This research focuses on tin whisker growth under two different environmental conditions namely hygrothermal and a salt solution. Tin coated brass coupons were used for this study to analyze the growth of tin whiskers over time. Their growth rates were examined periodically using optical and scanning electron microscopy. The physical characteristics of the tin whiskers were identified for each environmental condition. It was discovered that submersion of tin coated brass substrates in 5% salt solution considerably increased the density (number of whiskers per unit area), and the length of the whiskers. In addition, it was found that the geometry and aspect ratio of tin whiskers were different for each environment.

The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200˚C, 300˚C, 350˚C and 400˚C before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200˚C preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness K I for the parent rail was 127 MPa.m 0.5 , while that for the optimum welded joint (200˚C preheat) was 116.5 MPa.m 0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200˚C preheat.

Microstructure and fracture behavior of ASTM 572 Grade 65 steels used for wind tower applications have been studied. Steels of two carbon level chemistries designed for this grade were used in the study. Fracture toughness of the steels was studied using 3-point bend test on samples coated with zinc and not coated with zinc. Lower carbon steel showed higher resistance to fracture than medium carbon steel after zinc galvanization. SEM study suggests that zinc and zinc bath additives that migrated to crack tips are responsible for the loss in ductility. The phenomenon of Liquid Metal Embrittlement (LME) is suggested to have taken place. Zinc bath additives traced at crack zones are suggested to have migrated at the zinc galvanizing temperatures

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.