Experimental investigation of the U-Zr-Al ternary phase diagram: Isothermal sections at 673 K and 1073 K.
Résumé
Isothermal sections at 673 K and 1073 K of the ternary U-Zr-Al system were established in the whole concn. range, by means of powder X-ray diffraction, SEM-energy dispersive X-ray spectroscopy and DTA. All measured compns. and unit-cell refinements were performed at room temp. from quenched samples annealed at 1073 K and 673 K for four and eight weeks resp. For both temps., the Al-rich corner of the phase diagram is characterized by extended homogeneity ranges due to mutual exchange between U and Zr in UAl3 (cubic, AuCu3-type) and in the Laves phase UAl2 (cubic, MgCu2-type). Minute U soly. in ZrAl2 (hexagonal, MgZn2-type) and in Zr2Al (hexagonal, Ni2In-type) was evaluated to be of the order of 1 at.% U. For the other binary compds., the soly. of the third component was found negligible. At 1073 K, the solid soln. based on γU (cubic, W-type) which covers the U-Zr binary axis up to 95.5 at.% Zr, allows also some limited soly. of Al [max. of 5 at.%]. For Al-content below 66 at.%, most of the phase relations comprise equil. between the Zr-Al binaries and the γ(U,Zr,Al) solid soln. At 673 K, the U-Zr axis is found in agreement with the literature data and no Al soly. could be detected in αU, αZr and UZr2 (δ phase). The phase relations are mainly established between Zr-Al binaries and αU. For monolithic UMo fuel with a Zr diffusion barrier foil cladded with Al, the main interaction product is expected to involve the U-based alloy with the Zr-Al binary compds. and the pseudo-binary U1-xZrxAl2 and U1-xZrxAl3 phases.