Feasibility of CaZr4(PO4)6 as Radome TBC Based on Thermophysical and Thermal Cycle Performance Research

This paper investigates the feasibility of CaZr4(PO4)6 as a novel thermal barrier coating for SiO2f/SiO2, serving as a radome at 1200 °C. Initially, CaZr4(PO4)6 powder undergoes TG-DSC testing across a temperature range from room temperature to 1200 °C, demonstrating excellent phase stability within this range. Subsequently, the coating’s properties and the thermal cycling performance are examined. The results indicate that the thermal conductivity of CaZr4(PO4)6 falls within the range of 1.05 to 1.02 W·m−1·K−1 (RT ~ 1200 °C), with thermal expansion coefficients of the coating ranging from 2.07 to 5.55 × 10−6 K−1. Moreover, the thermal cycling lifetime of the CaZr4(PO4)6 coating is evaluated by performing 100 cycles (50 h) at 1200 °C. Mechanical properties are assessed through Vickers and Knoop hardness tests, revealing a fracture toughness of 1.4 Mpa·m1/2. The primary cause of coating failure and peeling is the excessive internal stress between the coating and the expansion of transverse cracks. Fracture toughness serves as a key performance indicator reflecting the material’s resistance to unstable crack expansion, so the failure of the coating is attributed to the limited fracture toughness and the thermal mismatch stress between the coating and the substrate. Based on the aforementioned research findings, CaZr4(PO4)6 might be the potential coating for SiO2f/SiO2 systems.