Technically-Pure and Low-Alloy Zirconium Materials

Only two zirconium materials are standardised Zr 702 which is essentially technically-pure Zr and consists of the a phase only, and Zr 705 which contains 2 to 3 wt% Nb, has ana + p microstructure and a higher yield stress. Their composition ranges and mechanical properties are listed in Tables 3.1-35 and 3.1-36. Since Hf is usually contained in the Zr ore zircon (ZrSiOa) and is difficult to separate, the Zr materials are specified to contain Hf up to 4.5 wt%. The presence of Hf in Zr alloys up to this level of composition does not affect the mechanical and corrosion properties significantly. 

The Zr-Nb phase diagram (Fig. 3.1-91) indicates that a + p microstructures can be obtained at the 2-3 wt% Nb level. This leads to both substitutional solid solution strengthening and dual phase strengthening effects. Oxygen has a high interstitial solubility in a-Zr. Fig. 3.1-92 shows the Zr-O phase diagram. It is inter- 

Common designation ASTM/UNS designation Zr702 R60702 Zr705 R60705 

Extensive data and references are available on the corrosion behavior of Zr in many types of media and under various conditions of exposure [1.67]. 

The irradiation effects on the mechanical properties are significant. The interstitial atoms and vacancies resulting from irradiation-induced atomic displacements give rise to the formation of dislocation loops of interstitial and vacancy type. These dislocation loops act as obstacles to slip dislocations and lead to an increase in yield stress and decrease in elongation upon fracture as a function of dose, as shown in Fig. 3.1-93. The effect saturates at about 10 nm .  

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