Relationship between crystallographic texture and dilatometric behaviour of a hexagonal polycrystalline material

The main objective of the present paper is to describe the relationship between the texture of polycrystalline samples having hexagonal lattice symmetry with their dilatometric behaviour during continuous healing. For this purpose, a thick Zr base alloy tube (Zr>98%) has been used. The initial texture of the tube was characterised by x-ray diffraction techniques using pole figures and the Orientation Distribution Function (ODF), The experimental results highlight a strong influence of the cutting direction of samples on the dilatometric behaviour. Introducing the single crystal Coefficients of Thermal Expansion (CTE) obtained from the literature, and using the coefficients of the spherical harmonics development of the ODF, it has been possible to calculate the CTE of textured polycrystals in the alpha phase field along any direction of the sample. The calculated CTE compare quite well with the experimental ones. Moreover, for alloys with a typical alpha grain size of 15 mu m in diameter, the experimental dilatometric contraction/dilation associated with the alpha to beta phase transformation upon heating has been correlated to the CTE in the alpha-phase field and can therefore be correlated to the initial texture.