Fig. 1. Six samples after heat treatment and inlay

Fig. 2. Schematic diagram of the LIBS experimental setup for TC4 titanium alloy detection

Fig. 3. Timing diagram of laser-induced plasma radiation spectrum

Fig. 4. LIBS pulse laser ablation crater on the surface of the sample. (a) Macroscopic schematic diagram of ablation crater;(b) Microscopic schematic diagram of ablation crater

Fig. 5. Spectral line intensity of Al versus the hardness for 6 samples. (a) Al Ⅱ 281.619 nm; (b) Al Ⅰ 396.152 nm

Fig. 6. Spectral intensity ratio of Al Ⅱ 281.619 nm and Al Ⅰ 396.152 nm for 6 samples

Fig. 7. Spectral intensity ratio of Al Ⅱ 281.619 nm and Al Ⅰ 396.152 nm versus the hardness of TC4 samples

Fig. 8. Boltzmann plots of 6 TC4 titanium alloy samples with different hardness. (a) S1; (b) S2; (c) S3; (d) S4; (e) S5; (f) S6

Fig. 9. Plasma excitation temperatures versus the hardness of TC4 samples