Isokinetic Analysis of Fe41Co7Cr15Mo14Y2C15B6 Bulk Metallic Glass: Effect of Minor Copper Addition

In the present study, (Fe41Co7Cr15Mo14Y2C15B6)100−xCux (x = 0, 0.25 and 0.5 at.%) amorphous alloys were prepared by copper-mold casting. To clarify the effect of the minor addition of copper on the mechanism of nucleation and growth during the crystallization process, an isokinetic analysis was performed. The activation energies (E) of the various crystallization stages were calculated by using theoretical models including Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Augis–Bennett and Gao–Wang methods. In addition, Augis–Bennett, Gao–Wang and Matusita methods were used to investigate the nucleation and growth mechanisms and to determine other kinetic parameters including Avrami exponent (n), the rate constant (Kp) and dimensionality of growth (m). The obtained results revealed that the activation energy—as well as thermal stability—was changed with minor addition of copper. In addition, the obtained Avrami exponent values were confirmed by Johnson–Mehl–Avrami–Kolmogorov (JMAK) method. The research findings demonstrated that the value of Avrami exponent is changed with minor addition of copper, so that the Avrami exponents of all crystallization stages, except the second peak for copper-free amorphous alloy, were equal to integer values ranging from two to four, indicating that the growth mechanisms were controlled by interface. Moreover, the kinetic parameters of n and b for all peaks were increased by an increase in crystallization temperature, which can be attributed to the increase in the nucleation rate.

Real-Time Studies of The Electrocrystallization of Nanoscale Ceramic Superlattices

ABSTRACTElectrodeposition is unique among thin film deposition techniques, since the current following a potential step from open circuit to a given overpotential (i.e., driving force) provides a real-time, in situ probe of the deposition process. We have used current-time transients to determine the kinetics and dimensionality of growth, and to calculatethe composition profiles of electrodeposited superlattices in the Pb-TI-O system. The transients are indicative of 2D growth, and the height of the 2D monolayer depends on the orientation of the film. A [100] oriented film has a step height of 0.13 nm and a [210] oriented film has a step height of 0.18 nm. These heights correspond to the (400) and (220) d-spacings, respectively. Using a Cottrell analysis, we were able to both calculate and tailor the composition profile in these superlattices. Superlattices grown by pulsing between 70 and 150 mV have square profiles, while those grown by pulsing between 70 and 230 mV have graded profiles.

Crystallization Kinetics Of Fe80-yVyB12Si8 Amorphous Ribbons

ABSTRACTThe effects of vanadium in the crystallization kinetics amorphous ribbons Fe80-yVyB12Si8 (0.5 < y < 15) has been investigated by Differential Scanning Calorimetry, by using the Avrami, Kolmogorov-Johnson-Mehl-Avrami, and Calka and Radlinski equations. The addition of vanadium to Fe-B-Si alloys leads to an enhancement of stability against crystallization, as shown by an increase in the effective activation energy for crystallization (Eeff = 3.6eV) and an increase in the temperature for the first crystallization peak, as a function of vanadium content (from 780 to 855K). Results also show that the crystallization Mechanism, nucleation rate and dimensionality of growth are constant throughout the crystallization process in the composition range investigated.