Microstructural and chemical surface and rim zone changes of ferrite‐perlite 42CrMo4 steel after electrochemical machining

Electrochemical machining is based on the anodic dissolution of most metals and generates high quality polished surfaces. However, ferrite-perlite 42CrMo4 steel reveals local optical changes at surface after electrochemical finishing, such as a widely variable finish from shiny (reflective) to rough (dark) surfaces even one processing step. The different areas (AISI 4140) are studied by electron microscopy techniques, x-ray diffraction photoelectron spectroscopy gain information about chemistry reaction layers residual stresses rim zone. results show that zone for 50 nm–100 nm thick contain oxygen. Selected area formation iron(II/III) oxide (Fe3O4) confirms mixed iron (Fe3-xO4) with variation oxidation state both near-surface zones. Furthermore, reflective reveal homogeneous ferrite cementite lamellae whereas preferred an inhomogeneous within X-ray measurements do not any introduced in Die elektrochemische Bearbeitung basiert auf der anodischen Auflösung meisten Metalle und erzeugt polierte Oberflächen mit einer hohen Oberflächenqualität. Nichtsdestotrotz weist ferritisch perlitische Stahl eine deutlich unterschiedliche Oberflächenqualität von optisch glänzenden bis zu dunklen, schwarzen Oberfläche auf. unterschiedlichen werden verschiedenen elektronenmikroskopischen Methoden, Röntgenbeugung Röntgenphotonenspektroskopie untersucht, um Informationen über die lokale chemische Zusammensetzung Reaktionsschichten Eigenspannungen erhalten. Ergebnisse zeigen, dass Randschicht ca. dick ist Sauerstoff enthält. Feinbereichsbeugung zeigt Bildung Eisen(II/III)-Oxid, bestätigt verschiedener Eisenoxide Variation des Oxidationszustandes für beide oberflächennahen Randschichten. glänzende homogene Ferrit- Zementitlamellen, wohingegen dunkle bevorzugte Zementitlamellen inhomogene Ferrit aufweist. keine, durch den Prozess eingebrachte Randschicht. allows enables function-oriented manufacturing only used generating profiles cannot be gained other process, but also achieving without undesirable tensile stresses. Investigations ferrite-pearlite showed optically formed machining, varying between dark (rough) appearance already step 1. A can generated micro-smoothing which suppression influence defects crystal orientation depends passivation behavior chemical microstructural composition material 2, 3. Mass transport dissolved metal ions responsible crucial factor change etching brightening 2. Since concentration increases along length gap during finishes occur. Alloying elements like chromium have process resulting High amounts chromium, present stainless steels, known generate protective layer, called prohibits or least reduces external electric field. For use nitrate electrolytes, these considered consist two distinct regions steels: inner layer rich (mainly chromium(III) oxide) outer, more hydrated richer 4. Passivation maintained due reduced diffusivity through layer. Another model states oxides (iron(II/III) iron(III) outer layer) 100Cr6 5. sodium strongly attached allow trans-passive iron(+III) electrode potentials > 1.8 V. Current studies martensitic solution revealed significant dependence current density stoichiometry substitution molybdenum 6. If gets partly ruptured locally densities erosion carbides, pits may form. properties highly depend conditions well products. investigation determination zones challenging their small thickness several tens hundreds nanometers subject this study. resolution imaging technologies work investigate microstructure variations machining. In following, characterization methods presented. sample matrix was pre-processed order remove heat treatment deformation former processes, were desired geometry. Then, actual electro-chemical applied. performed PT Smart 1500 EMAG. An applied potential difference 19 V, feed 1 mm/min, electrolyte pressure 106 MPa, initial working 0.3 mm sinking depth 0.5 parameters. consisted 21 wt. % solution. conducted using flow fixture, directly mechanical machine axis, Figure fixture provides consistent flushing gap, stability. Therefore, stationary assumed process. Flow Fließvorrichtung bei elektrochemischen Bearbeitung. scanning analyses energy dispersive spectroscopy, JEOL JSM-7000F microscope equipped Octane Plus SSD detector EDAX-TSL used. acceleration voltage images 15 kV. transmission Tecnai F20 FEI Veleta camera, analog camera system GIF Gatan. 