Effect of pre-synthesis LaNbO4 phase addition on the thermal shock resistance of Y2O3/LaNbO4 composite materials

Yttrium oxide material exhibits excellent vacuum and high-temperature chemical stability, making it an ideal first-choice refractory material for superalloy smelting. However, its poor fracture toughness and low thermal shock stability seriously limit its service life. The ferroelastic toughening phase LaNbO 4 provides excellent fracture toughness due to the ferroelastic domain switching toughening effect. This study focused on yttrium oxide materials, utilizing Y 2 O 3 , La 2 O 3 , and Nb 2 O 5 fine powders as the main raw materials. By incorporating ferroelastic functional unit characteristics, a pre-synthesis LaNbO 4 phase with good intrinsic fracture toughness was introduced into the Y 2 O 3 matrix. The effects of different LaNbO 4 contents on the phase composition, microstructure, mechanical properties, and thermal shock resistance of Y 2 O 3 /LaNbO 4 composite materials were subsequently investigated. The following results were obtained: 1) The optimal pre-synthesis temperature of LaNbO 4 was 1200 °C. At this temperature, LaNbO 4 powder with a fine grain and uniform grain size could be synthesized. 2) The Y 2 O 3 and LaNbO 4 phase resulted in mutual solid solution formation, leading to a change in grain size and mechanical strength of the Y 2 O 3 /LaNbO 4 composite material. 3) The addition of an appropriate amount of LaNbO 4 resulted in the formation of a structure filled with LaNbO 4 grains between the grain boundaries of Y 2 O 3 , effectively improving the fracture toughness and thermal shock stability of the materials. 4) The hardness and strength of LaNbO 4 were lower than the Y 2 O 3 phase, making the selection of LaNbO 4 phase addition to Y 2 O 3 crucial. The excessive addition of the LaNbO 4 phase caused the LaNbO 4 phase in the material to dominate. The hardness and strength of the Y 2 O 3 /LaNbO 4 composite materials were inferior to those of the Y 2 O 3 material, however, the fracture toughness and thermal shock stability improved due to the ferroelastic toughening effect. Therefore, an optimal amount of LaNbO 4 phase should be added to balance the fracture toughness and thermal shock stability of Y 2 O 3 /LaNbO 4 composite materials, while maintaining the hardness and strength of the Y 2 O 3 phase.