Study of hcp-fcc Allotropic Transformation on Heat-Treated Commercially Pure Titanium Alloy

Abstract

Titanium alloys can exhibit a wide variety of microstructures since they exhibit a wide range of phase transformations. Commercially pure grade 2 titanium alloys can be expected to have the presence of the α hexagonal compact (HCP) and β body-centered cubic (BCC) phases. However, in this research the formation of an unusual phase of face-centered cubic (FCC) structure is reported. The study of the FCC phase is carried out on samples thermally treated at 500°C, 800°C, 900°C, integrating different techniques as optical microscopy, scanning electron microscopy, orientation microscopy, X-ray diffraction and DTA differential thermal analysis. The development of a FCC phase with a non-homogeneous distribution towards the interior of the samples was detected, which seems to indicate that the phase requires surface deformation. Although the initial hypothesis indicates that this transformation may have probably been induced during the polishing process, this work analyzes the dependence between the degree of development of this phase and the thermal treatment of the material.