CrTa0.5Nb0.5O4: A solid solution strategy to enhance the mechanical and thermal properties of rutile structured ternaries

CrTaO 4 and CrNbO 4 , rutile structured ternary scales formed on refractory high-entropy alloys (RHEAs), protect the RHEAs from oxidation and thermal attack. However, the Vickers hardness (12.20/10.20 GPa for CrTaO 4 and CrNbO 4 , respectively) is lower than that of YSZ (14 GPa), making them prone to erosion. In addition, further reduction of thermal conductivity (1.31/1.09 W·m −1 ·K −1 for CrTaO 4 and CrNbO 4 , respectively) benefits to protect the substrate materials from thermal attack. As such, optimizing their properties is urgently needed. To enhance the mechanical properties and further reduce the thermal conductivity of rutile-type ternary oxides CrTaO 4 and CrNbO 4 , herein we designed a CrTa 0.5 Nb 0.5 O 4 solid solution based on the mechanism of solid solution strengthening, and systematically investigated its phase composition, microstructure, mechanical and thermal properties. The HAADF and ABF-STEM analyses confirmed the rutile-structure of CrTa 0.5 Nb 0.5 O 4 , while minor impurities of rutile-structured CrNbO 4 and CrO 2 were also identified. The elastic modulus, bulk modulus, and shear modulus of CrTa 0.5 Nb 0.5 O 4 are 201, 119, and 175 GPa, respectively. Notably, the mechanical properties of CrTa 0.5 Nb 0.5 O 4 have been significantly improved via solid solution strengthening, with the Vickers hardness of 13.01 ± 0.2 GPa, fracture toughness of 2.07 ± 0.017 MPa·m 1/2 , and flexural strength of 201 ± 12 MPa. The measured melting point of CrTa 0.5 Nb 0.5 O 4 is 2073±20 K, with an average thermal expansion coefficient of (5.91±0.52) × 10⁻ 6 K⁻ 1 . The room-temperature thermal conductivity of CrTa 0.5 Nb 0.5 O 4 is 1.07 W·m⁻ 1 ·K⁻ 1 , which decreases to 0.57 W·m⁻ 1 ·K⁻ 1 at 1473 K, being lower than most of the well-known thermal barrier coating materials. In terms of thermal expansion coefficient matching, CrTa 0.5 Nb 0.5 O 4 is a qualified thermal barrier material for refractory metals and their alloys and ultra-high temperature ceramics. Therefore, this study has not only successfully developed a thermal barrier coating material with excellent mechanical properties and low thermal conductivity, but also provided new ideas for the research and development of materials in high-temperature fields from the perspective of material design.