An aluminum bronze bushing that serves as a guide in a crimping machine began to fail after 50,000 cycles or approximately two weeks of operation. Until then, typical run times had been on the order of months. Although the bushings are replaceable and relatively inexpensive, the cost of downtime adds up quickly while operators troubleshoot and swap out worn components. Initially, the quality of the bushings came into question, but after a detailed analysis of the entire crimping mechanism, several other issues emerged that were not previously considered. As a result, the investigation provides information on not only better materials, but also design changes intended to reduce wear and increase service life.

An air system on a marine platform unexpectedly shut down due to the failure of a union nut, which led to an investigation to quantify the material limitations of bronze alloys in corrosive marine environments. The study focused on two alloys: Al-Si bronze, as used in the failed component, and Ni-Al bronze, which has a history of success in naval applications. Material samples were examined using chemical analysis, SEM imaging, and corrosion testing. Investigators also analyzed precracked tension specimens, exposing them to different conditions to quantify stress intensity thresholds for environmentally assisted cracking. Al-Si bronze was found to be susceptible to subcritical intergranular cracking in air and seawater, whereas Ni-Al bronze was unaffected. Both materials, however, are susceptible to cracking in the presence of ammonia, although the subcritical crack growth rate is two to three times higher in Ni-Al bronze. Based on the results of this work, the likelihood of subcritical cracking under various conditions can be reasonably estimated, which, in the case at hand, proved to be quite high.

Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.

The operator of an electric transit system purchased a large number of tin-plated copper connectors, putting some in service and others in reserve. Later, when some of the reserve connectors were inspected, the metal surfaces were covered with spots consisting of an ash-like powder and the plating material had separated from the substrate in many areas. Several connectors, including some that had been in service, were examined to determine what caused the change. The order stated that the connectors were to be coated with a layer of tin-bismuth (2% Bi) to guard against tin pest, a type of degradation that occurs at low temperatures. Based on the results of the investigation, which included SEM/EDS analysis, inductively coupled plasma spectroscopy, and x-ray diffraction, the metal surfaces contained less than 0.1% Bi and thus were not adequately protected against tin pest, which was confirmed as the failure mechanism in the investigation.

After about a year of uninterrupted service, one of the blow pipes on a blast furnace developed a bulge measuring 300 x 150 x 12 mm. The conical shaped section was removed from the furnace and examined to determine why it failed. The investigation consisted of visual inspection, chemical analysis, microstructural characterization, and mechanical property testing. The pipe was made from nonresulfurized carbon steel as specified and was lined with an alumina refractory. Visual inspection revealed cracks in the refractory lining, which corresponded with the location of the bulge. Microstructural and EDS analysis yielded evidence of overheating, revealing voids, scale, grain boundary oxidation, decarburization, and grain coarsening on the inner surface of the pipe, which also suggest the initiation of creep. Based on the information gathered during the investigation, the blow pipe was exposed to high temperatures when the liner cracked and subsequently bulged out due to creep.

A section from a stainless steel kitchen sink showed a round red stain on its surface after a short time in storage. Several of these sinks were stacked together and separated by felt pads while in storage, and the mating sink showed a nearly identical stain in the same area, while no stains were noted on any of the other sinks in the stack. The stain was located near one of the pads; however, no discoloration was noted at the pad location. EDS analysis showed the base metal to be austenitic stainless steel, such as type 304. FTIR analysis of the stain revealed carboxylic salts and salts of organic acids, in addition to hydroxyl functionality. The discoloration was caused by localized rusting of the sink from prolonged exposure to a chloride containing substance. The appearance suggests that the substance may actually have been a drop of perspiration (sweat) from a factory worker. Based on these findings, one of the recommendations was to use thicker pads between the sinks to allow any such liquids to dry before causing corrosion damage.

TiN coated back surgery wires were made of Ti-6Al-4V. The reported failure was the presence of pits located in the uncoated area of the wires. The uncoated area of the wire is where the wire is fixtured in the coating chamber during coating. Examination and analysis of the pits using SEM/EDX detection unit revealed significant peaks of B, O, Zr and Fe. Moreover, the shape of the pits was similar to an arc crater. The formation of pits in the wire was caused during coating due to microarcing. A contaminated fixture used during the coating most likely caused the microarcing.

