Formation of the monoclinic α′′ phase in quenched U-3.6 at.% Ti-4.7 at.% W alloy

The effect of quenching on the structure of ternary U-3.6 at.% Ti-4.7 at.% W alloy was studied by X-ray diffraction and transmission electron microscopy. It was found that in addition to the orthorhombic α′ martensite a raonoclinic α″ phase forms in the quenched material. The lattice parameters and the space group of the monoclinic α″ phase were determined by the Rietveld refinement method and then were verified by electron diffraction. The unit cell of the monoclinic structure was treated as a side-centered parallelepiped with the unique axis b. The space group was determined as C2/m and the lattice parameters were: a = 0.5838 nm, b = 0.2858 nm, c = 0.4973 nm and β= 91.08°. Orientation relationship between α′ and α″ lattices was determined from the analysis of the electron diffraction patterns. It was shown that the formation of α′ and α″ structures from the cubic γ structure can be explained by the model similar to that suggested for U-Mo and U-Nb systems, and the α′/α″ orientation relationship observed in the experiment excellently fits this model.