Evolution of Face-Centered Cubic Ti Alloys Transformation by X-ray Diffraction Profile Analysis in Mechanical Alloying

Edgar Pio,Felipe Cerda,Claudio Aguilar,Carola Martínez,Ariosto Medina

doi:10.3390/met11111841

Abstract

Four titanium alloys (Ti-Ta, Ti-Ta-Sn, Ti-Ta-Mn, and Ti-Nb-Sn) were synthesized by mechanical alloying (MA) in a planetary mill in different times between 2 h and 100 h. The microstructure characterization was made by X-ray diffraction (XRD), in which the Rietveld method was applied to analyze the diffraction patterns. The study demonstrated that after short milling times between 2 h and 30 h, the fraction of hexagonal close-packed (hcp) phase decreases; at the same time, the formation of body-centered cubic (bcc) and face-centered cubic (fcc) Ti phases are promoted. Additionally, after 30 h of MA, the full transformation of hcp-Ti was observed, and the bcc-Ti to fcc-Ti phase transformation took place until 50 h. The results suggest that the addition of Ta and Sn promotes the fcc-Ti phase formation, obtaining 100% of this phase at 50 h onwards, whereas Nb and Mn show the opposite effect.

Highlights

Titanium and titanium alloys have been used commercially since the early 1950s due to their unique properties, such as high strength-to-weight ratio, high melting point, and excellent corrosion resistance in chloride-containing media [1,2,3,4]
A metastable phase with a face-centered cubic crystal structure has been reported by several authors in pure Ti and Ti-based alloys [16,17,18,19,20,21,22,23,24]
The X-ray diffraction (XRD) powder patterns of the alloys were recorded on a multipurpose powder diffractometer STOE STADI MP (STOE & Cie GmbH, Darmstadt, Germany) equipped in transmission geometry

Summary

Introduction

Titanium and titanium alloys have been used commercially since the early 1950s due to their unique properties, such as high strength-to-weight ratio, high melting point, and excellent corrosion resistance in chloride-containing media [1,2,3,4]. Chatterjee et al [17] reported the formation of nanocrystalline grains and partial transformation to a fcc Ti-phase after 10 h of milling pure Ti powder. Two common characteristics have been reported to obtain the γ-phase: (i) nanocrystalline grain size and (ii) high deformation This indicates that transformations of Ti could be induced by deformation during milling [24,28,29,30,31,32]. Chicardi et al [45] studied the synthesis of TiNbxMn by MA, reporting that the addition of Mn after 10 h of milling time promotes the stabilization of fcc Ti-phase. The Ti powder alloys were synthesized by mechanical alloying (MA) using a planetary ball mill in Yttrium-stabilized Zirconia media and characterized by X-ray diffraction pattern profile analysis

Synthesis of Ti Alloys

Microstructural Characterization

Determination of Dislocation Density from XRD

Findings

Conclusions