U-shaped leaf springs, intended to serve as spacers between oil tank floats and the inner walls of the containers, broke while being fitted, or after a short time in use, in the bend of the U. The springs were made of tempered strip steel of type C 88 with 0.84 % C, bent at room temperature, and electroplated with cadmium for protection against corrosion. Each fracture showed seven or eight kidney-shaped cracks. At the origins of these cracks on the concave inner surface of the springs, crater-like depressions and beads of melted and resolidified material were found. Fracture of the springs was caused by stress cracks as a consequence of local hardening. The hardening caused by melting and resolidification, and therefore the cracks in the springs, was the result of a faulty procedure during cadmium electroplating.

The circumstances surrounding the in-service failure of a cast Ni-base superalloy (Alloy 713LC) second stage turbine blade and a cast and coated Co-base superalloy (MAR-M302) first stage air-cooled vane in two turbine engines used for marine application are described. An overview of a systematic approach, analyzing the nature of degeneration and failure of the failed components, utilizing conventional metallurgical techniques, is presented. The topographical features of the turbine blade fracture surface revealed a fatigue-induced crack growth pattern, where crack initiation had taken place in the blade trailing edge. An estimate of the crack-growth rate for the stage II fatigue fracture region coupled with the metallographic results helped to identify the final mode of the turbine blade failure. A detailed metallographic and fractographic examination of the air-cooled vane revealed that coating erosion in conjunction with severe hot-corrosion was responsible for crack initiation in the leading edge area.

Two acrylic-coated polymeric motorcycle components exhibited fisheye blemishes after painting. SEM and EDS results showed relatively high levels of sulfur and chlorine associated with the blemishes in both parts. This suggested some adherent residual substances, possibly in the form of processing fluids and/or cleaning agents, were left on the surface just prior to painting and resulted in the observed fisheye blemishes. One of the components also showed evidence of mechanical damage, in addition to detectable iron, which suggests that the part surface may have been damaged from contact with a ferrous material, such as a steel chip.

Extensive slipper/wobbler failures occurred in the integrated drive generators that incorporated TiN coated wobblers, during the production acceptance test. Similar coated wobblers had passed the application tests. The nature of the failure was extensive gouging of the wobbler surface with discoloration and coating removal. The substrate material was E52100 which was through-hardened to HRC 55-60. The slippers that were in contact with the coated wobbler surface were made of AISI 06 material. A synthetic oil was used as the hydraulic fluid in the application. The failure in the wobblers was caused by lack of temperature control during application which resulted in localized surface rehardening. It was established that there was a significant difference in the grade of the hydraulic fluid that was used in the two test programs. Use of superior grade of hydraulic fluid was recommended in this case for the production acceptance tests.

Investigation of alleged corrosion damage to hot-rolled steel during transit requires metallurgical, chemical, and corrosion knowledge. Familiarity with non-destructive techniques and sampling procedures is necessary. A complete record of shipment history is also required, including the purchasing specifications and observations and photographs taken during surveys enroute. A frequent conclusion of such investigations is that the alleged corrosion is of no significance or did not occur during the voyage.

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.

The surface of a hook did not possess the smooth and shiny zinc bloom surface normally observed on hot galvanized steel parts but was matte and rough. Large cracks were observed in the zinc layer. The hook was made of silicon-killed alloy steel 41Cr4. A silicon content of 0.27% was established analytically. Silicon accelerates the reaction between iron and zinc, which should have been taken into account in the present case by reducing the dip time or a small addition of aluminum (0.1 to 0.2%) to the galvanizing bath to retard the extremely rapid growth of the zinc layer and the strong alloy formation. Even in the case of steel parts with lower silicon contents the reaction between iron and zinc can continue until the pure zinc layer has been consumed entirely if the work piece is not cooled sufficiently after withdrawal.

This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.