Texture-Property Relationships in the Uranium-2.4 Weight Percent Niobium Alloy

摘要

Because the distances between atoms vary with direction within a crystal, the properties of a crystal also vary with direction. Such property variations are called crystalline anisotropy, and the amount of anisotropy depends on the symmetry of the crystal structure. The alpha-phases of uranium depends on the symmetry of the crystal structure. The alpha-phases of uranium and uranium alloys are of orthorhombic symmetry and, thus, are highly anisotropic. Normally, uranium and uranium alloys consist of polycrystalline aggregates (grains) whose crystal axes are orientated randomly with respect to each other; however, mechanic deformation can align preferentially the crystal axes of the grains to form a textured structure. In particular, forward extrusion of the uranium-2.4 wt % niobium alloy aligns the a axis of the alpha-phase parallel to the extrusion direction and the b axis transverse to the extrusion direction. Axis-density distribution charts show that the texture of the uranium-2.4 wt % niobium alloy is a function of the extrusion ratio. The linear thermal expansion of the uranium-2.4 wt % niobium alloy is reduced transverse to the extrusion direction and is increased parallel to the extrusion direction. The effect of anisotropy on tensile properties also is discussed. It is concluded that the properties of mechanically deformed, alpha-phase uranium and uranium alloys depend on the texture. (ERA citation 08:010259)