Microstructural Strengthening and Plastic Degradation of Ti-6Al-4V Induced by Laser Ablation

Laser weapons play an important role in the modern high-tech war. And such laser weapon is based on the principle of thermal damage to 'burn' enemy equipment, such as missiles, drones, etc. To investigate the interaction mechanism between laser and common aerospace materials, the microstructure evolution and mechanical response of titanium alloys after laser ablation were studied in detail. The results indicate that in addition to the laser-induced failure zone (ablation area), a significantly large heat-affected zone exists, where the microstructure and mechanical characteristics change. Along the radial direction of the ablation area, the microstructure evolves from coarse lamellar microstructure to needle-like alpha/alpha ' with beta grain boundary, then to the bimodal microstructure of prior alpha and secondary alpha, and finally to the matrix that is mostly made of equiaxed alpha. Moreover, it is found that needle-like alpha, refinement grains and high oxygen content are the main reasons for the increase of microhardness. And the oxygen content above the acceptable level and severe segregation of solute elements may be the reasons that finally lead to the indentation cracks. The findings may offer ideas for the design of defensive Ti alloys, as well as the application in laser repair techniques.