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.

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.

The presence of subsurface cracks in a longitudinal weld seam of an AISI type 316 stainless steel heat-exchanger shell was revealed by radiographic testing. Numerous intergranular cracks associated with the root pass of the weld, which had propagated both parallel and normal to the weld seam, were revealed by metallographic examination (hot shortness). It was indicated by energy-dispersive spectroscopy that type 316 electrode was not used for the root pass and instead a nickel-copper alloy electrode was employed. It was thus concluded that cracking was caused due to the use of an incorrect electrode for the root pass as these electrodes are crack sensitive if overheated. The weld seam was completely ground out and replaced with the correct electrode material as a corrective measure.

A kiln, 7.6 m (25 ft) long with a 1 m (3 ft) internal diameter and a 6.3 mm (0.25 in.) wall thickness, is used to regenerate spent charcoal returned by water utilities. This charcoal contains up to 0.57% S and 2.04% Cl. The kiln is made of Inconel 601 (N06601) welded using Inconel 617 (N06617) as a filler alloy. Wet charcoal is fed in at one end of the kiln and travels while being tumbled within the inclined rotating vessel. Temperatures range from 480 deg C (900 deg F) (Zone 1) to 900 deg C (1650 deg F) (Zones 2 and 3). Steam is introduced at the discharge end at 95 g/s (750 lb/h), 34 to 69 kPa (5 to 10 psi), and 125 deg C (260 deg F). The kiln developed perforations within eight months of operation. Investigation (visual inspection, metallurgical analysis, energy-dispersive spectroscopy, and 44X micrographs) supported the conclusion that the sulfur and chlorine in the charcoal attacked the Inconel 601, forming various sulfides and chlorides. Recommendations included on-site testing, and installation of test coupons of various alloys before fabricating another kiln. The suggested alloys were RA85H, 800HT, HR-120, Haynes 556, and HR-160.

The US Army Research Laboratory performed a failure investigation on a broken main landing gear mount from an AH-64 Apache attack helicopter. A component had failed in flight, and initially prevented the helicopter from safely landing. In order to avoid a catastrophe, the pilot had to perform a low hover maneuver to the maintenance facility, where ground crews assembled concrete blocks at the appropriate height to allow the aircraft to safely touch down. The failed part was fabricated from maraging 300 grade steel (2,068 MPa [300 ksi] ultimate tensile strength), and was subjected to visual inspection/light optical microscopy, metallography, electron microscopy, energy dispersive spectroscopy, chemical analysis, and mechanical testing. It was observed that the vacuum cadmium coating adjacent to the fracture plane had worn off and corroded in service, thus allowing pitting corrosion to occur. The failure was hydrogen-assisted and was attributed to stress corrosion cracking (SCC) and/or corrosion fatigue (CF). Contributing to the failure was the fact that the material grain size was approximately double the required size, most likely caused from higher than nominal temperatures during thermal treatment. These large grains offered less resistance to fatigue and SCC. In addition, evidence of titanium-carbo-nitrides was detected at the grain boundaries of this material that was prohibited according to the governing specification. This phase is formed at higher thermal treatment temperatures (consistent with the large grains) and tends to embrittle the alloy. It is possible that this phase may have contributed to the intergranular attack. Recommendations were offered with respect to the use of a dry film lubricant over the cadmium coated region, and the possibility of choosing an alternative material with a lower notch sensitivity. In addition, the temperature at which this alloy is treated must be monitored to prevent coarse grain growth. As a result of this investigation and in an effort to eliminate future failures, ARL assisted in developing a cadmium brush plating procedure, and qualified two Army maintenance facilities for field repair of these components.