A missile detached from a Navy fighter jet during a routine landing on an aircraft carrier deck because of a faulty missile launcher detent spring. Visual inspection of Inconel 718 detent spring assembly revealed that four of the nine spring leafs comprising the assembly were plastically deformed while two of the deformed leafs did not meet minimal hardness or tensile requirements. Liquid penetrant testing revealed no cracks or other surface discontinuities on the leaf springs. Material sectioned from the soft spring leafs was heat-treated according to specifications in the laboratory. The resultant increase in mechanical properties of the re-heat-treated material indicated that the original heat treatment was not performed correctly. The failure was attributed to improper heat treatment. Recommendations focused on more stringent quality control of the heat-treat operations.

A valve stem made of 17-4 PH (AISI type 630) stainless steel, which was used for operating a gate valve in a steam power plant, failed after approximately four months of service, during which it had been exposed to high-purity water at approximately 175 deg C (350 deg F) and 11 MPa (1600 psi). The valve stem was reported to have been solution heat treated at 1040 +/-14 deg C (1900 +/-25 deg F) for 30 min and either air quenched or oil quenched to room temperature. The stem was then reportedly aged at 550 to 595 deg C (1025 to 1100 deg F) for four hours. Investigation (visual inspection, 0.7x/50x images, hardness testing, reheat treatment, and metallographic examination) supported the conclusion that failure was by progressive SCC that originated at a stress concentration. Also, the solution heat treatment had been either omitted or performed at too high of a temperature, and the aging treatment had been at too low of a temperature. Recommendations included the following heat treatments: after forging, solution heat treat at 1040 deg C (1900 deg F) for one hour, then oil quench; to avoid susceptibility to SCC, age at 595 deg C (1100 deg F) for four hours, then air cool.

An air bottle, machined from a solid block of aluminum alloy 2219-T852, displayed liquid-penetrant crack indications after assembly welding. The air bottle was machined to rough shape, a 3.8 mm (0.15 in.) wall thickness cylindrical cup with a 19 mm (3/4 in.) wall thickness integral boss on one side. After annealing, hot spinning, annealing a second time, and tack welding a port fitting, the assembly was torch preheated to 120 to 150 deg C (250 to 300 deg F). The port fitting was then welded in place. Final full heat treatment to the T62 temper was followed by machining, testing, and inspection. The crack indications were found only on one side of the boss and on the lower portion of the hot-spun dome region. The metallographic specimens revealed triangular voids and severe intergranular cracks. The cracks displayed the glossy surfaces typical of melted and resolidified material. The localized cracks in the air bottle were from grain-boundary eutectic melting caused by local torch overheating used in preparation for assembly welding of a port fitting. A change in design was scheduled to semiautomatic welding without the use of preheating for the joining of the port fitting for the dome opening.

A forged aluminum alloy 2014-T6 catapult-hook attachment fitting (anodized by the chromic acid process to protect it from corrosion) from a naval aircraft broke in service. Spectrographic analysis, visual examination, microscopic examination, and tensile analysis showed minute cracks on the inside surface of a bearing hole, and small areas of pitting corrosion were visible on the exterior surface of the fitting. The analysis also revealed a small number of rosettes, suggestive of eutectic melting, in an otherwise normal structure. These examinations and analyses support the conclusion that the presence of chromic acid stain on the fracture surface proved that the forging had cracked before anodizing. This suggest that the crack initiated during straightening, either after machining or after heat treatment. The structure and composition of the alloy appear to have been acceptable. Ductility was acceptable so rosettes found in the microstructure are believed to have been nondamaging. Had they contributed to the failure, the ductility would have been very low. The recommendations included inspection for cracks and revising the manufacturing process to include a fluorescent liquid-penetrant inspection before anodizing, because chromic acid destroys the penetrant. This inspection would reduce the possibility of cracked parts being used in service.

A type 321 stainless steel (AMS 5570) pressure-tube assembly that contained a brazed reinforcing liner leaked during a pressure test. Fluorescent liquid-penetrant inspection revealed a circumferential crack extended approximately 180 deg around the tube parallel to the fillet of the brazed joint. The presence of multiple origin cracks was indicated on the inside surface of a fractured portion of the crack surface. The cracks had originated adjacent to the braze joining the tube and the reinforcing liner and propagated through the wall to the outer surface. The residues on the inner surface of the tube were identified as fluorides from the brazing flux by chemical analysis. The nature of the crack, potential for corrosion due to residual fluorides and residual swaging stress in the tube prior to brazing, confirmed that failure of the tube end was due to stress-corrosion cracking. Stress relief treatment of tube before brazing and immediate cleaning of brazing residual fluorides was recommended to avoid failure.

This article describes the six fundamental factors that decide a tool's performance. These are mechanical design, grade of tool steel, machining procedure, heat treatment, grinding, and handling. A deficiency in any one of the factors can lead to a tool and die failure. The article presents a seven-step procedure to be followed when looking for the reason for a failure. A review of the results of the seven-point investigation may lead directly to the source of failure or narrow the field of investigation to permit the use of special tests.

A bearing cup in a drive shaft assembly on an automobile was found to have failed. A detailed analysis was conducted using the QC story approach, which begins by proposing several possible failure scenarios then following them to determine the main root cause. A number of alternative solutions were identified and then validated based on chemical analysis, endurance and hardness tests, and microstructural examination. The investigation revealed that carbonitriding can effectively eliminate the type of failure encountered because it prevents through hardening of the bearing cup assembly.

