Diode leads that were to be made from OFHC copper were instead made from copper with high oxygen content. The leads had a nickel underplating, a gold final plating, and were brazed to the diode package in a hydrogen atmosphere. After brazing, the leads became embrittled. SEM examination of the fractured leads revealed voids and some oxidized areas surrounded by ductile fracture areas. High pressure steam pockets observed as voids in the microstructure caused hydrogen embrittlement of the leads. The obvious corrective action was to ensure that the lead material was OFHC copper.

A shotgun barrel fabricated from 1138 steel deformed when test firing alternative nontoxic ammunition. The test shells contained soft iron shot, which at 72 HB, is much harder than traditional lead shot (typically 30 to 40 HB). An investigation based on ID and OD profiling supported the conclusion that the iron shot increased stresses in the choke zone of the barrel, causing it to deform. Variations in the amount of bulging were attributed to a lack of uniformity in wall thickness. Recommendations included making the barrel from steel with a higher yield strength, making the barrel walls thicker and more uniform, and/or developing an alternative nontoxic metal shot with a hardness in the range of 30 to 40 HB.

Severely reduced wall thickness was encountered at the liquid line of a lead-bath pan that was used in a continuous strip or wire oil-tempering unit. Replacement of the pan was necessary after six months of service. The pan, 6.9 m (22.5 ft) long, 0.6 m (2 ft) wide, and 38 cm (15 in.) deep with a 2.5-cm (1-in.) wall thickness, was a type 309 stainless steel weldment. Operating temperatures of the lead bath in the pan ranged from 805 deg C (1480 deg F) at the entry end to 845 deg C (1550 deg F) at the exit end. Analysis (visual inspection. metallographic analysis, moisture testing, and etched micrographs using Murakami's reagent) supported the conclusions that thinning of the pan walls at the surface of the molten lead resulted from using coke of high moisture content and from the low fluctuating coke level. Recommendations included reducing the supply of oxygen attacking the grain boundaries and the hydrogen that readily promoted decarburization with the use of dry (2 to 3% moisture content) coke. Maintaining a thick layer of coke over the entire surface of molten lead in the pan would exclude atmospheric oxygen from the grain boundaries.

Examination of a connecting-rod shell bearing from a six-cylinder gasoline engine was done after it was returned to the factory. Copper-lead alloy SAE 485 bonded to a low-carbon steel backing was used to make the bearing and the oil used in the engine was the recommended one. Measurable material loss was visible over most of the bearing halves particularly in a wide region at the centerline. A brittle waxlike substance identified to be a mixture of copper and lead sulfides covered the visible shallow pits and the darkened region. Change of oil with greater frequency to prevent the buildup of sulfur compounds or bearing halves that have corrosion-resistant overlay materials were recommended as best solutions.

The working fluid of a hypersonic wind tunnel is freon 14 heated in molten-metal-bath heat exchangers. The coils of the heaters have failed several times from various causes. They have been replaced each time with a stainless steel deemed more appropriate, but they continue to fail. In this case study, the history of failures is traced, the causes are analyzed, and recommendations are made for future design and maintenance. Coils fabricated from AISI 316 should provide satisfactory service life if reasonable precautionary measures are observed during maintenance and testing.

Cracks were found on the wing leading edge of a test aircraft made from AZ31B magnesium alloy. Crack lengths were approximately 230 mm (9 in.) long on the left side and approximately 130 mm (5 in.) long on the right side. The cracks ran parallel to the leading edge. The 230-mm (9-in.) crack was received for examination. Visual examination of the submitted panel revealed two cracks. One crack ran through six adjacent fastener holes. Sections of the beveled edges of the holes were missing and corrosion was evident. Visual examination of the fastener holes after separation of the crack showed that the fracture faces were corroded. Optical examination of either side of the middle group of fastener holes showed that the area of suspected crack initiation had suffered excessive corrosion. Examination of the holes on the end of the crack showed fracture characteristics typical of fatigue and/or corrosion fatigue. It was concluded that crack propagation of the fracture in the wing panel occurred by a combination of corrosion and high-cycle fatigue in the end fastener holes. It was recommended that future panels be manufactured of 2024 aluminum.

A large crack developed at a girder-truss joint area of the Fremont bridge in Portland, OR, on 28 Oct 1971. It occurred during a positioning procedure involving a junction piece welded to a girder, starting as a brittle fracture and terminating in plastic hinges in the girder web welds. The arch rib top plate, as it met the main girder, formed a composite beam of A588/A36 composition. Investigation showed the original design of the failed component called for an angle of high geometric stress concentration (90 deg with no radius) in a region of substantial transverse weld joints. While the material met chemical and mechanical property requirements, tests showed it had low fracture toughness and critical-sized flaws oriented normal to the principal stress in the failed junction piece. Fabrication procedures resulted in high residual stresses and a metallurgical notch at the radius in the junction piece. Stresses induced during jacking (the procedure used to raise bridge components into position) applied the stresses in the critical radius that triggered the cracking.

After six years of service, three water shut-off valves on a copper water line in a residential building were found to be inoperative. Macroscopic examination of the valves after disassembly revealed that all three failed at the key that holds the spindle in the gate. In addition, the color near the key changed from yellow to red-brown. The gate was made from leaded red brass (85-5-5-5) while the spindle was made from silicon brass. It was concluded that the valves failed by dezincification resulting from bimetallic galvanic corrosion. It is common in the valve industry to use components made of different alloys in the same valve, but this is not the best approach for all applications.