Effect of interface energy anisotropy on thermal stability and transformation of lamellar Structures: II. Transformation of lamellae

Abstract

Thermodynamic regularities of the transformation of a lamellar shape into a spherical one is analyzed on the basis of the comparison of interface energies of spheres and disks. It is revealed that the motive force of spheroidization in two-phase systems with a high level of anisotropy occurs during high-temperature deformation due .to developing recrystallization processes. In systems with a low level of interface energy anisotropy the motive force considerably increases due to recrystallization. The causes of a specific behaviour of systems consisting of phases with different types of interatomic bonds are noted.

Influence of deformation on the Burgers orientation relationship between the α and β phases in Ti–5Al–5Mo–5V–1Cr–1Fe

“…These trends can be ascribed to the substantial inhomogeneity in the strain distribution associated with hot working of titanium alloys with a colony- microstructure [2]. 6 The effect of strain on the maximum and minimum values of  (Fig. 5a) was further elucidated in more-detailed distribution plots (Fig.…”

“…Spheroidization is associated with a series of microscopic processes consisting of the development of transverse low-angle boundaries within the  phase; the formation and growth of grooves at the  interphase boundary; fragmentation of the lamellar platelets by the grooves; and final spheroidization and coarsening of the resulting small-aspect ratio  particles by diffusional processes [e.g., [3][4][5]. As shown in [6,7], the nature of interphase / boundaries can have a major influence on the kinetics of spheroidization.…”

Microstructure evolution during warm working of Ti–5Al–5Mo–5V–1Cr–1Fe at 600 and 800 °C

“…The mechanisms and kinetics of the spheroidization of lamellar microstructures in a/b titanium alloys such as Ti-6Al-4V have been investigated over a wide range of hot-and warm-working temperatures [5][6][7][8]. At high temperatures, spheroidization is often associated with (i) the generation of transverse boundaries within alpha lamellae, (ii) the subsequent formation of grooves associated with the instability of 901 dihedral angles between interphase a/b boundaries and intraphase a/a boundaries, and (iii) complete lamellar fragmentation by deepening of the grooves from both sides of the a lamellae.…”

“…Lamella thickness, deformation temperature, and the nature of the intragranular and a/b interfaces (e.g., boundary energy) are the main factors influencing the mechanism and kinetics of spheroidization [8,10,11]. Hence, the kinetics of recovery, recrystallization, shear band formation, etc.…”

“…within a lamellae strongly affect fragmentation [6]. In addition, the evolution of (semi)coherent a/b interphase boundaries into noncoherent ones during deformation [11] may enhance diffusion along the interfaces [8,12] but make slip transfer more difficult. The mechanisms and kinetics of deformation and spheroidization of lamellar microstructures in titanium alloys with large amounts of the b-stabilizing elements (and hence b phase at a given processing temperature) have been studied to a lesser degree than for Ti-6Al-4V.…”