A commercial hybrid-iron golf club fractured during normal use. The club fractured through its cast aluminum alloy hosel. Optical analysis revealed casting pores through 20% of the hosel thickness. Mechanical properties were determined from characterization results, then used to construct a finite element model to analyze material performance under failure conditions. In addition, a full scale structural test was conducted to determine failure strength. It was concluded that the club failed not from ground impact but from a force reversal at the bottom of the downswing. Large moments generated during the downswing aggravated by manufacturing defects and stress concentration combined to create an overload condition.

This article presents a failure analysis of an aluminum cylinder head on an automotive engine. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head, then propagated through the entire thickness of the component. Metallurgical examination of the crack origin revealed that casting pores played a role in initiating the crack. Stress components, identified by finite element analysis, also played a role, particularly the stresses imposed by the bolt assembly leading to plastic strain. It was concluded that the failure can be prevented by eliminating the bolt hole, using a different type of bolt, or adjusting the fastening torque.

The paper describes the findings from a damaged propeller blade made from Mn-Ni-Al-bronze, commercially known as Superston 70 (ABS Type 5). The blade had broken at the 0.65 pitch radius location, and the fracture occurred in a brittle mode. The findings reported here point to two potential contributors to the propeller blade failure, viz., the presence of casting flaws at the low pressure side of the propeller blade and service stresses at this surface that reached approximately 400 MPa. This stress value exceeded the yield strength at the corresponding location of the unbroken blade by approximately 40%.

To ensure no malfunctions and although there were no apparent problems, a main fuel control was returned to the factory for examination after service on a test aircraft engine that had experienced high vibrations. When the fuel control was disassembled, a lever, cast from AMS 5350 (AISI type 410) stainless steel that was through-hardened to 26 to 32 HRC and passivated, was shown to be cracked. The crack initiated at the sharp corner of the elongated milled slot and propagated across to the outer wall. The sections around the crack were spread about 30 deg apart, showing the fracture surface under investigation had beach marks initiating at the sharp corner along the milled slot. Changes in frequency or amplitude of vibration caused different rates of propagation, resulting in a change in pattern. This evidence supported the conclusion that the lever failed in fatigue as a result of excessive vibration of the fuel control on the test engine. Recommendations included redesign of the lever with a large radius in the corner where cracking originated. This would reduce the stress-concentration factor significantly, thus minimizing the susceptibility of the lever to fatigue.

A lever (machined from a casting made of AISI type 410 stainless steel, then surface hardened by nitriding) that was a component of the main fuel-control linkage of an aircraft engine fractured in flight after a service life of less than 50 h. Investigation (radiographic inspection) supported the conclusions that the lever broke at a cold shut extending through approximately 95% of the cross section. The normally applied load constituted an overload of the remainder of the lever. Recommendations included adding magnetic-particle inspection to the inspection procedures for this cast lever.

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.

After 14 months of service, cracks were discovered in castings and bolts used to fasten together braces, posts, and other structural members of a cooling tower, where they were subjected to externally applied stresses. The castings were made of copper alloys C86200 and C86300 (manganese bronze). The bolts and nuts were made of copper alloy C46400 (naval brass, uninhibited). The water that was circulated through the tower had high concentrations of oxygen, carbon dioxide, and chloramines. Analysis (visual inspection, bend tests, fractographs, 50x unetched micrographs, 100x micrographs etched with H4OH, and 500x micrographs) supported the conclusions that the castings and bolts failed by SCC caused by the combined effects of dezincification damage and applied stresses. Recommendations included replacing the castings with copper alloy C87200 (cast silicon bronze) castings. Replacement bolts and nuts should be made from copper alloy C65100 or C65500 (wrought silicon bronze).

A desuperheater diffuser nozzle in the steam supply line failed within nine months of service in an 8.25 MN/sq m (1200 psig) steam line. The nozzle was an austenitic stainless steel casting in conformance to material. The nozzle had numerous cracks on the inside and outside surfaces, and the cracks had penetrated through the wall thickness in several areas. The fracture surfaces had distinct beach markings delineating the crack front, representative of crack propagation stages. The cracks were transgranular and, unlike classical corrosion-fatigue cracks, exhibited branching, characteristic of chloride-induced SCC in austenitic stainless steels. The failure resulted from chloride-induced SCC, possibly assisted by cyclic stress. The recommendation for alternate material for the desuperheater nozzle included nickel base alloys per ASTM B 564, Grades 600 or 800 titanium alloy per ASTM B 367, Grades C3/C4, or ferritic stainless steel alloy per ASTM 182, Grade FXM27.

