Fasteners, made in high-production progressive dies from 0.7 mm thick cold-rolled 1060 steel, were used to secure plastic fabric or webbing to the aluminum framework of outdoor furniture. It was found that approximately 30% of the fasteners cracked and fractured as they were compressed to clamp onto the framework prior to springback. The heat treatment cycle of the fasteners consisted of austenitizing, quenching, tempering to obtain a tempered martensite microstructure, acid cleaning, zinc electroplating, coating with a clear dichromate and thereafter baking to remove the nascent hydrogen. It was revealed that fasteners treated in this manner were brittle due to hydrogen embrittlement as the baking process was found to not be able to remove all the nascent hydrogen which had induced during acid cleaning and electroplating. The heat treatment cycle was modified to produce a bainitic structure and the method of plating the fastener with zinc was changed from electroplating to a mechanical deposition process to thus avoid hydrogen embrittlement.

During an inspection of a structure two weeks after assembly, the heads of several cadmium-plated AISI 8740 steel fasteners were found to be completely separated from their respective shanks. SEM examination of the fracture surfaces revealed a brittle, intergranular fracture mode, indicating hydrogen embrittlement. An investigation was conducted to determine the extent of hydrogen embrittlement in the various lots of cadmium-plated 8740 steel fasteners. It was found that hydrogen embrittlement was caused by the use of a bright, impervious cadmium electroplate that hindered diffusion of mobile hydrogen outward from the surface of the pin. After the cadmium layer was removed, the mobile hydrogen contained on the surface of the steel and in the electroplated deposit was released, and the embrittlement problem was alleviated. To prevent reoccurrence, the bright cadmium layer was stripped from the pins, which were then baked and repeated with a dull, porous cadmium layer that allowed outward diffusion of hydrogen. The pins were baked again after deposition of the porous cadmium layer. This eliminated the problem.

Socket head cap screws used in a naval application were failing in service due to delayed fracture. The standard ASTM A 574 screws were zinc plated and dichromate coated. Investigation (visual inspection, 1187 SEM images, chemical analysis, and tension testing) of both the failed screws and two unused, exemplar fasteners from the same lot supported the conclusion that the cap screws appear to have failed due to hydrogen embrittlement, as revealed by delayed cracking and intergranular fracture morphology. Static brittle overload fracture occurred due to the tension preload, and prior hydrogen charging that occurred during manufacturing. The probable source of charging was the electroplating, although postplating baking was reportedly performed as well. Recommendations included examining the manufacturing process in detail.

The electroplated tappet adjusting screws used in diesel engines failed during initial bend testing. The analysis of the failure showed that the fracture was nucleated from the subsurface of the screw. The fracture surface was intergranular at the ID and OD region and microvoid coalescence in the center. The improper baking after electroplating of the screw led to H2-induced blistering/cracking. The high strength of the threaded region of the adjusting screw increased the failure propensity.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

This article discusses different types of mechanical fasteners, including threaded fasteners, rivets, blind fasteners, pin fasteners, special-purpose fasteners, and fasteners used with composite materials. It describes the origins and causes of fastener failures and with illustrative examples. Fatigue fracture in threaded fasteners and fretting in bolted machine parts are also discussed. The article provides a description of the different types of corrosion, such as atmospheric corrosion and liquid-immersion corrosion, in threaded fasteners. It also provides information on stress-corrosion cracking, hydrogen embrittlement, and liquid-metal embrittlement of bolts and nuts. The article explains the most commonly used protective metal coatings for ferrous metal fasteners. Zinc, cadmium, and aluminum are commonly used for such coatings. The article also illustrates the performance of the fasteners at elevated temperatures and concludes with a discussion on fastener failures in composites.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

Several surface-mount chip resistor assemblies failed during monthly thermal shock testing and in the field. The resistor exhibited a failure mode characterized by a rise in resistance out of tolerance for the system. Representative samples from each step in the manufacturing process were selected for analysis, along with additional samples representing the various resistor failures. Visual examination revealed two different types of termination failures: total delamination and partial delamination. Electron probe microanalysis confirmed that the fracture occurred at the end of the termination. Transverse sections from each of the groups were examined metallographically. Consistent interfacial separation was noted. Fourier transform infrared and EDS analyses were also performed. It was concluded that low wraparound termination strength of the resistors had caused unacceptable increases in the resistance values, resulting in circuit nonperformance at inappropriate times. The low termination strength was attributed to deficient chip design for the intended materials and manufacturing process and exacerbated by the presence of polymeric contamination at the termination interface.

Aircraft missile launcher attachment bolts fabricated from cadmium-coated Hy-tuf steel were found broken. Subsequent analysis of the broken bolts indicated three causes of failure. First, the bolts had been carburized, which was not in conformance with the heat treating requirements. Second, macroetching showed that the bolts has been machined from stock rather than forged, and the threads cut rather than rolled. It was also determined that hydrogen-assisted stress-corrosion cracking also played a part in the failure of the high-strength bolts.

