• F Karimzadeh

      Articles written in Bulletin of Materials Science

    • Thermodynamic aspects of nanostructured Ti5Si3 formation during mechanical alloying and its characterization

      S Sabooni F Karimzadeh M H Abbasi

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      Mechanical alloying (MA) was used to produce Ti5Si3 intermetallic compound with nanocrystalline structure from elemental powders. The structural changes and characterization of powder particles during milling were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and microhardness measurements. MA resulted in gradual formation of disordered Ti5Si3 intermetallic compound with crystallite size of about 15 nm after 45 h of milling. Also a thermodynamic analysis of the process was carried out using Miedema model. The results showed that in the nominal composition of Ti5Si3 intermetallic phase (𝑋Si = 0.375), formation of an intermetallic compound has the lowest Gibbs free energy rather than solid solution or amorphous phases. So the MA product is the most stable phase in nominal composition of Ti5Si3. This intermetallic compound exhibits high microhardness value of about 1235 HV.

    • Nanoscale grain growth behaviour of CoAl intermetallic synthesized by mechanical alloying

      S N Hosseini M H Enayati F Karimzadeh

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      Grain growth behaviour of the nanocrystalline CoAl intermetallic compound synthesized by mechanical alloying has been studied by isothermal annealing at different temperatures and durations. X-ray diffraction method was employed to investigate structural evolutions during mechanical alloying and annealing processes. The disordered CoAl phase with the grain size of about 6 nm was formed via a gradual reaction during mechanical alloying. The results of isothermal annealing showed that the grain growth behaviour can be explained by the parabolic grain growth law. The grains were at nanometric scale after isothermal annealing up to 0.7 𝑇m. The grain growth exponent remained constant above 873 K indicating that grain growth mechanism does not change at high temperatures. The calculated activation energy indicated that the grain growth mechanism in the disordered CoAl phase at high temperatures was diffusing Co and Al atoms in two separate sublattices. Furthermore, an equation has been suggested to describe the grain growth kinetics of nanocrystalline CoAl under isothermal annealing at temperatures above 873 K (𝑇/𝑇m ≥ 0.5).

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