The paper discusses the analysis of a coating defect on a high phosphorus electroless nickel (Ni-11 wt. % P) deposit plated on an aluminum alloy substrate. Preliminary investigations had indicated that the elongated defects were possibly caused by the entrapment of long fibers or particles during the plating. The possible sources of fibers were identified. The SEM/EDS analysis of fibers collected from the air duct filters correlated very well with the defect shape and the EDS profile collected from under the defect site. It appears that the fibers from air duct filters directly above the plating line were blown into the plating tank and getting co-deposited. The paper describes the step-by-step analysis of the defect that led to successful identification of the root cause of the defect.

The case study presented in this article details the failure investigation of an M50 alloy steel bearing used in a jet engine gearbox drive assembly. It discusses the investigative steps and analytic tools used to determine the root cause, highlighting the importance of continuous, thorough questioning by the investigating activity. The combined analyses demonstrated that the bearing failed by a single event overload as evidenced by bulk deformation and traces of foreign material on the rolling elements. The anomalous transferred metal found on the rolling elements subsequently led to the discovery of overlooked debris in an engine chip detector, and thus resulted in a review of several maintenance practices.

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.

The rear wall tube section of a boiler that had been in service for approximately 38 years was removed and examined. Visual examination of the tube revealed a small bulge with a through-wall crack. Metallography showed that the microstructure of the bulged area consisted of a few partially decarburized pearlite colonies in a ferrite matrix. The microstructure remote from the bulged area consisted of pearlite in a ferrite matrix. EDS analysis of internal deposits on the tube detected a major amount of iron, plus trace amounts of other elements. The evidence indicated that the bulge and crack in the tube resulted from hydrogen damage. Examination of the remaining water circuit boiler tubing using nondestructive techniques and elimination of any heavy deposit buildup was recommended.

This article describes some of the common elemental composition analysis methods and explains the concept of referee and economy test methods in failure analysis. It discusses different types of microchemical analyses, including backscattered electron imaging, energy-dispersive spectrometry, and wavelength-dispersive spectrometry. The article concludes with information on specimen handling.

Hardenability evaluation is typically applied to heat treatment process control, but can also augment standard metallurgical failure analysis techniques for steel components. A comprehensive understanding of steel hardenability is an essential complement to the skills of the metallurgical failure analyst. The empirical information supplied by hardenability analysis can provide additional processing and service insight to the investigator. The intent of this paper is to describe some applications of steel thermal response concepts in failure analysis, and several case studies are included to illustrate these applications.

A large number of electropolished copper parts showed evidence of discoloration (tinting) after electropolishing. Because these parts are used in a high-vacuum application, even trace amounts of organic materials would be problematic. Scanning electron microscopy of nondiscolored and discolored areas both showed trace amounts of residue in the form of adherent deposits. EDS, FTIR spectroscopy, XPS, and secondary ion mass spectroscopy (SIMS) analyses indicated that the discoloration to the copper components was due to the development of CuO at localized regions. It was recommended that process changes be made to completely remove residual processing fluids from the part surfaces before electropolishing. The use of more aggressive detergents was suggested, and it was recommended also that a filtering and recirculating system be considered for use in the cleaning and electropolishing tanks.

A stamped coin exhibited visible discolored areas, seen as a tan haze on the surface. The discoloration was considered merely cosmetic. The nonstained and stained regions were studied using SEM/EDS. Greater amounts of aluminum and magnesium were found in the stained area as compared with the nonstained region. Some carbon and oxygen were detected in both areas, which may be suggestive of organic substances. Fourier transform infrared spectroscopy (FTIR) revealed traces of hydrocarbons and ether/alcohol materials in the stained area, suggesting that the stain was associated with a cellulose or carbohydrates (sugars). These findings, along with the appearance, suggest that a sugar-containing substance, such as coffee or a soft drink, dried onto the surface of this coin and caused the observed discoloration.

Chemical analysis is a critical part of any failure investigation. With the right planning and proper analytical equipment, a myriad of information can be obtained from a sample. This article presents a high-level introduction to techniques often used for chemical analysis during failure analysis. It describes the general considerations for bulk and microscale chemical analysis in failure analysis, the most effective techniques to use for organic or inorganic materials, and examples of using these techniques. The article discusses the processes involved in the chemical analysis of nonmetallics. Advances in chemical analysis methods for failure analysis are also covered.

