Aluminium cladded Al-U alloys are used as fuel in water cooled nuclear research reactors. The equilibrium microstructure of such an alloy consists of hard and brittle UAl4 particles uniformly dispersed in Al matrix. Addition of a small amount of Zr ( ~ 3 wt%) to Al-U alloys stabilizes the cubic and more desired UAl3 phase at room temperature which makes these alloys more amenable to hot rolling and reduces the tendency for the formation of microcracks and dog boning. In this paper the elastic constants of binary Al-10%U, Al-16%U and Al-22%U and ternary Al-8%U-1%Zr, Al-16%U-1%Zr, Al-22%U-2%Zr, Al-30%U-2%Zr and Al-46%U-3%Zr alloys (all composition in wt%) were evaluated by ultrasonic technique. These alloys were prepared by conventional melting and casting route, followed by hot rolling into plates of 7 mm thick. Samples of about 25 mm square were cut from these plates and used for this study. The longitudinal and transverse sound velocity of these alloys were measured along the direction perpendicular to rolling using a piezo electric probe of frequency 5 MHz. The velocity was measured with an accuracy of ±1 m/s. At least 10 readings were taken on each of the above mentioned alloy and their average value were reported. The elastic constants like Youngs Modulus and shear modulus was found to increase with increase in U content or with the volume fraction of UAl3/UAl4 phase. The Youngs Modulus varied from 71.6 GPa for Al-16%U to 91.6 GPa for Al-46%U-3%Zr alloy. The knowledge of modulus is very important to understand the mechanical behaviour such as creep since normalized stress (
/G) is used in a standard creep equation. Although the modulus values of binary alloys are reported in the literature [1], the modulus values of ternary Al-U-Zr alloys are reported for the first time in this study. Since Al-U alloys are fabricated in the form of plates of around 1 mm thick, they should have good ductility and resistance to cracking. The ratio of Shear to bulk modulus (G/K) values gives a very simple but generally successful, classification of inherently brittle and ductile metallic crystals [2]. The metals are ductile when G/K < 0.4 and considered brittle when G/K > 0.5. The G/K criterion has been used to classify Al-U and Al-U-Zr alloys with different U contents as ductile and brittle. It was found alloys containing low U contents has satisfied the G/K criterion of < 0.4, but Al- 46%U-3%Zr showed G/K values 0.45, which indicates these alloys are not truly ductile. This paper presents the experimental details of ultrasonic evaluation of elastic constants of Al-U and Al-U-Zr alloys and the analysis of the results. REFERENCES
- S. Nazar, G. Ondracek and F. Thummler, KFK report - 1252, Karlsruhe, 1970
- A. H. Cottrell, " Ductile Aluminium and Brittle Trialuminides". Mat. Sci. Technol., Vol. 7, pp. 981-983, 1991
NDTnet