Two steam-methane reformer furnaces were subjected to short-time heat excursions because of a power outage, which resulted in creep bulging in the Incoloy 800 outlet pigtails, requiring complete replacement. Each furnace had three cells, consisting of 112 vertical tubes per cell, each filled with a nickel catalyst. The tubes were centrifugally cast from ASTM A297, grade HK-40 (Fe-25Cr-20Ni-0.40C), heat-resistant alloy. The tube was concluded after metallurgical inspection to have failed from creep rupture (i.e., stress rupture). A project for detecting midwall creep fissuring was instigated as a result of the failure. It was concluded after laboratory radiography and macroexamination that if the fissure were large enough to show on a radiograph, either with or without the catalyst, the tube could be expected to fail within one year. The set up for in-service radiograph examination was described. The tubes of the furnace were radiographed during shut down and twenty-four tubes in the first furnace and 53 in the second furnace showed significant fissuring. Although, radiography was concluded to be a practical technique to provide advance information, it was limited to detecting fissures caused by third-stage creep in tubes because of the cost involved in removing the catalysts.

Two water pumps were taken out of service because of reduced output. Visual inspection revealed considerable material loss in both impellers, which were 25.4 cm (10 in.) in diam x 1.3 cm (0.5 in.) wide and made from a cast bronze alloy. Several similar water pumps operating under nearly identical conditions, drawing water from an open tank through a standpipe, had no observable failures. Etched micrographs 100x of samples taken from the impellers showed clean, pockmarked, severely eroded surfaces, characteristic of cavitation damage. Investigation also revealed that considerable quantities of air were being drawn into the system when water in the supply tank dropped below a certain level. It was concluded that cavitation erosion (due to the uptake of air) caused metal removal and microstructural damage in the impellers. Recommendations included adding a water-level control to the piping system and excluding air from the pump inlet.

Stator vanes (cast from a Cu-Mn-Al alloy) in a hydraulic dynamometer used in a steam-turbine test facility were severely eroded. The dynamometer was designed to absorb up to 51 MW (69,000 hp) at 3670 rpm, and constituted an extrapolation of previous design practices and experience. Its stator was subject to severe erosion after relatively short operating times and initially required replacement after each test program. Although up to 60 cu cm (3.7 cu in.) of material was being lost from each vane, it only reduced the power-absorption capacity by a small amount. Analysis supported the conclusion that the damage was due to liquid erosion, but it could not be firmly established whether it was caused by cavitation or by liquid impact. Recommendations included making a material substitution (to Mo-13Cr-4Ni stainless steel) and doing a redesign to reduce susceptibility to erosion as well as erosion-producing conditions.

A failure analysis was conducted in late 1996 on two rolls that had been used in the production of iron and steel powder. The rolls had elongated over their length such that the roll trunnions had impacted with the furnace wall refractory. The result was distortion and bowing of the roll bodies which necessitated their removal from service. The initial analysis found large quantities of nitrogen had been absorbed by the roll shell. Further research indicated nitrogen pickup accounted for 3% volumetric growth for every 1% by weight nitrogen absorption. This expansion was sufficient to account for the dimensional change observed in the failed rolls. This paper details the failure analysis and resulting research it inspired. It also provides recommendations for cast material choice in highly nitriding atmospheres.

A microstructural analysis has been made of a burner nozzle removed from service in a coal gasification plant. The nozzle was a casting of a Co-29wt%Cr-19wt%Fe alloy. Extensive hot corrosion had occurred on the surface. There was penetration along grain boundaries, and corrosion products in these regions were particularly rich in S, and also contained Al, Si, O, and Cl. The grain boundaries contained Cr-rich particles which were probably Cr23-C6 type carbides. In the matrix, corrosion occurred between the Widmanstatten plates. Particles were found between these plates, most of which were rich in Cr and O, and probably were Cr2-O3 oxides. Other matrix particles were found which were rich in Al, O, and S. The corrosion was related to these grain boundary and matrix particles, which either produced a Cr-depleted zone around them or were themselves attacked.

During periodic inspection of the tubes of a reformer furnace, a soapy water leak test with the tubes pressurized with nitrogen was being carried out by site personnel in a manner contrary to the policy of the organization when one of the tubes suddenly disintegrated with explosive violence. The tube approximately 30 ft. long by 6 in. diam, was constructed of three spun cast sections butt welded together. The material specified for tubes for this service was basically a 25% chromium, 20% nickel, cast stainless steel containing 0.4% carbon to optimize creep resistance. Failure initiated in the region of the tube where the dark fracture surface and columnar grain structure were evident. These features indicated the presence of a defective zone or progressive cracking which had occurred during service. Microscopic examination of sections through the zone revealed extensive creep cracking. The cracking was intergranular and followed the interdendritic columnar structure adjacent to the outer surface.

Lakes in zinc die castings are areas encompassed by irregular lines or waves on flat or slightly contoured surfaces which are intended to look uniform. The laked areas have to be removed by polishing before the castings can be plated. This adds considerably to the overall cost of production. Castings examined were of an automobile name-plate holder with two flat sides of approximately 113 sq cm. All castings produced during a trial showed laking defects, the number and position varying from casting to casting. It was found that formation of metal waves and lakes depended primarily on the design of the gate and runner system and operating conditions. High flow efficiencies, with adequate feeding to all sections of the die, and short cavity fill times are desirable.

Persistent leakage was experienced from copper tube heaters which formed part of dairy equipment. Metallurgical examination of the brazed joints showed them to have suffered a preferential corrosion attack. This resulted in the phosphide phase of the brazing alloy being corroded away, leaving a weak, porous residual structure. The brazing alloy was of type CP 1 as covered by BS 1845. Header and tube materials were basically copper-nickel alloys for which the use of a phosphorus bearing brazing alloy is not recommended owing to the possibility of forming the brittle intermetallic compound, nickel phosphide. The use of a brazing alloy containing phosphorus was unsuitable on two counts and a quaternary alloy containing silver, copper, cadmium and zinc, such as those in group AG1 or AG2 of BS 1845 would be more suitable. However, because corrosive problems experienced in these units indicated severe service conditions, a proprietary alloy similar to AG1, but containing 3% nickel, was recommended.

The origins of the casting are unknown. It is included here as a classic case of intergranular corrosion. The part (apparently a pump outlet) was named the “rubber casting” because of the severity of the intergranular attack. Every grain boundary has been attacked to the extent that the casting could be twisted and stretched as through made of rubber. The chemistry of the casting was acceptable for CN-7M. The reason the part failed is a continuous film of carbide with a continuous crack running parallel to the carbides. This sensitized structure produces an area depleted in protective chromium, making it susceptible to corrosion. Two solutions to this problem are available. The simplest is to ensure correct heat treatment to dissolve grain-boundary carbide film and return the protective chromium to the depleted zone. Alternatively, a low-carbon (0.03% maximum C, for example, CF-3) grade can be specified. Procedures are given in a reference for screening castings that may be susceptible to intergranular corrosion due to processing errors.

In a housing made of cast steel GS 20MoV12 3, weighing 42 tons, precipitates were found on the austenitic grain boundaries during metallographic inspection. According to their shape and type they were recognized as carbides that precipitated during tempering. In addition, a much coarser network of rod-shaped and plate-shaped precipitates was found, that probably corresponded to the primary grain boundaries, or to the grain boundaries or twin planes of the austenite formed during solidification of the melt. These particles could have been aluminum nitride judging by their shape and order of precipitation. Tests showed that a subsequent removal of this defect by solutioning was impractical because the annealing temperature was too high. To avoid this defect in the future the sole recommendation is to accelerate the cooling rate through the critical region between 1200 to 900 deg C to such an extent as is practicable with respect to machinability.

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 steam tug Hercules was an ocean-going and bay tug for 55 years before being retired. It is now being restored by the National Park Service. A broken steam valve was obtained for microstructural examination. The body was gray cast iron, and the stem and seat were brass. The examination centered on corrosion of the brass components. The seat and shaft were alpha brass, with a hardness of 64 and 79 DPH, respectively. A nut held the shaft onto the seat, and was alpha-beta brass with a hardness of 197 DPH. Welded on the end of the shaft was a ring of hard (DPH 294) alpha-beta brass, which seated against the nut. The brass seat and stem show little corrosion. However, the alpha-beta brass nut and welded tip showed extensive dezincification. This process of removal of Zn and the retention of Cu began in the high Zn beta phase, but eventually both phases were attacked. The depth of penetration was consistent with dezincification rates reported in the literature for such brasses in salt water if the valve had been in service about 55 years.