The causes of cracking of an as-drawn 90-10 cupronickel tube during mechanical working were investigated to determine the source of embrittlement. Embrittlement was sporadic, but when present was typically noted after the first process anneal. Microstructural and chemical analyses were performed on an embrittled section and on a section from a different lot that did not crack during forming. The failed section showed an intergranular fracture path. Examination of the fracture surfaces revealed the presence of tellurium at the grain boundaries. The source of the tellurium was thought to be contamination occurring in the casting process that became concentrated in the recycled skimmings. It was recommended that future material specifications for skimmings and for externally obtained scrap copper include a trace analysis for tellurium.

Several stainless steel bolts used on a Titan Space Launch Vehicle broke at the shank and failure was attributed to stress-corrosion cracking. But results could not be duplicated in the laboratory with salt-solution immersion tests until the real culprit was established: the secondary effect of galvanic coupling, hydrogen embrittlement.

An investigation was conducted to determine the cause of numerous cracks and other defects on the surface of a cast ASTM A743 grade CA-15 stainless steel main boiler feed pump impeller. The surface was examined using a stereomicroscope, and macrofractography was conducted on several cross sections removed from the impeller body. Areas that appeared to have the most severe surface damage were sectioned, fractured open, and examined using SEM. The chemistry of the impeller and an apparent repair weld were also analyzed. The examination indicated that the cracks were shrinkage voids from the original casting process. Surface repair welds had been used to fill in or cover over larger shrinkage cavities. It was recommended that more stringent visual and nondestructive examination criteria be established for the castings.

An air blower in an electric power plant failed unexpectedly when a roller bearing in the drive motor fractured along its outer ring. Both rings, as well as the 18 rolling elements, were made from GCr15 bearing steel. The bearing also included a machined brass (MA/C3) cage and was packed with molybdenum disulfide (MoS 2 ) lithium grease. Metallurgical structures and chemical compositions of the bearing’s matrix materials were inspected using a microscope and photoelectric direct reading spectrometer. SEM/EDS was used to examine the local morphology and composition of fracture and contact surfaces. Chemical and thermal properties of the bearing grease were also examined. The investigation revealed that the failure was caused by wear due to dry friction and impact, both of which worsened as a result of high-temperature degradation of the bearing grease. Fatigue cracks initiated in the corners of the outer ring and grew large enough for a fracture to occur.

Cracks, with no other damage, were observed in a niobium alloy (Nb-106) part when it was pulled from several months of protective storage for assembly into a rocket nozzle. SEM views showed the cracks to be intergranular, with contaminant particles on a large number of the grain facets. EDX analysis showed they consisted of niobium and fluorine. Plastic replicas, prepared by standard TEM techniques, were analyzed with selected-area electron diffraction, showing a pattern match for niobium tetrafluoride. Auger analyses showed electron spectra containing peaks representing carbon, oxygen, nitrogen, fluorine, and chlorine. Investigation into the processing history of the part showed the tenacious oxide film formed by the affinity of niobium for oxygen - even when heat treated in a vacuum – was removed with a combination of strong acids: nitric, hydrochloric, hydrofluoric, and lactic, resulting in the contaminants found on the surface. Thus, residues of the cleaning acid on the part had caused SCC during storage, with the tensile stresses necessary to generate SCC assumed to have been residual stresses from the heat treatment. Recommendation was made that more stringent cleaning procedures to remove any trace of the cleaning acids be used.

A locked coil track rope (LCTR) is essentially composed of wires (round and rail-shaped) laid helically in different layers. These wire ropes are sometimes used in conveyors carrying empty and loaded buckets in mining areas. During service, such wire ropes may fail prematurely due to disintegration/failure of individual groups of wires. To understand the genesis of LCTR wire failures, a detailed metallurgical investigation of failed rope wires was made and included visual examination, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Two types of failed wires were investigated; one is from a 40 mm diameter locked coil track rope and the other from a 53 mm locked coil track rope. Optical microscopy of failed round wires in the 53 mm diameter rope clearly revealed fully decarburized layers at the surface and a few grain-boundary cracks. From the location of the failure, it was clear that apart from static tensile loads, the wire ropes had been subjected to bending and unbending loads near the saddle, as fully loaded or empty buckets traveled access the conveyor. The SEM studies confirmed that the fracture had been caused by initiation of fatigue cracks in the decarburized zone under conditions of repeated bending and unbending stresses superimposed on the static tensile load.

