Rhenium, as a key element for enhancing the high-temperature strength, creep resistance, and microstructural stability of structural materials, possesses unique advantages in the field of high-temperature structural materials. In conventional titanium alloy development, rhenium has been primarily used as a stabilizer of the body-centered cubic β phase. Leveraging its large atomic size and slow diffusion kinetics, it effectively suppresses diffusion-controlled microstructural coarsening, thereby improving the high-temperature mechanical performance of the alloy. However, this traditional strengthening strategy relies heavily on the stability of the β phase and fails to fundamentally address the intrinsic performance bottleneck of the dominant hexagonal close-packed α phase in titanium alloys at elevated temperatures.

The core challenge currently facing this field is that the equilibrium solid solubility of rhenium in α-titanium is extremely low, and prolonged high-temperature exposure readily causes severe segregation or precipitation of rhenium, leading to a rapid failure of the long-term solid-solution strengthening effect. As a result, the α phase still maintains relatively fast atomic diffusion kinetics at high temperatures, exhibiting deficiencies such as insufficient high-temperature strength and susceptibility to microstructural instability, which greatly limit the service temperature ceiling of α-type titanium alloys. Therefore, how to overcome the thermodynamic solubility limit while simultaneously suppressing the diffusion of rhenium at high temperatures and achieving direct strengthening and stability control of the α phase has become a critical technical challenge that needs to be addressed in the design of a new generation of high-temperature titanium alloys.

To address the above issues, a team led by Zhejiang University and others conducted systematic research using ZEPTOOLS' in-situ TEM measurement system. By combining laser selective melting with heat treatment, the team successfully fabricated a single-phase α-TiRe alloy with a nanoscale modulated structure, and for the first time elucidated the high-temperature strengthening mechanism in which geometrically necessary misfit dislocation arrays stabilize the non-equilibrium microstructure by locking rhenium atom diffusion, achieving high-temperature strength and microstructural stability far exceeding those of conventional α-titanium alloys at 700°C.

Title:Dislocation-enabled rhenium locking stabilizes high-temperature spinodal α-Ti
Journal:Journal of Materials Science & Technology
URL:https://doi.org/10.1016/j.jmst.2026.07.020

To address the challenges of low solid solubility and high-temperature segregation propensity of rhenium in α-titanium alloys, the research team proposed a defect-mediated microstructural regulation strategy. By combining laser selective melting in additive manufacturing with subsequent refined heat treatment, they successfully fabricated a single-phase HCP-structured Ti-0.35Re alloy with a rhenium atomic fraction of 0.35%. Microstructural characterization revealed that the alloy contains a nanoscale spinodal decomposition structure, in which the lamellar rhenium-rich phase has a width of approximately 20 nm and maintains a fully coherent interface with the α-titanium matrix. Owing to the lattice misfit induced by spinodal decomposition, high-density geometrically necessary misfit dislocation arrays, composed primarily of -type dislocations, spontaneously form at the coherent interfaces and within the rhenium-rich phase, thereby constructing a unique composite microstructure of nanophase and dislocation networks within the single-phase α-titanium matrix.

To elucidate the microscopic mechanism of misfit dislocation arrays during deformation, the researchers conducted in-situ tensile loading experiments on the Ti-0.35Re alloy in displacement-controlled mode using ZEPTOOLS' in-situ tensile holder. The experiments recorded in real time the highly significant dynamic interaction between mobile dislocations and the misfit dislocation arrays. It was found that the misfit dislocation arrays at the interfaces act as strong pinning points, effectively hindering the rapid advancement of gliding dislocations, forcing them to change direction or reorient along the misfit array, thereby inducing dense dislocation tangles. This dislocation interaction, confirmed by in-situ TEM observation, demonstrates that the misfit dislocation network significantly enhances the alloy's ability to impede dislocation motion during deformation, providing direct microscopic mechanical evidence for the high-temperature strengthening of the alloy.

In terms of high-temperature thermal stability, the study revealed the core physical mechanism by which misfit dislocation arrays lock rhenium atom diffusion. Owing to the large atomic size of rhenium and its slow diffusion kinetics in α-titanium, the high-density misfit dislocation network can trap rhenium atoms enriched in the spinodal lamellae, significantly suppressing long-range diffusion and segregation coarsening of rhenium under high-temperature conditions. Transmission electron microscopy analysis showed that after high-temperature exposure at 600°C for approximately 25 minutes and at 700°C for approximately 23 minutes, the nanoscale spinodal structure and interfacial misfit dislocation arrays within the alloy remained intact, without obvious microstructural coarsening or phase decomposition, demonstrating exceptionally strong thermal microstructural stability and successfully overcoming the susceptibility to microstructural instability commonly observed in conventional α-titanium alloys at elevated temperatures.

Macroscopic mechanical property testing further confirmed the outstanding effectiveness of this dislocation-locking rhenium strategy. In high-temperature tensile tests at 700°C, the Ti-0.35Re alloy with the nanoscale modulated structure exhibited a yield strength as high as 191 MPa, far exceeding the 122 MPa of the solid-solution treated control alloy without the modulated structure. More critically, when the testing temperature was increased from 600°C to 700°C, the high-temperature strength retention rate of this alloy reached 68%, whereas that of the solid-solution treated alloy was only 30%. This research establishes a new mechanism for stabilizing non-equilibrium microstructures through misfit dislocation locking of solute atoms, demonstrating that rhenium can serve as an efficient high-temperature strengthening element for α-titanium. It provides an important theoretical basis and technical pathway for overcoming thermodynamic solubility limits and designing novel high-temperature titanium alloys that surpass traditional service temperature limits.

ZEPTOOLS, as a Chinese high-end precision instrument company, is a first-class supplier of in-situ electron microscopy characterization solutions. Its PicoFemto series of in-situ transmission electron microscopy characterization solutions have successively provided technical support for significant research results of domestic and international users. The following image shows the ZEPTOOLS in-situ TEM sample holder product used in this research: