Omega Phase in Zr-Nb Alloys.
CORNELL UNIV ITHACA N Y DEPT OF MATERIALS SCIENCE AND ENGINEERING
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Elastic constant, ultrasonic attenuation and x-ray measurements were made as a function of temperature on Zr-Nb single crystals in order to study the mechanism of the Beta to Omega phase transformation. In the Zr-20 wt. pct. Nb alloy C sub 44 decreased with decreasing temperature starting at 330-340K reaching a minimum at 160K, while both C and C sub 11 showed a positive deviation from linear quasiharmonic behavior starting at 250-280K. These observations are reversible with temperature. X-ray measurements indicated that little if any Omega phase was present in the 20 wt. pct. Nb alloy at 300K and that upon cooling to 89K a small amount of Omega was formed. It was suggested that the positive deviation of C sub 11 and C from the extrapolated values based on quasiharmonic theory is due to the presence of the Omega phase and that the onset of the Beta to Omega phase and that the onset of the Beta to Omega transformation is indicated by the first sign of deviation from linearity. The negative deviation of C sub 44 from quasiharmonic behavior is attributed to a softening of the b.c.c. structure which is a precursor to the actual transformation. The observations on the Zr-25 wt. pct. Nb alloy are in general agreement with these suggestions. In the Zr-30 wt. pct. Nb alloy the x-ray results indicated that no Omega phase is present over the temperature range 89-300K and C sub 11, C and C sub 44 all showed a normal linear variation with temperature, in agreement with the above suggestions. Author
- Properties of Metals and Alloys