Kinetics of intrinsic stress in nanocrystalline films

Enrique Vasco,María J Ramírez-Peral,Alfredo Jacas-Rodríguez,Celia Polop

doi:10.1016/j.scriptamat.2021.114015

Abstract

Conventional polycrystalline materials acquire high levels of intrinsic mechanical stress (ranging from MPa to a few GPa) during preparation and use, but this stress decays quickly (~minutes) to small residual values (~kPa) under standard resting conditions. Nanocrystalline materials reach similar or even higher levels of intrinsic stress, but surprisingly retain a significant portion of this stress over much longer time scales (~hours). This behavior directly contradicts current theoretical models that predict stress relaxation through diffusive currents. Diffusive currents, which flow mainly on the surfaces of grains, are expected to produce faster relaxation kinetics when the stress to be released is higher. In this work, we study the kinetics of intrinsic stress relaxation in nanocrystalline films and identify the limitations of this process as a preliminary step towards designing a strategy for high-stress stabilization in nanostructured systems.

Highlights

The origin and dynamics of intrinsic compression in polycrystalline films and coatings has been intensively studied for decades [1], yet some experimentally verified features of this phenomenon still have no convincing theoretical explanation
Intrinsic compression is correlated with the presence of grain boundaries, which alter the surface kinetics of these systems under conditions of high atomic transport [2,3,4]
Nanocrystalline films exhibit huge intrinsic compressions; their relaxation kinetics are much slower than expected, and their stress levels are retained longer than the lower stress levels observed in films with larger grains [5]

Summary

Introduction

The origin and dynamics of intrinsic compression in polycrystalline films and coatings has been intensively studied for decades [1], yet some experimentally verified features of this phenomenon still have no convincing theoretical explanation. Once the condition of high atomic transport is removed, the intrinsic compression relaxes via currents of adatoms driven by gradients of stress [7,8] and/or strain energy [9,10].

Results

Conclusion