INCOMMENSURATE SHEAR-WAVE UNDER UNIAXIAL-STRESS

A periodic shear wave (PSW), observed in gamma-Fe precipitates in Cu at low temperature, was studied by X-ray diffraction under compressive uniaxial stress within an elastic limit. Although the lattice structure has an orthorhombic symmetry, for the applied stress, each Fe precipitate behaves as if it possessed a tetragonal symmetry which is accomplished through the PSW formation. This indicates that the PSW is regarded as an intrinsic incommensurate lattice wave although the wavelength is mainly determined by the mesoscopic veriable, i.e., the size of the precipitates. The PSW is well explained by a new model of a precursor modulated phase in the martensitic transformation based on the nonlinear and nonlocal elastic continuum theory.