Heating elements, consisting of strips, 40 mm x 2 mm, of the widely used 80Ni-20Cr resistance heating alloy, and designed to withstand a temperature of 1175 deg C, were rendered unusable by scaling after a few months service in a through-type annealing furnace, Although the temperature supposedly did not exceed 1050 deg C. Structural observations indicated a special case of internal oxidation. The required conditions for this were apparently provided by the moist hydrogen atmosphere of the annealing furnace, in which the chromium was oxidized, while the oxides of iron and nickel were reduced. Even the carbon suffered incomplete combustion and was enriched in the core. Thus, no protective layer could form or be maintained. The intergranular advancement of the oxidation may have been favored by the precipitation of chromium-rich carbides on the austenite grain boundaries. This form of internal oxidation is, in the case of Ni-Cr alloys, known as green rot. Alloys containing iron should be more resistant. As a preventive measure it was recommended to reduce the operating temperature of the strip sufficiently to allow the use of Fe-Ni-Cr alloys.

A tie rod, nut, and bellows from a failed 610 mm (24 in.) diam tied universal expansion joint that carried tail gases consisting of N 2 + O 2 with slight traces of nitrogen oxides and water were examined. The materials were SA 193-B7 (AISI 4140), SA 194–214, and Incoloy 800H, respectively. Visual examination of the bellows revealed cracks in heavily cold-worked areas (both inside and outside) and considerable corrosion. SEM analysis showed a classical intergranular failure pattern with microcracking. The threaded tie rod microstructure contained spheroidized carbide that was more pronounced at the tie rod end of the failure. Energy-dispersive X-ray analysis of fracture surfaces from the bellows showed the presence of chlorine and sulfur. Failure of the bellows was attributed to stress-corrosion cracking, with chlorine and sulfur being the corroding agents. The rod damage was the result of failure of the bellows, which allowed escaping hot gases to impinge on the tie rods and heat them to approximately 595 deg C (1100 deg F). It was recommended that the insulation be analyzed to determine the origin of the chlorine and sulfur and that it be replaced if necessary.

During the preproduction stages of forging, an initial batch of 50 mm (2 in.) diam Al-4Cu alloy (L77) extruded bar stock material was found to be cracking randomly. Failure analysis was conducted to determine the metallurgical factors underlying the phenomenon. Microexamination of sections across the defects revealed intergranular cracks tracing a path of round, segregated particles and oxide film discontinuities. The segregated particles were rich in copper It was concluded that the cracking was the result of segregations occurring in poor-quality raw material. The source of segregation was suspected to be the use of improperly made master alloys. Use of improved melting techniques and proper master alloys was recommended.

An investigation of the impeller and deposit samples from a centrifugal compressor revealed that an aluminum IR-12 refrigerant reaction had occurred, causing extensive damage to the second-stage impeller and contaminating the internal compressor components. The spherical surface morphology of the impeller fragments suggested that the aluminum had melted and resolidified. The deposits were similar in composition and were identified by XRD as consisting primarily of aluminum trifluoride. In addition, EDS analysis detected major amounts of chlorine and iron. Results of a combustion test indicated that the compressor deposit was comprised of a 9. 8 wt% carbon and that the condenser deposit contained 8.7 wt% carbon. It was concluded that the primary cause of failure was the rubbing of the impeller against the casting and that a self-sustaining Freon fire had occurred in the failed compressor

Two 20 MW turbines suffered damage to second-stage blades prematurely. The alloy was determined to be a precipitation-hardening nickel-base superalloy comparable to Udimet 500, Udimet 710, or Rene 77. Typical protective coatings were not found. Test results further showed that the fuel used was not adequate to guarantee the operating life of the blades due to excess sulfur trioxide, carbon, and sodium in the combustion gases, which caused pitting. A molten salt environmental cracking mechanism was also a factor and was enhanced by the working stresses and by the presence of silicon, vanadium, lead, and zinc. A change of fuel was recommended.