Microstructure and Properties of Al₂O₃-Y₃Al₅O₁₂ Reactive Sintered Ceramic Composites with Multilayer Compositional Gradient: an Initial Investigation

In this work, mixtures of ceramic powders containing Al₂O₃ with different amounts of Y₂O₃ (1%, 3%, 5% and 10wt.%) along their cross-section were fabricated to obtain multilayer composites based on Al₂O₃ with different levels of Y₃Al₅O₁₂ (YAG) as reinforcement. Monolithic cylindrical multilayer Al₂O₃ blocks were compacted and subsequentially, sintered at 1610°C for 4h. Phase stability, microstructural aspects, and physical and mechanical properties of the specimens were acquired by relative density, X-ray diffraction, scanning electron microscopy, Vickers hardness, fracture toughness, Young’s modulus and biaxial flexural strength measurements. The results indicated that monolithic alumina specimens exhibited relative density of 98%, with average hardness of 1203 ±83 HV, fracture toughness of 2.1 ±0.8 MPa.m^1/2 and flexural strength of 187 ±64 MPa. Progressive incorporation of Y₂O₃ into the chemical composition of the specimens led to formation of the YAG phase by solid state reaction during sintering, which reduced hardness and increased densification, fracture toughness and flexural strength, with average values of HV=1023 ±28 HV, K_IC=3.5 ±0.3 MPa.m^1/2, σ_f=273 ±58 MPa and 14% Y₃Al₅O₁₂ for the specimens with 10wt.% Y₂O₃. This improvement is probably associated with toughness mechanisms, such as crack deflection and residual thermal stresses between the phases present in the composites.

Keywords:
Multilayer composites; Al₂O₃-Y₃Al₅O₁₂ ceramic composite; gradient composition; mechanical properties