*2.4. Thermal Fatigue Test*

The equipment used in the thermal fatigue test was a self-made self-restrained thermal fatigue test machine, as shown in Figure 5. The heating temperature was 700 ◦C, and the cooling medium was running tap water. The heating time was 160 s, and the cooling time was 20 s. The melted sample and the untreated sample were placed in the thermal fatigue test machine for the thermal fatigue test. The samples were removed after the test, the number of cold and hot cycles was recorded, and finally the length and number of cracks were measured.

**Figure 5.** Shape and test process of the thermal fatigue testing machine.
