Raman Spectroscopy of Laser-Micro-Annealing-Induced Structural Changes in Ti-6Al-4V

This short study presents the results of micro-Raman investigations performed on the alloy Ti-6Al-4V, which was additively manufactured via metal fused filament fabrication (MF3). Local laser micro-annealing was applied at different power intensities to distinct regions. The applied laser power density was varied in the range of ~0.05 kW/cm2 to ~5 MW/cm2. Laser-induced compositional changes in structures, approx. 1 µm in diameter, arranged in an array, are laterally limited. Simultaneously, the surrounding matrix maintains its initial pristine material properties down to ~500 nm in spacing between neighboring structures, reproducibly. The presented results confirmed that the material contains residues of the organic-based binder system and its decomposition products. Besides the characteristic Raman modes related to hydrocarbon compounds, TiC, and defect carbon phases were identified. Unexpectedly, micro-Raman mapping measurements performed on regions exposed to laser power densities above 2.5 MW/cm2 for up to 2 min revealed the complete suppression of hydrocarbon modes. Additionally, laser micro-annealing applied under identical operating conditions initiates “carbonization” processes in regions predominantly composed of residues from the organic-based binder used in material preparation. This short initialization study is a prerequisite and first building block for the development of suitable laser annealing technology which allows the modification and functional texturization of Ti-6Al-4V alloys down to the sub-micro scale. The correlation between modified materials’ structural and mechanical properties will be the aim of our future studies. This would allow the design and fabrication of sophisticated tools using MF3 technology for, e.g., surgery biocompatible implants with locally tuned, favorable mechanical properties.