Zirconium-based alloys

Chemical Analysis of Zirconium and Zirconium-base Alloys, ASTM E 146-68, American Society for Testing and Materials, Philadelphia, Pa., 1969. 

Phase Transformations in Titanium- and Zirconium-Based Alloys... 

Non-equilibrium Processing of Materials edited by C. Suryanarayana Phase Transformations in Titanium- and Zirconium-based Alloys... 

The thermal absorption cross section of zirconium is the lowest of all mechanically strong, high-melting, corrosion-resistant metals. For this reason, zirconium and zirconium-based alloys are the materials preferred for cladding and structural materials in water-cooled, thermal-neutron power reactors. 

The grades of zirconium and zirconium-base alloys commercially available in the United States are described in ASTM Special Technical Publication 639 [S2]. The most important of these are zircaloy-2, zircaloy-4, and Zr-2.5 Nb. Table 7.4 gives the ASTM composition specifications for these three alloys and zirconium sponge. 

Zirconium-based alloys have received special attention, leading to the discovery, by Johnson group, " of several stable glasses and among them the complex composition (ZrsTOo,55 (Cu5Ni4)o,225660,225- This material called Vitreloy 1 (VI) is a commercial product used, for instance, for the fabrication of golf clubs. 

Vizcaino et al. developed a method to simultaneously measure hydrogen concentrations in zirconium-based alloys. The measurements provided both the temperature of terminal solid solubility and the heat of hydride dissolution, using a DSC. The hydrogen concentration measured widi that technique, and the values obtained wife a standard hydrogen gas meter, showed a linear relation with a correlation factor of 0.99 over the entire solubility interval in the ctZr phase. The authors suggested that the present method was especially appropriate for alloys where a partition of the overall hydrogen concentration in two phases exists, and is applicable to all hydride forming metals which ideally follow the van t Hoff law [29]. 

Zirconium-based alloys were among the first non-noble metal-based alloys found to solidify in the amorphous state upon cooling from the melt at corrparatively low rates R, such as 10 Ks [1.69,70]. The term bulk glassy alloys refers to the fact that this solidification behavior permits us to obtain bulky parts with an amorphous structure by conventional casting procedures, e.g., in rod form, up to 30 mm. Data are given in [1.71,72]. 

Exposure to fast neutron fluxes increases the corrosion rate of zirconium-based alloys. Even in the highly oxidizing environment of a BWR coolant, however, the corrosion rate of the principal zirconium alloys is low enough that cladding corrosion is not a limiting factor on the life of the fuel element. 

The use of organic coolant (terphenyl mixtures) in a D20-moderated system has been investigated in the Canadian WR-1 research reactor at Whiteshell, Manitoba. Experience has confirmed that zirconium-based alloys are suitable for extended operation in organic coolant provided there is careful control of the coolant chemistry to prevent excessive hydrogen uptake and fuel tube fouling. 

Fortunately, Bettis Atomic Power Lab already had an active program of corrosion tests for a number of zirconium-based alloys. Included was one ingot in which a small amount of stainless steel had accidentally been added. Test results revealed the beneficial effects of iron, nickel, and chromium. Quickly, zircaloy-2, the Zr-1.5% Sn-0.12% Fe-0.1% Cr-0.05% Ni, was developed and specified for the Nautilus reactor in August 1952. That reactor generated power on December 30,1954. The Nautilus got imderway on January 17,1955. This marked the beginning of a new era. 

Development of new zirconium alloys. An alloy development program was started at ORNL to find a radiation-corrosioii-resistant zirconium-base alloy with satisfactory metallurgical properties. These include weldability, strength, ductility, formability and stability. 

M. L. PiCKLE.siMEK, Anodizing as a Metallographic Technique for Zirconium Base Alloys, L SAEC Report ORNL-2296, Oak Ridge National Laboratory, 1957. 

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