Achieving Complex Nanostructures: The Role of Hydrogen in Controlling Mechanical Alloying and Microstructure Evolution in the TiVZrNbHf-Cu System.

Hydrogen is key in reducing greenhouse gas emissions in materials production. At the same time, it significantly affects mechanical properties, often causing unwanted embrittlement. However, rather than solely addressing these disadvantages, hydrogen's inevitable role in sustainable metallurgy should be leveraged to create new and potentially superior materials. Here, it is shown that using hydrogen in the form of metal hydrides introduces a barrier to mechanical alloying, stabilizing otherwise unattainable microstructures. Severe plastic deformation of a composite of the equiatomic high entropy alloy (HEA) TiVZrNbHf and Cu leads to amorphization, while substituting the HEA with its hydride preserves the two-phase structure. Monte Carlo simulations confirm that the significantly different hydrogen affinities, together with the restricted dislocation motion in the hydride, create a barrier to mechanical alloying. This hydride route could enable new microstructure states, even in well-studied material systems. It opens an additional dimension in designing materials containing phases with diverging hydrogen affinities, offering tighter control over mechanical alloying.