FORMATION OF THE MONOCLINIC ALPHA''-PHASE IN QUENCHED U-3.6 AT.PERCENT TI-4.7 AT.PERCENT 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 electro n microscopy. It was found that in addition to the orthorhombic alpha' martensite a monoclinic alpha '' phase forms in the quenched material . The lattice parameters and the space group of the monoclinic alpha ' ' phase were determined by the Rietveld refinement method and then wer e verified by electron diffraction. The unit cell of the monoclinic st ructure was treated as a side-centered parallelepiped with the unique axis b. The space group was determined as C2/m and the lattice paramet ers were: a = 0.5838 nm, b = 0.2858 nm, c = 0.1973 nm and beta = 91.08 degrees. Orientation relationship between alpha' and alpha '' lattice s was determined from the analysis of the electron diffraction pattern s. It was shown that the formation of alpha' and alpha '' structures f rom the cubic gamma structure can be explained by the model similar to that suggested for U-Mo and U-Nb systems, and the alpha'/alpha '' ori entation relationship observed in the experiment excellently fit; this model. (C) 1997 Elsevier Science B.V.