Effect of cryomilling on matrix/reinforcement interfaces and properties of Al-TiB2 composites

Highlights: • Microstructures of Al-TiB₂ composites were investigated with respect to their TiB₂ content. • Cryomilling had positive effects on the uniform distribution of TiB₂ particles. • No formation of intermetallic phases, such as Al₃Ti, was observed at the interfaces. • 10-min cryomilling before sintering led to elastic moduli of 283–433.7 GPa (TiB₂). • The absence of interfacial reactions improved the mechanical properties. The present study reports the effects of cryomilling on the microstructural and mechanical properties of pressurelessly sintered Al-xTiB₂ (x = 5, 10, or 15 wt%) composites. Composite powders milled under cryogenic conditions in the presence of liquid nitrogen were compacted in a hydraulic press, and the compacts were pressurelessly sintered at 650 °C for 5 h under Ar/H₂ gas. The effects of cryomilling time (10 or 20 min) and TiB₂ content (5, 10, or 15 wt%) on the microstructures, densities, and mechanical properties (wear characteristics, hardness, elastic modulus, indentation response) of the sintered products were investigated. Because the milling process was under cryogenic conditions, the formation of intermetallic phases between the matrix and reinforcement particles, such as Al₃Ti, was not observed at the interfaces of the sintered Al-TiB₂ composites, even when 15 wt% TiB₂ was used. Cryomilling for 10 min followed by pressureless sintering of Al matrix composites reinforced with 5–15 wt% TiB₂ particles resulted in bulk samples with relative densities of 97.38–98.43%, hardness values of 0.75–1.35 GPa, wear volume losses of 0.276–1.265 mm³, and elastic moduli of 283–433.7 GPa.