## 3 Results and Discussion
### Thermal Conductivity Results  
When the test temperature range varies between 25 and 300 \({}^{\circ}\)C, the effect of radiation heat transfer can be neglected. Moreover, considering heat loss, the Cowan+ impulse correction was adopted. Figure 6 displays the thermal conductivities of cleaned bare OFHC, Ti films, and Ti-Zr-V-Hf films with untreated OFHC and laser processed OFHC in the test temperature ranging from 25 to 300 \({}^{\circ}\)C. It can be seen that the thermal conductivities of all the samples decreased gradually with the increase of temperature. The thermal conductivities of the cleaned bare OFHC sample vary between 417.7 W m\({}^{-1}\) K\({}^{-1}\) and 382.3 W m\({}^{-1}\) K\({}^{-1}\) in the temperature range of 25-300 \({}^{\circ}\)C, which are consistent with reported values [27; 28; 29; 30; 31]. For the films deposited on the untreated OFHC substrate, the thermal conductivities of Ti films were 3.3%-10.2% higher than the Ti-Zr-V-Hf films at the same temperatures. In comparison, the thermal conductivities of Ti films on the laser processed OFHC were 6.3%-20.1%  
Figure 5: The secondary electron yield (SEY) of laser processed OFHC, Ti film, and Ti–Zr–V–Hf coated laser processed OFHC substrates. higher than the Ti-Zr-V-Hf films with the same substrates. Additionally, the thermal conductivity differences between Ti and Ti-Zr-V-Hf films increased gently with the increase of test temperature. When the substrates are the same, the thermal conductivities of Ti films are higher than the ones of Ti-Zr-V-Hf quaternary alloy films. The structural disorder degree of Ti-Zr-V-Hf films are higher than that of Ti film, which may contribute to the thermal conductivity difference [27; 32; 33; 34]. In addition to the film composition, the laser processing also influences the thermal conductivity but the roles are complicated. Laser processing treatment significantly reduces the thermal conductivity of the bare cleaned OFHC. However, in the presence of coatings, laser processing on the OFHC substrate becomes beneficial. Figure 6 shows that the thermal conductivities of Ti films with cleaned laser processed OFHC substrates are higher than the ones with cleaned OFHC substrates. In particular, when the test temperatures are 250 and 300 \({}^{\circ}\)C, respectively, the thermal conductivities of cleaned OFHC and Ti films with cleaned laser processed OFHC substrates are very close. Concurrently, the thermal conductivities of Ti films with cleaned laser processed OFHC substrates are higher than the ones with cleaned OFHC substrates. However, the thermal conductivities of Ti-Zr-V-Hf films with cleaned untreated OFHC and laser processed OFHC substrates are equivalent to a certain degree. Interface bonding plays a pivotal role in the thermal conductivities of Ti and quaternary alloy Ti-Zr-V-Hf films with cleaned OFHC substrates. The mechanism of the effect of interface bonding on thermal conductivity has been reported by other scholars [35]. Higher disorder degree results in low thermal conductivities for the quaternary alloy with respect to Ti film. The results confirm that cleaned laser processed OFHC substrates coated with Ti has a positive effect on the thermal properties compared with Ti film on cleaned OFHC substrates. It can be speculated that the interface bonding of Ti film with cleaned OFHC substrates is worse than the one with cleaned laser processed OFHC substrates. This can be attributed to the thermal conductivity increase of Ti film with cleaned laser processed OFHC substrates. Nevertheless, the disorder degree of Ti film is lower than the one of Ti-Zr-V-Hf film. The coupling effect of interface bonding and disorder degree results in the thermal conductivity difference for Ti and quaternary alloy Ti-Zr-V-Hf films with different kinds of OFHC substrates. In other words, the porous layer is formed on the surface of the substrate after laser processing, which can induce thermal conductivity reduction to some extent.