Structural Investigation of Noncrystalline Nickel‐Phosphorus Alloys

摘要

The structure of noncrystalline electrodeposited NiP alloys, 73.8–81.4 at.% Ni, has been investigated by x-ray scattering and by physical density measurements. The x-ray interference functions, I(k), are qualitatively inconsistent with those calculated for fcc-, hcp-, and Ni3P-type crystallites. Calculated radial distribution functions RDF(r) indicate that the alloys have a better defined short-range order than that observed in liquid noble metals above their melting points. The observed I(k) are very similar to the I(k) calculated by Dixmier, Doi, and Guinier [in Physics of Noncrystalline Solids, J. A. Prins, Ed. (North-Holland Publ. Co., Amsterdam, 1965), p. 67] from their model. However, the parameters needed to fit the experimental results are inconsistent with the atomic sizes expected for nickel and phosphorus. The noncrystalline alloys are between 0.6% and 1.4% less dense than the corresponding mixtures of fcc Ni and Ni3P, both of which are essentially close packed. A grain boundary density deficit model has been developed which relates the fractional density difference between the microcrystalline and macrocrystalline forms of a close-packed metal to the minimum average microcrystal grain size. The fractional density differences of between 0.6% and 1.4% observed for the noncrystalline NiP alloys would correspond to minimum average microcrystal grain sizes D of between 133 and 57 Å. Stored elastic energy calculations indicate that rms strains 2>1/2 greater than 0.03 and due to simple compressive and dilatory stresses are inconsistent with the reported energy of transformation of noncrystalline NiP to crystalline nickel and Ni3P. Crystallite size broadening with D≥57 Å and strain broadening with 2>^{1/2≤0.03 are insufficient to produce fcc, hcp, or Ni3P model I(k) consistent with the observed NiP I(k). The high densities of the noncrystalline NiP alloys suggest that the alloys have a continuous structure rather than one in which internal boundaries separate small well-ordered regions. These limitations on structural models for noncrystalline NiP alloys may apply to the other noncrystalline metallic alloys with similar diffraction patterns.}