Cadmium-coated type 410 martensitic stainless steel 1 4 -14 self-drilling tapping screws fractured during retorquing tests within a few weeks after installation. The screws were used to assemble structural steel frames for granite panels that formed the outer skin of a high-rise building. Fractographic and metallographic examination showed that the fractures occurred in a brittle manner from intergranular crack propagation. Laboratory and simulated environmental tests showed that an aqueous environment was necessary for the brittle fracture/cracking phenomenon. The cracks were singular and intergranular with little branching. Secondary subsurface cracks suggested possible hydrogen embrittlement. The 410 screws had been introduced to replace conventional case-hardened carbon steel screws that conform to SAE specification J78. Carbon steel screws had a proven record of acceptable performance for the intended application. It was recommended that use of the 410 screws be discontinued in preference to the case-hardened carbon steel screws.

Three wing flap hinge bearings were received by the laboratory for analysis. The bearings were fabricated from chromium-plated type 440C martensitic stainless steel. The intergranular fracture pattern seen in the electron fractographs, coupled with the corrosion pits observed on the inner diam of the bearings, strongly suggested that failure initiated by pitting and progressed by SCC or hydrogen embrittlement from the plating operation. It was recommended that the extent of the flap hinge bearing cracking problem be determined by using nondestructive inspection because it is possible to crack hardened type 440C during the chromium plating process. An inspection for pitting on the bearing inner diam was also recommended. It was suggested that electroless nickel be used as a coating for the entire bearing. A review of the chromium plating and baking sequence was recommended also to ensure that a source of hydrogen is not introduced during the plating operation.

Four cadmium-plated ASTM A193 grade B studs from a steam line connector associated with a power turbine failed unexpectedly in a nil-ductility manner. Fracture surfaces were covered with a light-colored, lustrous deposit. Optical microscope, SEM, and EDS analyses were conducted on sections from one of the studs and revealed that the coating on the fracture surface was cadmium. The fracture had multiple origins, and secondary cracks also contained cadmium. The fracture topography was intergranular. The failures were attributed to liquid metal embrittlement caused by the presence of a cadmium plating and operating temperatures at approximately the melting point of cadmium. It was recommended that components exposed to the cadmium be replaced.

Examination of several fighter aircraft main landing gear legs revealed unusual cracking in the hard chromium plating that covered the sliding section of the inner strut. The cracking was associated with cracks in the 35 NCD 16 steel beneath the plating. A detailed investigation revealed that the cracking was caused by the combination of incorrect grinding procedure, the presence of hydrogen, and fatigue. The grinding damage generated tensile stresses in the steel, which caused intergranular cracking during the plating cycle. The intergranular cracks were initiation sites for fatigue crack growth during service. It was recommended that the damaged undercarriage struts be withdrawn from service pending further analysis and development of a repair technique.

Hydrogen damage is a term used to designate a number of processes in metals by which the load-carrying capacity of the metal is reduced due to the presence of hydrogen. This article introduces the general forms of hydrogen damage and provides an overview of the different types of hydrogen damage in all the major commercial alloy systems. It covers the broader topic of hydrogen damage, which can be quite complex and technical in nature. The article focuses on failure analysis where hydrogen embrittlement of a steel component is suspected. It provides practical advice for the failure analysis practitioner or for someone who is contemplating procurement of a cost-effective failure analysis of commodity-grade components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also provided.

This article provides an overview of the classification of hydrogen damage. Some specific types of the damage are hydrogen embrittlement, hydrogen-induced blistering, cracking from precipitation of internal hydrogen, hydrogen attack, and cracking from hydride formation. The article focuses on the types of hydrogen embrittlement that occur in all the major commercial metal and alloy systems, including stainless steels, nickel-base alloys, aluminum and aluminum alloys, titanium and titanium alloys, copper and copper alloys, and transition and refractory metals. The specific types of hydrogen embrittlement discussed include internal reversible hydrogen embrittlement, hydrogen environment embrittlement, and hydrogen reaction embrittlement. The article describes preservice and early-service fractures of commodity-grade steel components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also reviewed.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

Several cadmium-plated carbon steel socket head cap screws that were part of a slide valve assembly on a regenerator line in a petrochemical plant failed during initial loading. Metallographic and XDS chemical analysis in conjunction with SEM examination of one failed and one unfailed cap screw indicated that the screws had failed by hydrogen embrittlement. The plating process was the likely source of the hydrogen. It was recommended that the remainder of the cap screws from the same lot as the failed screws be baked at approximately 190 deg C (375 deg F) for 24 h.

Uncoated high-strength alloy steel cap screws retaining a cast aluminum (356.0) diffuser assembly in a centrifugal refrigerant compressor failed in a brittle manner a short time after the system was placed in operation. Evidence obtained during the failure analysis indicated that the failures were the result of hydrogen embrittlement produced by galvanic corrosion and attendant evolution of hydrogen at the dissimilar junction, which was also the site of the highest tensile stress. Suggested measures for minimizing recurrences included use of lower-strength, galvanically-compatible fasteners and appropriately-applied and treated compatible coatings.

This article discusses the common causes of failures of springs, with illustrations. Design deficiencies, material defects, processing errors or deficiencies, and unusual operating conditions are the common causes of spring failures. In most cases, these causes result in failure by fatigue. The article describes the operating conditions of springs, common failure mechanisms, and presents an examination of the failures that occur in springs.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.