X-ray diffraction study of the amorphization process by mechanical alloying of the NiTi system
1988; Elsevier BV; Volume: 97; Linguagem: Inglês
10.1016/0025-5416(88)90009-2
ISSN1873-4928
AutoresG. Cocco, Stefano Enzo, L. Schiffini, L. Battezzati,
Tópico(s)Shape Memory Alloy Transformations
ResumoX-ray Fourier methods were used to follow fragmentation phenomena and structural defects during mechanical alloying processes in the NiTi system. Furthermore, a methodological X-ray diffraction approach was developed to study the kinetics of the process up to complete amorphization of the powders. Results show that the effective crystallite size and defect concentration of the unreacted powders achieve asymptotic values after mechanical alloying for about 5 h, whereas the amorphization process is accomplished after 30 h. The limiting value of the effective sizes, calculated after correction for the strain contribution, is around 30 nm, which is one order of magnitude larger than the values reported in these materials from a line-broadening analysis using the Scherrer equation. As for the defect concentration, elemental titanium and nickel powders milled separately show approximately the same strain content as the NiTi mixture treated under the same experimental conditions. However, the pre-induced disorder does not speed up the solid state reaction; in fact, when the single elements milled separately are reacted, the amorphization process is also completed in 30 h.
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