, Volume 43, Issue 3, pp 806-821
Date: 08 Oct 2011

Crystallographic Texture and Volume Fraction of α and β Phases in Zr-2.5Nb Pressure Tube Material During Heating and Cooling

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Abstract

The phase transformations in an as-received Zr-2.5Nb pressure tube material were characterized in detail by neutron diffraction. The texture and volume fraction of α and β phases were measured on heating at eight different temperatures 373 K to 1323 K (100 °C to 1050 °C) traversing across the α/(α + β) and (α + β)/β solvus lines, and also upon cooling at 1173 K and 823 K (900 °C and 550 °C). The results indicate that the α-phase texture is quite stable, with little change in the {0002} and \( \left\{ {11\bar{2}0} \right\} \) pole figures during heating to 1123 K (850 °C). The β-phase volume fraction increased while a slight change in texture was observed until heating reached 973 K (700 °C). On further heating to 1173 K (900 °C), there appears a previously unobserved α-phase texture component due to coarsening of the prior primary α grains; meanwhile the transformed β-phase texture evolved markedly. At 1323 K (1050 °C), the α phase disappeared with only 100 pct β phase remaining but with a different texture than that observed at lower temperatures. On cooling from the full β-phase regime, a different cooldown transformed α-phase texture was observed, with no resemblance of the original texture observed at 373 K (100 °C). The transformed α-phase texture shows that the {0002} plane normals are within the radial-longitudinal plane of the pressure tube following the Burgers orientation relationship of (110)bcc//(0002)hcp and \( [\bar{1}11]_{\text{bcc}} //[11\bar{2}0]_{\text{hcp}} \) with a memory of the precursor texture of the primary α grains observed on heating at 1173 K (900 °C).

Manuscript submitted February 24, 2011.