Heat treatment alone refines grain structure in tungsten and titanium alloys

Researchers at the University of Birmingham have identified a way for metals to refine their own internal structure during heat treatment, an approach that could help engineers develop stronger and more reliable materials for future fusion reactors and next-generation aerospace components.

The mechanism, named Precipitation Induced Recrystallisation (PIX), was identified with partners at the UK Atomic Energy Authority (UKAEA), TU Bergakademie Freiberg in Germany, and City University of Hong Kong. It allows a metal to produce a finer grain structure through heat treatment only, without the conventional mechanical processing normally needed.

The work is reported in two complementary studies, one in Communications Materials and one in Scripta Materialia. Together they demonstrate PIX in a titanium-iron-molybdenum alloy relevant to aerospace applications and in a tungsten-chromium alloy relevant to fusion energy systems.

In both materials the team found that tiny regions with different but symmetrically related atomic structures form during heat treatment. The mismatch that develops between those regions produces internal strain strong enough to create new, smaller grains inside the metal, with no prior rolling, forging or other mechanical deformation.

Project leader Sandy Knowles, Professor in Nuclear Materials at the University of Birmingham, said the finding challenges the conventional understanding that grain refinement typically requires extensive thermomechanical processing, and that the team has shown the PIX mechanism can refine grain structure in varied materials systems.

Knowles said alloys can be designed so that strain is generated internally during heat treatment. He said this opens possibilities for materials that are difficult to process by conventional methods, including refractory metals such as tungsten and advanced alloys for aerospace use, particularly for net-shape manufacturing.

Grain size has a major influence on how a material performs. Large grains can give cracks an easier path to spread, while smaller grains create more barriers, which can improve mechanical reliability and resistance to damage.

Tungsten is regarded as a leading candidate material for future fusion reactors because of its heat resistance and its very high melting point of 3,422 degrees Celsius. It can be brittle, however, and radiation exposure can make that brittleness worse. PIX offers another route to improving grain size in tungsten-based alloys intended for extreme environments.

Ageing the tungsten-chromium alloy at 1,250 degrees Celsius generated enough internal stress to drive recrystallisation, cutting average grain size by about 60 percent.

The same principle was demonstrated in a titanium-iron-molybdenum bcc-superalloy, a class of material under study for high-performance aerospace parts such as jet-engine compressor blades. Ageing that alloy at 750 degrees Celsius reduced its average grain size by about 90 percent and raised hardness by 60 HV.

The researchers suggest PIX may be a broader materials-design principle that could apply across different alloy systems, giving a new way to control grain structure and properties through heat treatment. It could be particularly useful for materials that are brittle, hard to shape, or made by additive manufacturing, where traditional rolling and deformation may not be practical.

CONTACT: https://doi.org/10.1038/s43246-026-01327-2