Precipitation and phase evolution in a Cu-modified near-α titanium alloy designed for additive manufacturing

Developing lightweight high-temperature materials with excellent oxidation and creep resistance is crucial for improving efficiency in next-generation aerospace and energy systems. Near-α Ti alloys offer a promising balance of high specific strength, thermal stability, as well as oxidation resistance for such applications. However, exploiting their full potential, especially with additive manufacturing (AM), requires a deep understanding of their microstructural evolution under complex thermal conditions including phase transformations and precipitation pathways. Among various alloying strategies, Cu and Si additions show potential to promote grain refinement and enhance mechanical properties in Ti alloys processed by AM. However, the associated precipitation pathways, particularly those of Cu-rich intermetallics, remain largely unexplored in multicomponent near-α Ti systems. This study investigates phase transformations and precipitation behavior in a novel Cu- and Si-containing near-α Ti alloy using in situ high-energy X-ray diffraction (HEXRD) and small-angle X-ray scattering (SAXS), supported by transmission electron microscopy (TEM) and atom probe tomography (APT). Two intermetallic phases, Ti2Cu and S2-type (Ti,Zr)6Si3 silicides, are identified during continuous heating, each exhibiting distinct precipitation kinetics and thermal stability. SAXS reveals Ti2Cu precipitation already at ∼460 °C, indicating its potential formation at typical service temperatures (up to ∼600 °C). Quench rate experiments show that Ti2Cu precipitation can be suppressed at cooling rates above 50 °C/s, while forming between 620 and 500 °C at lower rates. These findings enable the design of heat treatments tailored for controlled precipitation and provide a foundation for future alloy development, contributing to improved efficiency and reliability of high-temperature components.