Kinetics of the lattice response to hydrogen absorption in thin Pd and CoPd films

TL;DR

This study investigates the kinetics of lattice expansion in thin Pd and CoPd films due to hydrogen absorption, revealing irreversible inflation, shape memory effects, and modeling the plastic creep with an Avrami-type nucleation and domain growth model.

Contribution

It demonstrates that the lattice response in thin Pd and CoPd films to hydrogen absorption involves irreversible inflation and shape memory, modeled by an Avrami-type nucleation process.

Findings

Irreversible inflation of films under hydrogen exposure

Controllable shape memory effects observed

Plastic creep dynamics fit an Avrami-type nucleation model

Abstract

Hydrogen can penetrate reversibly a number of metals, occupy the interstitial sites and cause large expansion of the crystal lattice. The question discussed here is whether the kinetics of the structural response matches hydrogen absorption. We show that thin Pd and CoPd films exposed to a relatively rich hydrogen atmosphere (4% H2) inflate irreversibly, demonstrate the controllable shape memory, and duration of the process can be orders of magnitude longer than hydrogen absorption. The dynamics of the out-of-equilibrium plastic creep is well described by the Avrami - type model of the nucleation and lateral domain wall expansion of the swelled sites.