Microstructural development for optimum fracture toughness of Al₂O₃-3YSZ composites

ABSTRACT

Alumina-based ceramics are widely used for making wear-resistant components and machine parts due to their high hardness, strength, wear-resistance, and high chemical and thermal stability. However, low fracture toughness (K_IC ~ 3.0 MPa.m^1/2) inhibits alumina’s usage where high toughness is a pre-requisite (e.g. ceramic engines). In this work, yttria-stabilised zirconia (3YSZ) was added to alumina and a two-step sintering process was used to make a composite with enhanced mechanical properties. The key properties – hardness, fracture toughness, and percentage theoretical density (D_th) – could be related to microstructural features. It was revealed that higher numbers of elongated grains formed with increasing additions of 3YSZ. The maximum fracture toughness and hardness achieved were 5.51 MPa.m^1/2 and 10.96 GPa, respectively, for the Al₂O₃-30 wt% 3YSZ composite, believed mainly due to the high proportion of elongated grains. The best-performing sample had a density of 96.1% D_th and the average grain size was 0.35 µm. The thermal expansion coefficient was measured as 6.5 × 10⁻⁶ K⁻¹.

KEYWORDS:

• Alumina-3YSZ composite
• microstructure
• phase transition
• hardness
• fracture toughness

Acknowledgments

The authors are grateful to the Department of Glass and Ceramic Engineering and Department of Materials and Metallurgical Engineering of BUET for their technical support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Compliance with ethical standards

Funding: This study was funded by the Directorate of Advisory, Extension and Research Services (DAERS)-No. DAERS/CASR/R-01/2018/DR-2392(42), Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh.

Additional information

Funding

This work was supported by the Directorate of Advisory, Extension and Research Services [(DAERS)-No. DAERS/CASR/R-01/2018/DR-2392(42)], Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh.