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electrolytic polishing
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Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003532
EISBN: 978-1-62708-180-1
..., and electrolytic polishing. The article also describes the microstructure examination of various materials, with emphasis on failure analysis, and concludes with information on the examination of replicas with light microscopy. electrolytic polishing failure analysis field metallography fracture...
Abstract
This article provides a discussion on the metallographic techniques used for failure analysis, and on fracture examination in materials, with illustrations. It discusses various metallographic specimen preparation techniques, namely, sectioning, mounting, grinding, polishing, and electrolytic polishing. The article also describes the microstructure examination of various materials, with emphasis on failure analysis, and concludes with information on the examination of replicas with light microscopy.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001162
EISBN: 978-1-62708-220-4
... such as electrolytic and hand polishing and the vibration method resulted in poor edge and crack edge definition due to material thickness. Etching experiments involved a grain surface attack and hence produced a rather strong surface relief from which the grain boundary cracks could again not clearly...
Abstract
Some 99.90 pure tin tubes (0.15 mm thick) used for packaging a chemical compound cracked on bending and underwent brittle fracture prior to filling, while others remained ductile and showed no sign of failure. Examination showed that specimens prepared by mechanical methods such as electrolytic and hand polishing and the vibration method resulted in poor edge and crack edge definition due to material thickness. Etching experiments involved a grain surface attack and hence produced a rather strong surface relief from which the grain boundary cracks could again not clearly be differentiated. The sections were therefore examined unetched in polarized light. The microstructure of the cracked tubes was shown to have much smaller grains than the ductile and showed cracks from the surface down along the grain boundaries. Material hardness also differed between the unusable tubes and the ductile, and chemical analysis showed a higher level of aluminum in the brittle specimens. Failure obviously occurred due to the high material aluminum content that increased hardness which then caused embrittlement at the surface which led to cracks or fracture on bending. Since no explanation of how the aluminum entered the tin was available, no recommendations could be made.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001667
EISBN: 978-1-62708-235-8
... which included all of the consumables and the Di-Profiler. The equipment and consumble materials used in the on-site analysis are readily available in a well equipped metallurgical laboratory. No expensive dedicated field metallography equipment (such as a portable electrolytic polisher) was used...
Abstract
Nondestructive metallographic examination of materials frequently must be performed on-site when the component in question cannot be moved or destructively examined. Often, it is imperative that specific microstructural information (i.e., material type, heat treatment condition, homogeneity, etc.) be obtained either before initial use of a component, or before the use of a component can be safely resumed. In this paper, the use of standard metallurgical laboratory equipment, and the procedures required to conduct nondestructive on-site metallographic analyses of engineering materials, is presented. As an example, the materials and metallographic techniques employed in an actual on-site investigation of a gas tungsten-arc weldment joining two large diameter Ti-6Al-4V alloy cylinders are discussed in depth to illustrate what can be accomplished.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.pulp.c0089682
EISBN: 978-1-62708-230-3
.... Investigation (visual inspection, and micrographs of sections with electrolytic etching using 10 N KOH and then again after re-polishing and etching with Murakami's reagent) supported the conclusions that the casting never received a proper solution anneal. Recommendations included possible corrosion-screening...
Abstract
A neck fitting (cast equivalent of AISI type 317) exhibited extreme corrosion with large, deeply pitted areas. It had been in service in a sulfite digester at 140 deg C (285 deg F) and 689 kPa (100 psi). The liquor was calcium bisulfite, and chloride content was reported to be low. Investigation (visual inspection, and micrographs of sections with electrolytic etching using 10 N KOH and then again after re-polishing and etching with Murakami's reagent) supported the conclusions that the casting never received a proper solution anneal. Recommendations included possible corrosion-screening tests in accordance with ASTM A 262 to ensure adequate corrosion resistance.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006765
EISBN: 978-1-62708-295-2
..., and/or a brief vibratory polish (use the same cloths and abrasives as for step 4) may be needed to produce perfect publication-quality images. Electrolytic Polishing Electrolytic polishing can be used to prepare specimens with deformation-free surfaces. The technique offers reproducibility and speed...
Abstract
Metallographic examination is one of the most important procedures used by metallurgists in failure analysis. Typically, the light microscope (LM) is used to assess the nature of the material microstructure and its influence on the failure mechanism. Microstructural examination can be performed with the scanning electron microscope (SEM) over the same magnification range as the LM, but examination with the latter is more efficient. This article describes the major operations in the preparation of metallographic specimens, namely sectioning, mounting, grinding, polishing, and etching. The influence of microstructures on the failure of a material is discussed and examples of such work are given to illustrate the value of light microscopy. In addition, information on heat-treatment-related failures, fabrication-/machining-related failures, and service failures is provided, with examples created using light microscopy.
