Diffusion-induced solid-state amorphization (SSA) was studied in (fcc Ni)/(hcp Ti) multilayers at 523 K. The multilayers had a modulation length of 24.4 nm and an overall composition of Ni4OTi«.They were polycrystalline without coherency between the Ni and Ti sublayers. The phase changes, composition changes, and strain development were studied for annealing times up to 220 h, primarily using x-ray-diffraction methods. Upon annealing, an amorphous phase developed, concurrently with dissolution of Ti in crystalline Ni. The amorphous phase not only formed along the Ni/Ti interfaces, but also along the grain boundaries in the sublayers. Continued amorphization along the original grain boundaries on prolonged annealing implies that fast-diffusion paths in the amorphous phase remained active. Diffusion coefficients were determined, using methods described in a separate paper. The interdiffusion coefficient for the amorphous phase is smaller than the tracerdiffusion coefficient of Ni in hcp Ti and larger than the chemical diffusion coefficient in fcc (Ni, Ti) solid solutions. The reaction virtually stopped after 16 h, when appreciable amounts of crystalline Ni and Ti were still present, which is ascribed to ordering in the crystalline (Ni, Ti) solid solution.Both the dissolution of Ti in crystalline Ni and the amorphization are associated with the development of stress profiles in the multilayer. These are quantitatively discussed and analyzed using the x-ray-diffraction and Fizeau interferometric data.

A simple yet robust algorithm is presented to approximate data containing noise by smooth spline functions. The method is easy to implement and fast. Experience has shown that in the great majority of cases no user decisions are required to obtain adequate approximants, which is a useful property for routine processing of experimental data. The statistical basis of the algorithm is a generalized version of the Durbin–Watson statistic, which performs well even in the presence of correlated noise. Examples are given to illustrate the power of the algorithm. © 1998 American Institute of Physics.

Diffusion-induced phase transformations were studied in Ni//3-Ta multilayers between 523 K and 823 K, primarily using x-ray diffraction. The multilayers had a modulation length, A, of 20.3 nm and a composition of Ni 48 Ta 52 . They were polycrystalline without coherency between the Ni and Ta sublayers. Upon annealing at relatively low temperatures (up to 723 K) Ta dissolved in crystalline Ni, concurrently with the formation of an amorphous phase. The interdiffusion reactions did not take place only at the Ni/Ta interfaces, but also along the grain boundaries in the sublayers. The chemical diffusion coefficient in the amorphous phase was determined at 673 K, using a previously developed method. The results were compared with experiments on Ni/Ti multilayers, which show similar reactions. At 723 K and higher temperatures the fee (Ni, Ta) solid solution transformed into the stable Ni 3 Ta compound.

Using a columnar approximation, the effect of random layer thickness variations in a compositionally modulated material on the x-ray diffraction pattern is expressed in terms of their distribution function. It is demonstrated that the Fourier transform of this distribution function appears in a function describing the effective phase relations between the individual layers. Features of multilayer diffraction patterns, such as the presence or absence of superlattice peaks, are explained. It is also shown that when the Fourier transform of the thickness variation distribution changes sign from positive to negative, the superlattice peaks change position from integral to half-integral order. The effects of thickness variations are compared with those of interface roughness.

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