EXAFS, x-ray diffraction, and reverse Monte Carlo simulations of an amorphous Ni 60 Ti 40 alloy produced by mechanical alloying

The local atomic order of an amorphous Ni 6 0 Ti 4 0 alloy produced by mechanical alloying was studied by extended x-ray absorption fine structure (EXAFS) and x-ray diffraction (XRD) techniques. The experimental total structure factor derived from the XRD measurements was simulated by using the reverse Monte Carlo (RMC) method. This simulation was used to compute the S c N i - N i (K), S c N i - T i (K), and S c T i - T i (K) partial structure factors and to infer a three-dimensional structure for this alloy. The coordination numbers and interatomic distances for the first neighbors obtained from EXAFS and RMC showed a good agreement. The bond-angle distributions derived from the structure obtained by RMC simulations give evidence that the structure of amorphous Ni 6 0 Ti 4 0 alloy contains distorted trigonal-prismatic units. The calculated Warren chemical short-range order parameter showed a local chemical order similar to that one found in the solid solutions and in the Ni 3 Ti compound and different of that found in the NiTi compound.