Image
in Flow-Induced Vibration Fatigue of Stainless Steel Impeller Blades in a Circulating Water Pump
> Handbook of Case Histories in Failure Analysis
Published: 01 December 1992
Fig. 6 Transgranular branching crack in blade prior to addition of weld buildup at blade-to-hub attachment. Titanium carbide/nitrate particles and their tracks from polishing are visible. Oxalic acid electrolytic etch. 50×.
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001178
EISBN: 978-1-62708-235-8
... Abstract Eight cylinderhead screws cracked after a short running time in motors. They were made of Fe-0.45C-1Cr steel, had rolled threads, were heat treated to 110 kg/sq mm tensile strength, and were electrolytically galvanized. All fractured at the root of the thread. The surfaces of fracture...
Abstract
Eight cylinderhead screws cracked after a short running time in motors. They were made of Fe-0.45C-1Cr steel, had rolled threads, were heat treated to 110 kg/sq mm tensile strength, and were electrolytically galvanized. All fractured at the root of the thread. The surfaces of fracture were fine-grained and had not spread by rubbing. Because the screws were electrolytically galvanized, failure resulted from “delayed fracture.” Experience has shown that this type of fracture is seen on production parts made of high-strength steels, which absorbed hydrogen during pickling or during a galvanic surface treatment. Such parts will rupture below the elastic limit during continuous stressing. This often occurs only after the expiration of a certain time period, and preferably at locations of stress concentrations such as changes in cross section or threads. As a rule, the hydrogen cannot be verified analytically because most of it escapes again after prolonged storage at room temperature or short heating at 100 to 200 deg C.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001825
EISBN: 978-1-62708-241-9
... in thermosetting epoxy and metallographically prepared. In addition, a transverse section of each tube section near the junction with the header was mounted and metallographically prepared. The prepared sections were examined as polished and after etching electrolytically in 10% oxalic acid. The examination...
Abstract
A type 304 stainless steel tube that failed in a boiler stack economizer was analyzed to determine the cause. The investigation consisted of visual, SEM/EDS, and metallographic analysis. Several degradation mechanisms appeared to be at work, including pitting corrosion, chloride stress corrosion cracking, and fatigue fracture. Investigators concluded that the primary failure mechanism was fatigue fracture, although either of the other mechanisms may have eventually caused the tube to fail in the absence of fatigue.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.auto.c9001704
EISBN: 978-1-62708-218-1
... the sample with a water-cooled abrasive saw and vacuum mounting it in epoxy. The cured sample was ground through 600 grit abrasive paper, rough-polished with 6 micron diamond, then final polished using a 0.3 micron aluminum oxide slurry. The sample was electrolytically etched in a 10 percent oxalic acid...
Abstract
Several type 304 stainless steel fire truck water tanks developed through-wall leaks after being in service for approximately two years. One representative tank underwent a comprehensive laboratory analysis, which included metallographic examinations and chemical analyses. The examinations revealed a classic case of microbiologically influenced corrosion (MIC), which preferentially attacked the heat affected zones of the tank welds, resulting in the leaks.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001049
EISBN: 978-1-62708-214-3
..., the presence of niobium-bearing carbide particles associated with the dendrites, and a crack following the interdendritic path. Figure 6 is a high-magnification view of this area and reveals microcracks adjacent to the carbide particles. Figure 7 , taken from a polished specimen, shows corrosion product...
Abstract
Routine inspections of a carbon steel wood pulp digester revealed a sharply increasing number of cracks in the overlay metal on the internal surface of the digester after 1 and 2 years of service. The weld overlay was composed of type 309 stainless steel on the top fourth of the digester and of a proprietary high-nickel material on the bottom three-fourths. Examination revealed three distinct modes of deterioration. General corrosion was linked to the use of unspecified overlay metal. Cracking resulted during installation from the use of a material susceptible to hot cracking. Deep corrosion fissures then developed at hot crack sites as a result of crevice corrosion. Use of the appropriate overlay material was recommended.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001034
EISBN: 978-1-62708-214-3
..., the inteiiors are polished to match the finish of the original steel, and great care is taken to avoid the formation of scratches and crevices that could serve as initation sites for corrosion. Often, however, the chemicals being hauled are not pure and contain contaminants that attack the stainless steel...
