Zirconium metals deform in surprisingly complex ways under extreme conditions

Materials are essential to modern technologies, especially those used in extreme environments such as nuclear power systems and military applications. These materials must withstand intense pressures, temperatures, and corrosion. Understanding their lattice-level behavior under such conditions is essential to developing next-generation materials that are stronger, cheaper, lighter, and more durable.

Scientists and collaborators at Lawrence Livermore National Laboratory (LLNL) compressed single-crystal samples of zirconium and found that under high pressure, the material deformed in surprisingly complex ways. The research is published in two journals, Physical Exam Letters And Physical examination B.

Materials under high stress conditions relieve shear stress through mechanisms such as dislocation glide, crystallographic twinning, shear-induced amorphization, phase transition, and fracture.

“Understanding these microscopic mechanisms is essential for developing predictive models of materials performance,” said Saransh Soderlind, a LLNL scientist and lead author of the study. Physical Exam Letters.

All metals undergo plastic deformation, that is, they change shape permanently, under compression, mainly due to the movement of defects called dislocations on certain planes in specific crystallographic directions. In the case of zirconium, the complexity is even greater due to a change in the crystal structure under pressure.

“Precise knowledge of the crystallographic planes and the direction in which a material deforms can allow us to develop models that describe the mechanical behavior of metals at extreme levels of compression,” Soderlind said. “In our work on zirconium, we used new experimental techniques that revealed how elemental metals deform in unexpected and extremely complex ways.”

The team used in situ femtosecond X-ray diffraction to observe the behavior of single-crystal zirconium compressed at high pressure on nanosecond time scales. The team detected the presence of atomic disorder, a phenomenon never before observed in an elemental metal, and discovered several pathways for transformation of the crystal structure, another first of its kind.

This disorder and multiple phase transition pathways have not been observed in polycrystalline zirconium, adding to the novelty of the study. Multimillion-atom molecular dynamics simulations using a machine-learned potential corroborated the experimental observations in the study.

“These results reveal a more complex picture of metal deformation under extreme conditions than previously thought. This rich mosaic of atomic motions is likely common in other high-pressure materials,” said LLNL scientist Raymond Smith.

Zirconium alloys are used in the nuclear industry as fuel rod cladding due to their high strength and low neutron absorption cross-section. They are also widely used in extreme chemical environments.