High Resolution EBSD Map of Additively Manufactured (AM) Ti-Alloys

Thanks to their excellent combination of strength, low weight and corrosion resistance, Ti alloys are widely used in critical applications such as aerospace and biomedical implants. Body Centered Cubic (BCC) Ti-beta alloys for instance, have a good hardenability, weldability and room temperature high yield strength. Yet, their high temperature strength is poor.¹ Thus, the presence of a second phase in the Ti-beta structure is essential to improve the material mechanical properties and to achieve a balancing of the desired mechanical behavior.​

Recently, Face Centered Cubic (FCC) Ti phase has been engineered via additive manufacturing in a Ti-6Al-4V alloy.² The formation of the FCC phase is facilitated by the combined effect of thermal gradients, deformation induced by the martensitic transformation, and local oxygen enrichment. The presence of the FCC Ti phase generates a higher ultimate strength of the alloy than the presence of Hcp Ti-alpha. No loss in the total tensile ductility was reported,² instead, the authors confirmed that the strength and ductility of the FCC-bearing materials (with ∼6 vol%) is strongly enhanced. Such structures were so far, only analyzed in transmission mode due to their fine sizes.​

In this example, a bulk additively manufactured Ti-beta alloy sample containing secondary FCC Ti phase is analyzed with the eWARP EBSD detector. Unprecedented high spatial resolution EBSD map is performed at 10 kV and 12 nA beam current, with a 30 nm pixel size. A small pixel size is essential for accurately resolving the ultrafine FCC Ti grains, allowing for precise characterization of their size, shape, and orientation distribution. Acquired and indexed at 4.988 frames per second, a 2.68 Mpixel map is indexed at >90% hit rate with 85,7% of BCC Ti-beta phase and 4,56% of FCC Ti phase fractions (Figure 1).

Grain statistics (Figure 2) show the fine FCC Ti structure, with an average size of 300 nm for the 1,278 analyzed grains. The martensitic Ti-beta matrix contains 3,608 grains, averaging 3.4 µm in size. Figure 1 illustrates very thin, film-shaped FCC grains, measuring 60 to 90 nm in width (2 to 3 pixels).

[1] Beta Titanium Alloys, Reference Module in Materials Science and Materials Engineering, 2017​

[2] H. Wang et al. Materials Today, Volume 61, 2022, Pages 11-21, ISSN 1369-7021