Mechanisms of globularization of Ti-6Al-4V during static heat treatment

Abstract

The mechanisms controlling static globularization of Ti-6Al-4V after deformation and annealing at 900 ЊC and 955 ЊC were established. Microstructural observations suggested that the process of globularization can be divided into two stages. The first includes microstructural changes during deformation and the initial stages of static heat treatment; the second occurs during prolonged static annealing. The initial stage consists of segmentation of the lamellae via boundary splitting, whereas microstructural coarsening characterizes the latter stage. Thus, the process of static globularization is only moderately dependent on the formation and evolution of dislocation substructure; the additional driving force is provided by the reduction in interface energy. The duration of the initial stage of static globularization was calculated by estimating the time required for the completion of the boundarysplitting process. The calculations were in excellent agreement with microstructural observations and showed that the duration of the initial stage at 900 ЊC and 955 ЊC lasted approximately 10 hours and 1 hour, respectively.

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

“…in which d a is the thickness of the a lamella, and m g represents the average slope at the root of the triple point [27]. The coefficient A is given by the equation [5]:…”

“…7d, e) also suggest that minimal termination migration occurred. Such observations can be ascribed to the low temperatures and typical findings that termination migration to complete spheroidization typically requires an order of magnitude more time than platelet fragmentation [27].…”

In situ observation of texture and microstructure evolution during rolling and globularization of Ti–6Al–4V

“…The possible mechanisms by which lamellar microstructures globularise and coarsen into a globular α p morphology has been studied by various investigators [3][4][5][6][7][8]. Initial work by Weiss et al identified two different boundary splitting mechanisms by which lamellar microstructures globularise.…”

Evolution of Microstructure and Residual Stress in Hot Rolled Ti-6Al-4V Plates Subjected to Different Heat Treatment Conditions

“…The break-up of lamellae by globularization as observed in the HT1 and HT2 conditions was characteristic of recrystallization annealing high in the + phase field (>900 o C) [5]. An increased fraction and size of globular in the HT2 condition may be due to a further annealing cycle; or increased temperature or duration than that experienced in the HT1 condition, resulting in the progression of globularization kinetics [5].…”

“…An increased fraction and size of globular in the HT2 condition may be due to a further annealing cycle; or increased temperature or duration than that experienced in the HT1 condition, resulting in the progression of globularization kinetics [5]. Globularization in Ti-6Al-4V has been associated with stress relaxation; due to rearrangement of dislocations which can annihilate as they move through the lattice, reducing dislocation density and therefore internal strain [6].…”