The effect of cooling rate and grain size on hydride formation in Zircaloy-4

We explore the distribution, morphology and structure of zirconium hydrides formed using different cooling rates through the solid state Zr+[H] --> Zr + hydride transus, in fine and blocky alpha Zircaloy-4. We observe that cooling rate and grain size control the phase and distribution of hydrides. The blocky alpha (coarse grain, > 200 micrometer) Zircaloy-4, has a smaller grain boundary area to grain volume ratio and this significantly affects nucleation and growth of hydrides as compared to fine grain size (~11 micrometer) material.