200 Additionally, Libra FE Zeiss gaining elemental maps filtering. Samples prepared dual beam FIB (focused ion beam) Strata 400 S. carbon platinum deposited protection before preparation. Energy filtered qualitative way distribution FIB-lamella. When electrons pass lamella some knock out atom shells material. Depending element, activation energies necessary out. loose part energy. magnetic filter separate losses form electrons. acquired three-window-method, Table S1 (supporting information). corrected so they give no quantitative occurring elements. Residual measured General Electric Inspection Technologies analytical MZ VI E line photron-X PSD-50L. measurement theta-2theta mode evaluation (211) peak (ferrite/ martensite) sin2psi-method tilt angle −45° +45° 11 steps. diameter aperture 2 depth, where came from, 10 μm. main σ parallel (0°) perpendicular (90°) direction. full width half maximum peaks crystallite size dislocation density. smaller grains higher dislocation/ defect greater maximum. carried Kratos Axis Supra instrument (Kratos Analytical Ltd.). monochromatic aluminum K source (h ⋅ ν = 1486.6 eV) Wide scans 20 eV 0.25 achieve composition. addition, spectra oxygen s, p, 3 d, nitrogen s obtained 0.1 attain binding state. deconvolution quantification ESCApe software charge correction against adventitious carbon-carbon contamination component 284.8 executed all spectra. Shirley type backgrounds Peak fitting Gauss-Lorentz (30/70) shapes exception metallic component, required asymmetric shapes. Depth appearances, (reflective), recorded iteratively sputtering 500 argon 240 subsequent survey spectrum. One advantages Additional parameters, fluid dynamics, selective passive homogeneity low alloyed steels result modifications. Variations machined into areas, following sections, examined. Picture matrix. Part surface, started, appears (rough). red points mark position measurements. Fotographie elektrochemisch bearbeiteten Probe einem ferritisch-perlitischen Grundgefüge. Der Teil Oberfläche, wo Spülung dem Elektrolyten begonnen hat, glänzend, andere erscheint dunkel. roten Punkte markieren Position Röntgenbeugungsmessung. very modified 100 less thickness. investigations cross section useless because too analyzed section. it has close partially salts washed preparation So, secondary topography, – cut focused sections determine modifications almost smooth final polishing microscopic analyses, roughness looks pitting corrosion, Cementite clearly visible there preferable phase compared reported 7. exhibits slight roughness, examined (see further sections). positions marked yellow chromium. silicon stems detector. Molybdenum Kα could detected excitation Lα seen feature quite shows pronounced deposits. still visible, fissured pits. additional oxygen, calcium might topography. Refreshment hindered lamellae, leading enhanced salt deposits carbides a) Secondary image b) c) spectrum d) surface. marks measurement. Sekundärelektronenbild dunklen energiedispersives Röntgenspektrum Oberfläche. gelben Kreuze energiedispersiven Röntgenspektrometriemessung. Modified supposed usually film μm wolfram placed protect gallium beam. than (heavy metal) prevent analysis Although seems, if thin around both, Figures 3–5. huge differences topography observed therefore confirmed microscopy. It related localized dependent removal, single phases microstructure. Specifically, considered. indicate associated lamellae. On seem sort bending contrast tilting angles equally ferrite, 5a darker lamellae). preferably removed nm–300 deep channels matrix, 5b. Bright field White vacuum holes lamella, homogeneously grey top film. Hellfeld-Bild Lamelle, geschnitten aus Weiße Bereiche entsprechen Vakuum bzw. Löchern graue im oberen Bildes sind aufgebrachte Kohlenstoffschutzfilm. resolution. höherer Auflösung. filtering especially useful light carbon, map, manganese map (manganese shown here), 6b, c, d. surface-near contains 6e. bright (marked arrow) suggest increase (nitrogen here). Thickness fringes contours map. As (and molybdenum) turn up same those contours, artifact preservation elastic scattering contrast. This happens, drifts slightly its therefore, position. content ellipse). Lamella surface: image, element brighter contrast: e) f) displaying t/λ-value; black vacuum, blue means (t/λ < 1), green/ (1 t/λ 2.1). & white print: color lamella. Lamelle Oberfläche: Hellfeld-Bild; Eine höhere Elementkonzentration Energie gefilterten Bildern heller: Kohlenstoff-Map, Chrom-Map, Eisen-Map, Sauerstoff-Map, Schichtdicken-Map, t/λ-Wert angibt; schwarz entspricht Vakuum, blau bedeutet dünne grün/ rot dicke Für weiß Print: dunkel hell Lamelle. Just increased 6, 7e, f. Stickstoff-Map. Due nm, smallest selected chosen zone, 8, 9. Otherwise, spots would strong ones patterns indexed reflexes added. evaluated lattice plane distances originate eight (four four surface), S2, supporting information. reference values taken ICSD data base Collcodes 52258 (α-iron), 99016 (cementite), 239322 (iron hydroxide), 15840 (iron(III) oxide), 43001 8 167268 (chromium(III) oxide). aperture, corresponding pattern, pattern; remaining big belong α-iron eingezeichneter Feinbereichsbeugungsblende, zugehöriges Beugungsbild, indiziertes übrigen großen Spots gehören zum α-Eisen Identification complicated fact above 2.00 Å uncertainty reciprocal space; deviation few pixels calculated distances. below 1.00 Å, much accurate amount possible lot, structures carbides. So kind structure going fit spots. reliable distance whereat should 0.01 Å. According images, unambiguously oxides. hydroxide 1.5 better. There another possibility: mainly located preferentially build anode well. Chromium anodically dissolve chromate anion dichromate causing acidic environment obvious although match values, 10, S2. hit mix oxide. Of course, biggest challenge identification pattern. Unless distances, impossible diffraction. fortuitously turned axis determined unambiguously, 8. Iron(II/III) fitted spectrum; green correspond cementite, Copper originates grid, Carbon been vertically offset distinguish profiles. zugehörige energiedispersive Röntgenspektren; grünen Flächen blauen Eisen-Matrix. anderen veränderten Kupfer stammt vom Kupfer-Grid, Gallium wurde während Präparation Gallium-Ionen-Strahl implementiert. Kohlenstoff kann aufgebrachten Kohlenstofffilm stammen. Spektren wurden vertikal verschoben Profile besser unterscheiden können. MPa error bars comparatively large since does cause stresses, 11a, 12b. 0 calibration existence (ferrite cementite) long treatments slow cooling rates pre-machining. 0.5° 0.6° lie range neither dislocations nor 11b, processes rolling grind strengthening, −400 2.8° reached 10. exists. function penetration Halbwertsbreite Peaks abhängig Abstand zur gemessen Abbildung direction senkrecht Spülrichtung iron, molybdenum, manganese, zinc Quantification major components uppermost (information nm), neglecting quantitatively limited accuracy measurement, Element Reflective [wt. %] Rough 26.9 23.2 3.5 2.4 0.6 0.7 31.4 35.9 34.8 34.6 2.7 3.2 similar. More 90 mass consists attributed organic contaminations ratio eliminate accompanying (rough 10), 45 35). Compared (about 90) 390) bulk 42CrMo4, investigated significantly enriched respect concentration. addition analysis, obtain p3/2 divided divalent trivalent 13 11, 12. detailed metallic, divalent, contributed 5 %, 25 70 total species, respectively. Fitting according [11]. Fit Eisen Röntgenphotoelektronenspektrums 14. behave predominantly chromium(III), extent chromium(VI). Oxygen oxides, substantial carbon-oxygen bonds. bound compounds. indicates metal-carbon bonds, occur Röntgenphotonenspektren Chrom sowie profiling became apparent duration increased, 15. over first 720 seconds sputtering, while contents decreased. completely seconds. After exclusively decrease continuously that, little From point on, lay constant %. These completely. under enrichment s. Tiefenprofile Eisen, Sauerstoff, nach iterativem Sputtern Argon-Ionen Strahl profile similar trend. rapidly slowly did contaminants likely sample. Sputtering removes peaks, valleys off shadowed sputtered immediately redeposited containing expectable dissolution. independent macroscopic (reflective surface). exact ambiguous enough. mixture indicated research groups who layered (II/III) iron-rich pattern 4, 5, 9, 13. (energy images); hydrogen methods. diffraction, probably hydroxide, whereupon oxide, exist allowed determination. occurrence chromium(VI) spectroscopy. interface metal/oxide towards oxide/electrolyte assumed. support, needs achieved pulse time pause composed time. long, uncontrolled corrosion expected take place pulse-pause whole sample, qualities. inhomogeneously Nevertheless, unambiguously. proportionally specific conductivity drop inversely removal causes flow, increase. undissolved particles insoluble hydroxides shall occurs end contrary, work, medium shiny, area. nobler merely 7, 16. At active dissolution, standard differ comparing Fe→Fe2++2e− E0 −0.44 V Fe3C→3Fe2++C+6e− −0.472 17. Considering kinetics, will certain depending pH value, potential. 18. recommended value electrochemically stress studying bonding suggests incorporation nano-diffraction option ferrite. explained (increase electrolyte) pH-value. comparison exclusive interpretation misleading nature distinctive supported German Research Foundation (DFG) transregional Collaborative Center “Process Signatures” project number 223500200-TRR 136 (Aachen, Bremen, Oklahoma), subprojects C01, C02, F03 M06. Open access funding enabled organized Projekt DEAL. service our authors readers, journal supplied authors. Such materials peer reviewed re-organized online delivery, copy-edited typeset. Technical support issues arising (other missing files) addressed Please note: publisher functionality Any queries content) directed author article.