This article describes the characteristics of tools and dies and the causes of their failures. It discusses the failure mechanisms in tool and die materials that are important to nearly all manufacturing processes, but is primarily devoted to failures of tool steels used in cold-working and hot-working applications. It reviews problems introduced during mechanical design, materials selection, machining, heat treating, finish grinding, and tool and die operation. The brittle fracture of rehardened high-speed steels is also considered. Finally, failures due to seams or laps, unconsolidated interiors, and carbide segregation and poor carbide morphology are reviewed with illustrations.

This article discusses failure mechanisms in tool and die materials that are very important to nearly all manufacturing processes. It is primarily devoted to failures of tool steels used in cold working and hot working applications. The processes involved in the analysis of tool and die failures are also covered. In addition, the article focuses on a number of factors that are responsible for tool and die failures, including mechanical design, grade selection, steel quality, machining processes, heat treatment operation, and tool and die setup.

An AISI D2 tool steel insert from a forming die used in the manufacture of automotive components failed prematurely during production. Results of various analyses and simulation tests indicated fatigue failure resulting from improper heat treatment. The fatigue fracture originated because of a highly stressed condition produced by a sharp corner combined with low toughness from ineffective tempering. It was recommended that 25 other inserts that belonged to the same die be double tempered.

Metal-induced embrittlement is a phenomenon in which the ductility or fracture stress of a solid metal is reduced by surface contact with another metal in either liquid or solid form. This article summarizes the characteristics of solid metal induced embrittlement (SMIE) and liquid metal induced embrittlement (LMIE). It describes the unique features that assist in arriving at a clear conclusion whether SMIE or LMIE is the most probable cause of the problem. The article briefly reviews some commercial alloy systems where LMIE or SMIE has been documented. It also provides some examples of cracking due to these phenomena, either in manufacturing or in service.

Metal-induced embrittlement is a phenomenon in which the ductility or the fracture stress of a solid metal is reduced by surface contact with another metal in either the liquid or solid form. This article summarizes some of the characteristics of liquid-metal- and solid-metal-induced embrittlement. This phenomenon shares many of these characteristics with other modes of environmentally induced cracking, such as hydrogen embrittlement and stress-corrosion cracking. The discussion covers the occurrence, failure analysis, and service failures of the embrittlement. The article also briefly reviews some commercial alloy systems in which liquid-metal-induced embrittlement or solid-metal-induced embrittlement has been documented and describes some examples of cracking due to these phenomena, either in manufacturing or in service.

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

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.

Erosion of solid surfaces can be brought about solely by liquids in two ways: from damage induced by formation and subsequent collapse of voids or cavities within the liquid, and from high-velocity impacts between a solid surface and liquid droplets. The former process is called cavitation erosion and the latter is liquid-droplet erosion. This article emphasizes on manifestations of damage and ways to minimize or repair these types of liquid impact damage, with illustrations.

Identification of alloys using quantitative chemical analysis is an essential step during a metallurgical failure analysis process. There are several methods available for quantitative analysis of metal alloys, and the analyst should carefully approach selection of the method used. The choice of appropriate analytical techniques is determined by the specific chemical information required, the condition of the sample, and any limitations imposed by interested parties. This article discusses some of the commonly used quantitative chemical analysis techniques for metals. The discussion covers the operating principles, applications, advantages, and disadvantages of optical emission spectroscopy (OES), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray spectroscopy, and ion chromatography (IC). In addition, information on combustion analysis and inert gas fusion analysis is provided.

This article introduces some of the general sources of heat treating problems with particular emphasis on problems caused by the actual heat treating process and the significant thermal and transformation stresses within a heat treated part. It addresses the design and material factors that cause a part to fail during heat treatment. The article discusses the problems associated with heating and furnaces, quenching media, quenching stresses, hardenability, tempering, carburizing, carbonitriding, and nitriding as well as potential stainless steel problems and problems associated with nonferrous heat treatments. The processes involved in cold working of certain ferrous and nonferrous alloys are also covered.

A 1-in. diam pump spindle fractured within the length covered by the boss of the impeller which was attached to the spindle by means of an axial screw. The pump had been in use in a chemical plant handling mixtures of organic liquids and dilute sulfuric acid having a pH value of 2 to 4 at temperatures of 80 to 90 deg C (176 to 194 deg F). The fracture was unusual in that it was of a fibrous nature, the fibers-which were orientated radially-were readily detachable. The surface of the spindle adjacent to the fracture had an etched appearance and the mode of cracking in this region suggested that failure resulted from an intergranular attack. Subsequent microscope examination confirmed the generally intergranular mode of failure. A macro-etched section near the fracture revealed a radial arrangement of columnar crystals, indicating that the spindle was a cast and not a wrought product as had been presumed. Spectroscope examination showed this particular composition (Fe-23Cr-18Ni-1.8Mo-1.2Si) did not conform to a standard specification and is apparently a proprietary alloy. It was evident that the particular mode of failure was related to the inherent structure of the material.

One-quarter inch diameter 304 stainless steel cooling tower hanger rods failed by chloride-induced stress-corrosion cracking (SCC). The rods were located in an area of the cooling tower where the air contains drop lets of water below the mist eliminators and above the flow of water The most extensive cracking was observed in the rod nuts and in the portions of the rod which were covered by the nuts. Cracking was transgranular with extensive branching, and some corrosion occurred along the crack paths. The clamping force from the nuts used on both sides of the supported member and residual stresses from thread rolling likely contributed to the stresses for the cracking mechanism, along with the stresses induced by the supported load. The external surfaces of the hanger rods were reportedly exposed to a chloride-containing atmosphere, likely due to the biocide. Type 304 stainless steel is not a suitable material for this application, and materials that resist SCC, such as Inconel, should be considered.

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.