THE STRUCTURE OF EQUIATOMIC NITI, CUTI, NIZR AND CUZR PREPARED BY MECHANICAL ALLOYING

Amorphous powders of Ni50Ti50, Cu50Ti50, Ni50Zr50, and Cu50Zr50 were prepared by mechanical alloying of elemental powders in a Spex 8000 high-energy mixer/mill for 24 h. The structure of the alloyed powder was characterized using X-ray and neutron diffraction techniques. The X-ray patterns of the milled samples indicated that the mechanical alloys were amorphous, and that they were similar to corresponding alloys prepared by melt-spinning and by proton irradiation. The total X-ray structure factor [S(Q)]x is dominated by the topological short-range order (TSRO). The S(Q) functions of NiZr and CuZr are remarkably similar, while the S(Q) of the zirconium alloys exhibited a broader first peak than those of the titanium alloys. Also, the titanium-containing samples have their first peak at higher Q-values than the zirconium-containing samples (approximately 2.9 angstrom-1 vs. approximately 2.7 angstrom-1). Both the X-ray and neutron patterns indicate that there were still some crystalline phases present in the amorphous zirconium alloy samples. Since titanium has a negative scattering length for neutrons, the total neutron structure factors [S(Q)]n of the titanium alloys are dominated by the chemical short-range order (CSRO), and the measured S(Q) indicate preference for unlike nearest neighbors in amorphous NiTi and CuTi.