# Nanosecond Laser Ablation of Ti-6 Al-4V under Di erent Temperature
## 2 Experimental Materials and Methods  
The materials used in this study were Ti-6 Al-4V. All samples were selected from the same base metal. The size of the samples were all 100 mm \(\times\) 10 mm \(\times\) 2 mm. The samples were carefully polished before ablation. Its chemical element composition is shown in Table 1.  
In order to obtain the different situations of ablation craters, this study was divided into two groups of experiments:  
Experiment A: experiment of low pulsed laser fluence ablation at different temperature. The experiment was divided into 8 groups at different substrate temperatures of 50 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 250 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 350 \({}^{\circ}\)C and 400 \({}^{\circ}\)C, each group took 1 Ti-6 Al-4V slice to performed irradiation of 50 pulses.  
Experiment B: Experiment of high pulsed laser fluence ablation at different temperature. The experiment was divided into 8 groups at different substrate temperatures of 50 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 250 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 350 \({}^{\circ}\)C and 400 \({}^{\circ}\)C. Each group took 6 Ti-6 Al-4V samples and performed irradiation of 2\({}^{\text{n}}\) (n = 0, 1, 2, 3, 4, 5) pulses on samples separately.  
The nanosecond laser used for the ablation experiment was the Q-switch neodymium: yttrium-aluminum-garnet laser. The laser parameters of each experiment is shown in Table 2. The laser pulses were applied on the sample surface after focusing. Different laser energies and pulse numbers were obtained by changing the parameters of the laser equipment. A heater was used to heat the Ti-6 Al-4V slice, sample (Ti-6 Al-4V slice) and heater were placed on a mobile platform, which allowed the user to adjust the position of the sample. The schematic diagram of the experimental device is shown in Figure 1. We obtained the required spot size by focusing on the upper surface of the target. However, limited by focusing accuracy, the focus was actually below the upper surface.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Element** & **Fe** & **Al** & **V** & **H** & **C** & **O** & **N** & **Ti** \\ \hline Content/\% & \(\leq\)0.30 & 5.5–6.8 & 3.5–4.5 & \(\leq\)0.015 & \(\leq\)0.1 & \(\leq\)0.20 & \(\leq\)0.05 & remainder \\ \hline \end{tabular}
\end{table}
Table 1: Chemical composition of Ti–6 Al–4V.  
We estimated the spot diameter after focusing by measuring the diameter of the splash area produced by a single pulse, as shown in Figure 2. The splashing area diameter of two samples was measured, and the average value was taken as the spot diameter after focusing.  
After ablation, samples were fully cooled, the optical microscope image and data of ablation craters were obtained by a digital microscope HIROX KH-8700, and the scanning electron microscope images were obtained by a field emission scanning electron microscope (FESEM) HITACHI SU5000.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Experiments** & **A** & **B** \\ \hline Laser type & Continuum Surelite I-10 \\ Wavelength (nm) & 532 \\ Repetition rate (Hz) & 10 \\ Pulse width (ns) & 4–6 \\ Beam diameter (unfocused) (mm) & 6 \\ Spot diameter (focused) (\(\upmu\)m) & 133.516 \\ \hline Laser energy (mJ) & 20 & 100 \\ Laser fluence (focused) (\(\upmu\)J/\(\upmu\)m\({}^{2}\)) & 0.1429 & 0.7143 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Laser parameters of experiment.  
Figure 1: Schematic diagram of the ablation experiment.  
Figure 2: Diameter of the splash area were used to estimate the diameter of laser spot.