Abstract
The interior surface of a type 316L stainless steel trailer barrel used to haul various chemicals showed evidence of severe pitting after less than 1 year of service. Two sections were cut from the barrel and microscopically examined. Metallographic sections were also prepared at the weld areas and away from the weld zones. Terraced, near-surface pits with subsurface caverns and a high level of sulfur in the pit residue, both indicative of bacteria-induced corrosion, were found. No evidence of weld defects or defective material was present. Testing of the water used at the wash station and implementation of bacteria control measures (a special drying process after washing and use of a sanitizing rinse) were recommended.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001224
EISBN: 978-1-62708-232-7
... the sections after the usual etching with V2A-Beize which only attacks the austenitic matrix, were first etched electrolytically in a 1:10 dilution of saturated ammonia water at a terminal voltage of 1.5 V. This served to dissolve the chromium carbide and color it by means of a brown precipitate. Immediately...
Abstract
A recuperator for blast heating of a cupola furnace became unserviceable because of the brittle fracture of several finned tubes made of heat resistant cast steel containing 1.4C, 2.3Si and 28Cr. The service temperature was reported as 850 deg C. This led to the suspicion that the fracturing had something to do with the precipitation of sigma phase. Metallographic examination showed that the multiaxial stresses caused by sigma phase formation and the related embrittlement was the cause for the fracture of the recuperator. A steel of lower chromium content with no or little tendency for sigma phase formation would have had adequate corrosion resistance at the relatively low service temperature.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001059
EISBN: 978-1-62708-214-3
...) are used. The metal is finely polished with diamond paste down to a 0.25 µm (9.8 µin.) finish. When a scratch-free finish is attained, the material is etched electrolytically with 10% oxalic acid, and replicas of the surface are taken on 0.13 min (5 mil) acetate tape and transferred to glass slides...
Abstract
Field metallography and replication were performed on a type 316 stainless steel column in diglycol amine vacuum service to determine the cause of visible OD pitting on the column in several areas above the insulation support rings. The examination revealed transgranular stress-corrosion cracking beneath the pitted areas on the OD. The likely cause of the cracking was chloride stress corrosion, with chlorides deriving from the marine atmosphere and concentrating under the insulation around the support rings. A complete insulation evaluation, including repair or replacement, was recommended to prevent chloride buildup. Painting of the steel surface with an epoxy-phenolic or epoxy-coal tar was also suggested.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.rail.c9001175
EISBN: 978-1-62708-231-0
... of the boiler was polished and etched with Fry-solution, which revealed parallel striations formed due to the cold bending of the plate. The zones of slip were concentrated around the rivet holes. The cracks were formed here. The structure examination proved that the cracks had taken an exactly intercrystalline...
Abstract
A water tube boiler with two headers and 15.5 atm working pressure became leaky in the lower part due to the formation of cracks in the rivet-hole edges. The boiler plate of 20 mm thickness was a rimming steel with 0.05% C, traces of Si, 0.38% Mn, 0.027% P, 0.035% S, and 0.08% Cu. The mean value of the yield point was 24 (24) kg/sq mm, the tensile strength 39 (38) kg/sq mm, the elongation at fracture, d10, 26 (24)%, the necking at fracture 71 (66)% and notch impact value 11.5 (9.4) kgm/sq cm (the values in brackets are for the transverse direction). The specimen from inside surface of the boiler was polished and etched with Fry-solution, which revealed parallel striations formed due to the cold bending of the plate. The zones of slip were concentrated around the rivet holes. The cracks were formed here. The structure examination proved that the cracks had taken an exactly intercrystalline path, which is characteristic for caustic corrosion cracks. It was recommended that the internal stresses be removed through annealing or alternatively lye-resistant steel should be used.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001327
EISBN: 978-1-62708-215-0
... temperature and pulled apart in such a way that the fracture surface was undamaged. Multiple initiation sites were revealed. The cracks were typically half-moon shaped and covered with a tight, black adherent oxide film. The fracture surfaces were electrolytically cleaned and then visually examined. Two...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001696
EISBN: 978-1-62708-234-1
... to occur. The tubing was sectioned, mounted, and polished for metallographic examination. An austenitic microstructure was observed. Corrosion pitting and sulfide stringers (verified via EDX/S) were evident in the as-polished condition. The specimen was then electrolytically etched in a 10% oxalic acid...
