Date of Award

2024

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Materials Science and Engineering (MS)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Paul G. Sanders

Committee Member 1

Douglas J. Swenson

Committee Member 2

Vinh T. Nguyen

Abstract

Every year, thousands of cast-steel railcar couplers suffer from corrosion-initiated fatigue cracking in similar areas of the coupler’s knuckle; between 2015 and 2018 about 90,000 knuckles were replaced, otherwise these couplers would have been at risk for unexpected failures. These types of couplers have been common in industrial use as early as 1932, hence it is desirable for a countermeasure to the fatigue cracking that does not involve significantly altering the geometry or casting process. Wire arc additive manufacturing (WAM) is a developing technology which boasts the ability to produce complex near-net-shape components; however, less attention has been paid to WAM’s potential for local enhancements to typical failure zones. By replacing the cast steel in the region of the knuckle that contains these high-stress failure points with fatigue and corrosion resistant WAM deposits, the whole knuckle receives a longer service life while maintaining its mechanical properties and overall geometry. The efficacy of this procedure comes down to the ability to print WAM deposits with less defects than the base steel while introducing alloying elements (nickel, chromium, molybdenum) to prevent corrosion; this is accomplished by utilizing gas tungsten arc welding (GTAW) in the WAM process with commercially available low-alloy filler wire prior to optimization using the knuckle’s heat treat schedule then validated by fatigue testing the resulting components. Selective use of WAM technology to aid in the high-volume production of parts through local enhancements could be a step to efficiently utilize its capabilities in industry.

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