Failure Analysis of Metallic Components of a Battery Fitted in a Naval System
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CASE HISTORY—PEER-REVIEWED
Failure Analysis of Metallic Components of a Battery Fitted in a Naval System Mrityunjoy Hazra . Satyapal Singh
Submitted: 16 January 2019 / Accepted: 8 August 2019 Ó ASM International 2019
Abstract A battery based on Mg–AgCl with sea water as electrolyte was developed for propulsion of a naval system. In one occasion, the tie rod, conduit pipe and the copper bus rod each covered with polymer sleeve were found damaged. The copper bus rod was melted probably by amplified resistance and subsequent heating. Localized cross-sectional reduction (and thus increased resistance, R) seems to have aggravated heating by Joule heating (J = I2R) effect. Subsequently, it led to partial dissolution, embrittlement, softening and final fracture of the steel tie rod in the said sequence. There was no material deficiency. Chemical composition, microstructure and hardness values of the failed components indicate that the steel tie rod was made of the as-specified EN 24 type of low alloy steel in hardened and tempered condition, while copper bus rods were made of pure copper of 99.50% purity. Damage of the conduit tube was not related to the failure of steel tie rod and copper bus rod, although it indirectly offers clues that melting of copper happened and the molten copper reached many locations within the system. Keywords Failure Metallic component Battery Liquid metal embrittlement (LME) En 24 steel Copper bus rod
M. Hazra (&) S. Singh Defence Metallurgical Research Laboratory (DMRL), P.O. – Kanchanbagh, Hyderabad 500 058, India e-mail: [email protected]; [email protected]
Introduction A battery based on Mg–AgCl with sea water as electrolyte was developed for propulsion of a naval system. The construction of this battery involves steel tie rods, titanium conduit pipes and copper bus rods (Fig. 1), and each of these components was covered with a polymer sleeve. In one occasion during start of a trial, the tie rod, conduit pipe and the copper bus rod were found damaged. The damaged parts were received at this laboratory for investigation on cause of the damage.
Experimental Procedure The failed steel tie rod, copper bus rods and titanium conduit pipe were, at first, examined visually by naked eye and under magnifying glass. Photographs in the as-received condition were taken and preserved for future reference, during the course of analysis. The failed parts were then sectioned from the main components for its further analysis. Later, those parts were put under forced air using airblower to remove the loosely adhered particles and then examined under scanning electron microscope (SEM). Fracture surface was cleaned ultrasonically in acetone after examination on probable surface corrosion debris and/or contamination, before fractographic study. Branson solution was used for removal of thick corrosion product so as to reveal the fractograph in a better way. After that, representative cross-sectional sample extraction from failed parts was carried out from near to the failed surface a
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