Papers by Keyword: Avrami Kinetics

Abstract: The flow curves determined on a series of Ni-Nb alloys are analysed. Six alloys containing Ni–0.01, 0.1, 1, 2, 5 and 10 wt. % Nb with pure Ni were tested in torsion at various strain rates within the hot forging temperature range. Under these conditions, large strains were attained, which permitted steady state flow to take place. The double-differentiation method is employed to define the critical strain for the initiation of DRX, leading to the evaluation of the strain hardening and dynamic recovery parameters. The relations obtained are compared to ones determined earlier using a least squares approach. It is shown that the two sets of relations do not differ appreciably. These results are employed to predict the Avrami kinetics of a range of Ni-Nb alloys strained at different temperatures and strain rates. The Avrami time exponents all fall in the range 1.0 to 5.0. The dependence of the time of half-softening, t₅₀, on Nb content, strain rate and temperature is also derived under the same conditions.

Abstract: The dynamic recrystallization of commercially pure titanium was investigated by compression tests on Gleeble-1500D thermal simulation test machine at temperature of 700950 °C and strain rate of 0. 015 s¹. The total compression deformation is 0.7(true strain). The kinetics of dynamic recrystallization of commercially pure titanium at 950 °C was modeled by Avrami equation. The results show that the dynamic recovery and recrystallization obviously occur during compression. The flow stress increases to a peak value and gradually decreases to a steady state. The flow stress is decreased with the increase of deformation temperature and it is increased with the increase of strain rate. The Avrami kinetics model of dynamic recrystallization of commercially pure titanium at 950 °C is obtained .

Abstract: A 0.02%C plain carbon and a 0.22%C TRIP steel were tested in compression in the temperature range 900°C to 1150°C and strain rate range 0.05s^-1 to 1s^-1. Thirty-two experimental flow curves were obtained in this way. The critical conditions for the initiation of dynamic recrystallization were determined by the double differentiation method. Using a dislocation density model to describe the austenite flow stress, the work hardening parameters r and h were derived and are used to model the flow curve in the absence of dynamic recrystallization. The latter was employed to calculate the fractional softening attributable to dynamic recrystallization. The kinetics of dynamic recrystallization are then described using Avrami kinetics. Finally, the dependences of the Avrami and work hardening parameters on Z, the Zener-Hollomon parameter, are used to model compression flow curves at strain rates an order of magnitude greater than the ones employed in the tests.