Assessing the potential of hypoeutectic Ti–Co alloys for semisolid processing

Hypoeutectic alloys are widely considered for semisolid processing. This study investigates hypoeutectic Ti–Co alloys for thixoforming, focusing on phase formation, melting behavior, semisolid microstructure, deformation behavior, and mechanical properties. Arc-melted Ti-Co ingots (Co contents: 17.5, 18.5, 19.5, and 20.5 wt%) were homogenized, hot-forged, and isothermally treated in the semisolid state at 1060 °C for up to 600 s. Characterization techniques included differential scanning calorimetry (DSC), scanning electron microscopy, high-temperature laser-scanning confocal microscopy (HT-LSCM), X-ray diffraction, semisolid compression tests, hardness testing, and room temperature compression tests. DSC results indicated that oxygen affects the eutectic transformation, extending the solidification interval. In-situ HT-LSCM experiments confirmed that eutectic melting occurs over a temperature range. Semisolid microstructures improved with higher Co content and longer isothermal treatments, while compression results aligned with typical semisolid alloy behavior. Both macroscopic and microscopic analyses showed enhanced deformation homogeneity and reduced defects with increased Co content. Thixoformed Ti-Co alloys exhibited high hardness and compressive strength, achieving approximately 1.5 GPa in yield strength. However, higher Co content reduced plasticity, attributed to the increased volume fraction of the Ti₂Co intermetallic phase.