Determination of α lamellae orientation in a β-Ti alloy using electron backscatter diffraction

Area of Science:

• Materials Science
• Metallurgy
• Crystallography

Background:

• Metastable beta-titanium alloys like Timetal LCB are crucial in aerospace and biomedical applications.
• Understanding the microstructure, specifically the orientation of alpha lamellae within the beta matrix, is key to predicting alloy properties.
• The crystallographic relationship between alpha and beta phases influences mechanical behavior and phase transformation kinetics.

Purpose of the Study:

• To determine the spatial orientation of alpha lamellae within a metastable beta-titanium (β-Ti) matrix.
• To precisely define the crystallographic orientation of the hexagonal close-packed (α) lattice within the α lamellae.
• To establish the crystallographic relationship between the α and β phases in aged Timetal LCB.

Main Methods:

• Utilized a combination of small-angle X-ray scattering (SAXS).
• Employed scanning electron microscopy (SEM) for microstructural imaging.
• Applied electron backscatter diffraction (EBSD) for crystallographic orientation analysis.

Main Results:

• Identified habit planes of α laths to be close to {111}_β.
• Correlated these habit planes to (1320)_α in the hexagonal α phase coordinate system.
• Determined the longest α lamella direction to be approximately along a 〈110〉_β direction parallel to the habit plane.
• Successfully indexed all main axes and faces of an α lath in both cubic β and hexagonal α coordinate systems.

Conclusions:

• The crystallographic orientation of α lamellae within the β-Ti matrix of Timetal LCB has been precisely determined.
• The findings provide a detailed understanding of the α/β phase relationship, crucial for alloy design and performance prediction.
• This work establishes a framework for indexing crystallographic features in complex titanium alloys.