Significantly enhanced superplasticity of TiBw/near-α Ti composite: Microstructure tailoring and deformation mechanisms

Abstract

Titanium matrix composites(TMCs) have shown great potential for weight reduction in aerospace applications. However, hard ceramic reinforcements make the superplastic forming of TMCs hard to be achieved. In the present work, the microstructure of TiBw/near-α Ti composite was manipulated to achieve better deformability. Two different preprocessing routes were designed to obtain composites of equiaxed microstructure with the grain size of ∼3 μm, and bimodal microstructure with the grain size of ∼8 μm. Hot tensile test was carried out for the fabricated composites at 700 °C–800 °C and strain rates of 0.003 s−1 – 0.0003 s−1. The results showed that the deformability of the TiBw/near-α Ti composites was improved significantly, with a maximum elongation of 348% for the composite with equiaxed microstructure, and 161% for the composite with bimodal microstructure. The deformation was determined to be dominated by dislocation movement under temperatures below 800 °C and grain boundary sliding (GBS) dominated at 800 °C. α/β lath in bimodal microstructure was observed to hinder GBS while prompting dynamic recrystallization (DRX), which was consistence with the higher activation energy of the composite with bimodal microstructure (391 kJ/mol) compared to that of the composite with equiaxed microstructure (310 kJ/mol). Compared to reports in literatures, the deformation temperature of composites prepared in the present work was 50 °C lower than that fabricated by other methods, attributed to the tailored fine microstructure.