Effect of β grain growth on variant selection and texture memory effect during α → β → α phase transformation in Ti-6 Al-4 v

G. C. Obasi*, S. Birosca, J. Quinta Da Fonseca, M. Preuss

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

In the present study, the texture evolution and the role of β grain growth on variant selection during β → α phase transformation have been investigated in Ti-6 Al-4 V with and without 0.4 wt.% yttrium addition. The aim of adding yttrium was to control β grain growth above the β transus by pinning grain boundaries with yttria. Both materials were first thermomechanically processed to generate similar starting microstructures and crystallographic textures. Subsequently, both materials were solution-heat-treated above the β transus followed by slow cooling to promote growth of the α lath structure from grain boundary α. Additional interrupted slow cooling experiments were carried out to identify the α lamellae that nucleate first from β grain boundaries. Detailed electron backscatter diffraction analysis was carried out and it was found that the β heat treatment did not generate new texture components although the intensities of the individual components changed dramatically depending on the alloy/β grain size. Variant selection was assessed by comparing measured α texture components with predicted α texture components based on the high-temperature β texture assuming equal variant selection. It was found that with increasing β grain size variant selection intensified favouring the {1, Φ, 2} {90°, 30°, 0°} texture component. Interrupted cooling experiments revealed that α nucleates first on β grain boundaries that are formed by two β grains having a common (1 1 0) normal and that these α lamellae display almost exclusively a {1, Φ, 2} {90°, 30°, 0°} orientation. Consequently, the dominance of this variant with increasing β grain size can be related to the relative free growth of this particular α texture component into an "empty" β grain.

Original languageEnglish
Pages (from-to)1048-1058
Number of pages11
JournalActa Materialia
Volume60
Issue number3
Early online date15 Dec 2011
DOIs
Publication statusPublished - 1 Feb 2012

Keywords

  • Grain growth
  • Texture evolution
  • Texture memory
  • Ti-6 Al-4 V
  • Variant selection

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