Extraordinary Nanocrystalline Pb Whisker Growth from Bi-Mg-Pb Pools in Aluminum Alloy 6026 Moderated through Oriented Attachment.

Matic Jovičević-Klug,Bojan Podgornik,Tina Sever,Patricia Jovičević-Klug,Darja Feizpour

doi:10.3390/nano11071842

Matic Jovičević-Klug, Bojan Podgornik + Show 3 more

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https://doi.org/10.3390/nano11071842

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Abstract

The elucidation of spontaneous growth of metal whiskers from metal surfaces is still ongoing, with the mainstream research conducted on Sn whiskers. This work reports on the discovery of Pb whisker growth from Bi-Mg-Pb solid pools found in common machinable aluminum alloy. The whiskers and hillocks display unique morphologies and complex growth that have not been documented beforehand. In contrast to typical understanding of whisker growth, the presented Pb whiskers show a clear nanocrystalline induced growth mechanism, which is a novel concept. Furthermore, the investigated whiskers are also found to be completely composed of nanocrystals throughout their entire length. The performed research gives new insight into nucleation and growth of metal whiskers, which raises new theoretical questions and challenges current theories of spontaneous metal whisker growth. Additionally, this work provides the first microscopic confirmation of recrystallization growth theory of whiskers that relates to oriented attachment of nanocrystals formed within an amorphous metallic matrix. The impact of mechanical stress, generated through Bi oxidation within the pools, is theoretically discussed with relation to the observed whisker and hillock growth. The newly discovered nanocrystalline growth provides a new step towards understanding spontaneous metal whisker growth and possibility of developing nanostructures for potential usage in sensing and electronics applications.

Highlights

Published: 16 July 2021Metal whisker formation has been extensively researched within the last 50 years as they are the major cause of electrical shorts, and failure of electronic devices [1]
Pb whiskers display stepwise growth activation as well as temporal widening of a preexisting whisker through additional facete activation, which is a significantly different growth behavior compared to the growth of conventionally found whiskers in Sn materials
The combination of whisker and hillocks growth from a narrower opening and modification of the growth through the widening and narrowing of the whiskers is associated to a complex growth mechanism that results in unique whiskers and hillocks morphologies

Summary

Introduction

Published: 16 July 2021Metal whisker formation has been extensively researched within the last 50 years as they are the major cause of electrical shorts, and failure of electronic devices [1]. Several researchers have provided results that contradict these theories and discussed that other mechanisms are potentially involved in the formation of metal whiskers (see comprehensive review by Zhang et al [1]). One of these mechanisms is the recrystallization theory, which was firstly proposed by Ellis et al [8] and was one of the theories that disproved the prior dislocation driven whisker growth theories designed by Frank [9] and Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

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