Microscale mechanical properties of ultra-high-strength polysynthetic TiAl-Ti₃Al single crystals

The excellent mechanical properties of recently developed polysynthetic TiAl-Ti₃Al intermetallic single crystals lead to a high motivation to explore the micro-mechanical properties of their constitutional phases. However, the mechanical properties of the individual phases at the nanoscale are hard to obtain since the measurement requires a high lateral resolution and superior mechanical sensitivity. Here, using a method of scanning nanoindenter together with nanoDMA, we report the critical data of modulus maps and the nanoindentation hardness of their individual phases at the nanoscale. Furthermore, the yield strength and plasticity of the individual phases were obtained using an in situ nanoindentation on the focused ion beam machined nanopillars. The value of elastic modulus is measured to be about 140 and 180 GPa, respectively for α₂-Ti₃Al and γ-TiAl intermetallic phases, for samples with 0° lamellar orientation, which is higher than the value of about 120 and 160 GPa for the same phases in samples with 45° lamellar orientation. The relationship between the microscale and macroscale modulus can be described using the Voigt-Reuss approximation. More importantly, AFM results show that the plastic deformation is more uniform for the single crystals with 0° lamellar orientation, since they have more homogeneous microstructure and smaller difference in the hardness between the two phases. Our findings are useful to promote the applications and design of new TiAl-based single crystals as structural materials, from the perspective of the microstructure and micro-mechanical properties.