Influence of hydrogen content on microstructure and crystallographic orientation of hydrides in recrystallized Zr-Sn-Nb tubes

Abstract:

Although there are many studies on the hydrides in Zirconium alloys, the microstructure and crystallographic orientation of hydrides with higher hydrogen content has received little attention. The Zr-Sn-Nb alloy charged with 147, 340 and 1480 ppm of hydrogen by gaseous hydriding procedure at 400 ℃ with different holding time. The microstructure and crystallographic orientation of hydrides is investigated by a combination of optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The results indicate that the orientation is affected by the hydrogen content. The interphase boundary components are used to evaluate the crystallographic orientation of hydrides along with pole figure analyses. We found that there are two orientation relationships between the α-Zr and the hydrides, i.e. (0001)α∥{111}δ and {10-17}α∥{111}δ. EBSD analyses also revealed changes in the orientation of hydrides when hydrides grew from one matrix grain to another to accommodate the matrix modification. Besides, there are many Zr grains with both inter-granular and intra-granular hydrides, and only the intra-granular hydrides exhibit habit relationships with the Zr grains.

Key words:Zr alloy; hydride; crystallographic orientation; habit plane; hydrogen content