*2.5. Thermal Fatigue Test*

Thermal fatigue tests were carried out by using a self-made thermal fatigue testing machine. Samples were heated in a high-temperature induction resistance furnace and cooled with tap water at room temperature. The heat cycle testing machine scheme is shown in Figure 6. Figure 7 illustrates the average surface-temperature variety of the test sample during one thermal cycle. Test samples were heated from room temperature to 700 ◦C in 160 s and then cooled to 24 ◦C in 5 s in one cycle. During thermal test, no samples had any externally applied loads. After tests, samples were taken out, and changes in the crack widths were measured, and the number of cold and hot cycles experienced by each sample was recorded. In this part, the thermal fatigue test was performed five times, and the average values are reported.

**Figure 6.** Sketch of the thermal-cycle testing rig.

**Figure 7.** The actual temperature profile of one thermal cycle (Point A and D—25 ◦C; B and C—700 ◦C).