Abstract
Piping and structural components used in space launch facilities such as NASA's Kennedy Space Center and the Air Force's Cape Canaveral Air Station face extreme operating conditions. Launch effluent and residue from solid rocket boosters react with moisture to form hydrochloric acid that settles on exposed surfaces as they are being subjected to severe mechanical loads imparted during lift-off. Failure analyses were performed on 304 stainless steel tubing that ruptured under such conditions, while carrying various gases, including nitrogen, oxygen, and breathing air. Hydrostatic testing indicated a burst strength of 13,500 psi for the intact sections of tubing. Scanning electron microscopy and metallographic examination revealed that the tubing failed due to corrosion pitting exacerbated by stress-corrosion cracking (SCC). The pitting originated on the outer surface of the tube and ranged from superficial to severe, with some pits extending through 75% of the tube's wall thickness. The SCC emanated from the pits and further reduced the service strength of the component until it could no longer sustain the operating pressure and final catastrophic fracture occurred. Corrosion-resistant coatings added after the investigation have proven effective in preventing subsequent such failures.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0048791
EISBN: 978-1-62708-234-1
... strength of 807 MPa (117 ksi), and the material should therefore meet the 517-MPa (75-ksi) tensile-strength requirement. A cross section was ground, polished, lightly etched in 10% oxalic acid, and examined optically. Intergranular cracks filled with oxide were observed to have depths up to about 8 mm...
Abstract
Linear indications on the outer surface of a cross in a piping system were revealed by dye-penetrant examination. The cross was specified to be SA403 type WP 304 stainless steel. The cross had been subjected to induction-heating stress improvement. The linear indications on the cross were located in wide bands running circumferentially below the cross-to-cap weld and above the cap-to-discharge-pipe weld. The material was found to conform to the requirements both in terms of hardness and strength. Intergranular cracks filled with oxide were observed on metallographic analysis of a sectioned and oxalic acid etched sample. The grain size was found to exceed the ASTM standard. No indications of sensitization were observed during testing with practice A of ASTM A 262. Definitive evidence of contaminants to support SCC as the failure mechanism was not disclosed during analysis. It was concluded that overheating or burning of the forging, which classically results in large grain size, intergranular fractures, and fine oxide particles dispersed throughout the grains was the possible reason for the failure.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001839
EISBN: 978-1-62708-241-9
... to observe the subsurface cracking and fissuring. The unetched, as-polished specimens were also concurrently examined under SEM at higher magnifications to garner more details about the defect. Metallographic specimens were eventually electrolytically etched in 10% oxalic acid solution at 6 V DC for 30 s...
Abstract
Several stainless steel coils cracked during a routine unwinding procedure, prompting an investigation to determine the cause. The analysis included optical and scanning electron microscopy, energy-dispersive x-ray spectrometry, and tensile testing. An examination of the fracture surfaces revealed a brittle intercrystalline mode of fracture with typical manifestations of clear grain facets. Branched and discrete stepwise microcracks were also found along with unusually high levels of residual hydrogen. Mechanical tests revealed a marked loss of tensile ductility in the defective steel with elongations barely approaching 8%, compared to 50% at the time of delivery weeks earlier. Based on the timing interval and the fact that failure occurred at operating stresses well below the yield point of the material, the failure is being attributed to hydrogen-induced damage. Potential sources of hydrogen are considered as are remedial measures for controlling hydrogen content in steels.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001489
EISBN: 978-1-62708-217-4
... loading; the comparison is being made with the polished surfaces and the tensile specimen fracture surfaces. The inclusions in the failed retaining ring were compared with the ones in a similar component obtained from a used engine. In the case of the latter, a large number of fine and elongated (Mn, Cr...
Abstract
The cause of the fatigue failure in the retaining ring of the compressor region of an aero-engine turbine was found to be the presence of a high concentration of nonmetallic inclusions. The results of chemical analysis were used to estimate the phases present. The most frequently observed inclusions were spinel solid solutions of the type MO middot; N2O3, where M = Fe, Mn, or Mg and N = Cr or Al. The detrimental inclusions were corundum, calcium aluminates, cristobalite, and silicates. The most detrimental phases were traced on the surfaces of the specimens fractured using impact loading; the comparison is being made with the polished surfaces and the tensile specimen fracture surfaces. The inclusions in the failed retaining ring were compared with the ones in a similar component obtained from a used engine. In the case of the latter, a large number of fine and elongated (Mn, Cr, Fe)S inclusions were present along with spinels. The nondeformable, rigid oxide particles are considered more undesirable than the sulfides as far as fatigue life of the component is concerned. It has been reported that the presence of sulfides may eliminate the stresses due to oxides.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006760
EISBN: 978-1-62708-295-2
... steel etched with electrolytic oxalic acid Erosion Turbulance and particulate in liquids can cause erosion, removing material with no corrosion product apparent. The surface exhibits bare metal. Erosion is usually classified as a type of wear ( Fig. 15 ). Fig. 15 (a) Erosion in copper...
Abstract
Visual examination, using the unaided eye or a low-power optical magnifier, is typically one of the first steps in a failure investigation. This article presents the guidelines for selecting samples for scanning electron microscope examination and optical metallography and for cleaning fracture surfaces. It discusses damage characterization of metals, covering various factors that influence the damage, namely stress, aggressive environment, temperature, and discontinuities.