Search Results for energy dispersive spectroscopy

This article focuses on the visual or macroscopic examination of damaged materials and interpretation of damage and fracture features. Analytical tools available for evaluations of corrosion and wear damage features include energy dispersive spectroscopy, electron probe microanalysis, Auger electron spectroscopy, secondary ion mass spectroscopy, and X-ray powder diffraction. The article discusses the analysis and interpretation of base material composition and microstructures. Preparation and examination of metallographic specimens in failure analysis are also discussed. The article concludes with a review of the evaluation of polymers and ceramic materials in failure analysis.

Gas turbines and other types of combustion turbomachinery are susceptible to hot corrosion at elevated temperatures. Two such cases resulting in the failure of a gas turbine component were investigated to learn more about the hot corrosion process and the underlying failure mechanisms. Each component was analyzed using optical and scanning electron microscopy, energy dispersive spectroscopy, mechanical testing, and nondestructive techniques. The results of the investigation provide insights on the influence of temperature, composition, and microstructure and the contributing effects of high-temperature oxidation on the hot corrosion process. Preventative measures are also discussed.

An investigation was conducted to better understand the time-dependent degradation of thermal barrier coated superalloy components in gas turbines. First-stage vanes are normally subjected to the highest gas velocities and temperatures during operation, and were thus the focus of the study. The samples that were analyzed had been operating at 1350 °C in a gas turbine at a combined-cycle generating plant. They were regenerated once, then used for different lengths of time. The investigation included chemical analysis, scanning electron microscopy, SEM/energy dispersive spectroscopy, and x-ray diffraction. It was shown that degradation is driven by chemical and mechanical differences, oxide growth, depletion, and recrystallization, the combined effect of which results in exfoliation, spallation, and mechanical thinning.

An investigation was conducted to determine why 16 out of 139 pipe bends cracked during hot induction bending. The pipe conformed to API 5L X65 PSL2 line pipe standards and measured 1016 mm (40 in.) in diam with a wall thickness of 18.5 mm. A metallurgical cross section was removed along a crack on the extrados to document the crack morphology using optical microscopy. In addition to cracking, golden-yellow streaks were visible at the extrados, and the composition was examined using scanning electron microscopy with energy dispersive spectroscopy. Based on the results, investigators concluded the pipe was contaminated with copper at the mill were it was produced.

Radial cracking occurred adjacent to 11 vanes in a 19-vane impeller operating in a chemical plant environment. The impeller vanes were fillet welded to both the disk and the cover Cracks were next to the fillet welds and near the cover outer diameter They generally did not extend to the outer diameter. The entire impeller surface was tested by the dry magnetic particle method. Visual and microstructural examinations revealed intergranular cracking. Energy-dispersive spectroscopy of corrosion products contained in the cracks disclosed the presence of chlorine and sulfur The failure was attributed to stress-corrosion cracking caused by a corrosive atmosphere.

A forged, cadmium-plated electroslag remelt (ESR) 4340 steel mixer pivot support of the rotor support assembly located on an Army attack helicopter was found to be broken in two pieces during an inspection. Visual inspection of the failed part revealed significant wear on surfaces that contacted the bushing and areas at the machined radius where the cadmium coating had been damaged, which allowed corrosion pitting to occur. Optical microscopy showed that the crack origin was located at the machined radius within a region that was severely pitted. Electron microscopy revealed that most of the fracture surface failed in an intergranular fashion. Energy dispersive spectroscopy determined that deposits of sand, corrosion and salts were found within the pits. The failure started by hydrogen charging as a result of corrosion, and was aggravated by the stress concentration effects of pitting at the radius and the high notch sensitivity of the material. The failure mechanism was hydrogen-assisted and was most likely a combination of stress-corrosion cracking and corrosion fatigue. Recommendations were to improve the inspection criteria of the component in service and the material used in fabrication.