# High-Temperature Mechanochemical Synthesis of Nano-ZrO2 for Enhanced Densification and Fracture Toughness in B4C Ceramics

## TL;DR

A new method to synthesize nano-ZrO2 using high-temperature mechanochemistry improves the strength and toughness of B4C ceramics.

## Contribution

A novel high-temperature mechanochemical synthesis of nano-ZrO2 is introduced to enhance B4C ceramic properties.

## Key findings

- HTMT nano-ZrO2 reduces ZrO2 transition temperature to 500 °C and produces 9.12 nm particles.
- HTMT nano-ZrO2 improves B4C ceramic densification and reduces porosity and grain coarsening.
- 4 wt% HTMT nano-ZrO2 addition achieves high relative density (99.75%) and fracture toughness (4.74 MPa/m1/2).

## Abstract

In this investigation, a novel process for the synthesis of nano-ZrO2 powders based on high-temperature mechanochemical technology (HTMT) in a short process is proposed and HTMT nano-ZrO2 enhancement mechanism as an additive on the properties of B4C ceramics was systematically investigated. ZrO(OH)2 was used as a precursor, and ZrO2-B4C composites were prepared by optimizing the ball milling temperature and time in combination with the hot-press sintering technique. The results demonstrated that the high-temperature mechanical force causes the transition temperature of ZrO2 from monoclinic to tetragonal crystal system to be decreased to 500 °C. The ZrO2 treated by high-temperature ball milling at 600 °C/6 h exhibits lower microstress, higher crystallinity, and a particle size of only about 9.12 nm. HTMT nano-ZrO2 effectively controls the size of in situ generated ZrB2 particles in B4C ceramics, reduces interfacial porosity and grain coarsening, and promotes densification of B4C ceramics compared to commercially available nano-ZrO2. With the addition of 4 wt% HTMT nano-ZrO2, the composite showed optimal comprehensive properties: relative density of 99.75% (2.57 g/cm3), fracture toughness of 4.74 MPa/m1/2, flexural strength of 266.61 MPa, Vickers hardness of 31.14 GPa, and fracture mode with mixed mechanism of through-crystallization and along-crystallization.