In-situ atmosphere monitoring of the debinding of PM steel components with large amounts of organic additions October 12 th 216 Peter Quadbeck, Alexander Strauß, Bernd Kieback, Olaf Andersen
Fraunhofer IFAM Dresden Fields of Competence Cellular Metallic Materials Sintered and Composite Materials Fiber Structures Hollow Spheres Metal Foams Lightweight Materials Tribology PM Technologies 3D Metal Printing 3D Wire Structures Porous Metal Paper Thermoelectrics Thermal Management High-temperature and corrosionresistant Materials Hydrogen Technology Energy und Thermal Management Elektrolysis Storage Hydrolysis Heat Storage Systems Simulation Analysis
Introduction PM technologies with high organic contents Metal Injection Moulding Cellular Metals Porous Implants Micro MIM Catalytic Converter Carrier
Introduction PM Technologies With High Organic Contents Debinding of organic additives Degradation and transportation of large amounts of gasified organic materials Amount is dependent on process parameters and component properties High risk of carbon residuals with high organic contents Pressed PM Parts Cellular Metals MIM Organic material wax, stearic acid, PVA, Tylose, EPS, PUR, PP, PE, POM Organic content ~ 2 m.% ~ 15 m.-% ~ 15 m.-% Component size 1 2 1 1 mm 1 2 1 1 mm 1 1 1 mm
Experimental: Debinding of Hollow Sphere Structures Manufacturing of Hollow Sphere Structures Coating Fluidised bed Component production moulding machine Technology from established mass production processes Heat treatment debinding/sintering Coating technology from pharmaceutical industry Processing from packing industry Sintering from metal injection moulding
Introduction Early Stages of Heat Treatment Debinding Mechanisms Thermal decomposition of organic materials in multiple steps Decomposition temperatures dependent on chemical composition process drying carbonizing gas formation temperature 1 2 C 2 5 C 5 12 C mechanisms evaporation of water side group scission of higher molecular weight substances decomposition of backbones into liquid and gaseous forms solid carbon reduction and decarburization:, CO, CO 2, CH 4, etc.
Experimental Setup In Situ Atmosphere Monitoring via FTIR and MS IR window furnace Method Optical in-situ analysis of gas phase composition FTIR MS PM components In-situ-measurement gives direct correlation between gas phase composition and process parameters (e.g. temperature, gas flow, ) Measurement in tube furnace and continuous belt furnace possible
Absorbance absorbance Experimental Setup Typical Spectra Taken at Different Temperatures,4,3,2,1 O C-H (CH 4 ) CO 2 O C-H (CH 4 ) 53 C 119 C 381 C 448 C 647 C 854 C 98 C 147 C -,1 4 35 3 25 2 15 1 wave Wellenzahl number [cm [cm -1 ] -1 ] 8
Experimental Setup In-situ Atmosphere Monitoring Identification of single species Reference spectra (CO, CO 2, CH 4 ) Spectra taken in temperature steps of 5 K Calculation of relative concentration Baseline between defined fixed points Integrating area between the baseline and measured absorbance absorbance defined min. defined min. wave number O CH 4 CO 2 CO C 2 min [cm -1 ] 389.59 385.33 2331.32 2118. 948.81 max [cm -1 ] 3892.49 386.18 2332.82 212.35 96.26
Experimental Setup Materials Metal powder: stainless steel 43L Fe C Si Ni Cr Mn bal..3 <1. <.75 16. - 18. <1. Organic ingredients binder polyvinyl alcohol methyl cellulose template expanded polysterene
Results Heat Treatment in N 2 - Initial heat treatment Decomposition of polymeric backbone Styrene hydrogenates in further steps into ethylbenzene, toluol and ethene Species identified as aromatic hydrocarbons and alkene Side group scission of polyvinyl alcohol: formation of alcohol Decomposition process is completed at ~5 C integrated absorbance peak area 3,6 2,4 1,2,8,4 2 1 2 1,1,1,3,1 2 4 6 8 1 12 alkene aromates alcohol O C 2 H 4 CH 4 CO 2 CO 2 4 6 8 1 12 temperature [ C] stainless steel 43L polystyrene template N 2 - atmosphere
Results Heat Treatment in N 2 - Reduction of steels: Formation of sinter necks needs reduction of surface oxides Cr alloyed steels: no surface oxide reduction below 8 C Reduction reactions via MeO + Me + O MeO + C Me + CO MeO + CO Me + CO 2 Carbothermic reduction requires sufficient carbon content integrated absorbance peak area 3,6 2,4 1,2,8,4 2 1 2 1,1,1,3,1 2 4 6 8 1 12 alkene aromates alcohol O C 2 H 4 CH 4 CO 2 CO 2 4 6 8 1 12 temperature [ C] stainless steel 43L polystyrene template N 2 - atmosphere
Results Pure Hydrogen Atmosphere Effect of pure hydrogen Gas formation resembles the formation under N 2 - atmosphere Peaks of gas formation are more pronounced Main difference: much stronger formation of methane with a maximum at 6 C integrated absorbance peak area 2 4 6 8 1 12 8 alkene stainless steel 43L 4 polystyrene template H 2 atmosphere 2 aromates 1 4 alcohol 2,4,5,5,2 O CH 4 CO 2 CO 2 4 6 8 1 12 temperature [ C]
Results Preoxidation Treatment integrated FTIR absorbance peak area,3,2,1 ion current intensity [1-11 A] 7 6 5 4 3 2 1 m16 : temperature O m44 2: CO 4: time [hh:mm] stainless steel 43L predebindered Ar ArO 2 (97/3) FTIR CO MS 6: O m16 m44 6 5 4 3 2 1 temperature [ C] Oxidative Treatment Samples pre-debindered in Ar Oxidation in 3% O 2 atmosphere Oxygen uptake at T>2 C Carbothermic CO formation with maximum at 456 C Only low decarburization effects by oxidative treatment below 6 C Main goal: oxygen supply to the system via metal oxide formation in order to enhance carbothermic reduction at higher temperatures 14
Results Reduction in Pure After Preoxidative Treatment Much more pronounced reduction processes via MeO + Me + O MeO + C Me + CO MeO + CO Me + CO 2 Formation of a methane double peak at temperatures of 57 C and 675 C direct methane formation and masked carbothermic reaction integrated absorption area CO CO 2 CH 4 O stainless steel 43L atmosphere preoxidized in ArO 2 (97/3), 6 C debindered in Ar 4 8 12 temperature [ C]
Results Direct Methane Formation Control Experiment 12 CH 4 concentration [1-4 ] 11 1 9 8 7 6 5 4 3 nanocarbon particles wrapped in glas wool atmosphere Methane formation on graphite Nanographite wrapped in glas wool Heating in pure hydrogen Methane formation with maximum at 55 C Direct formation via 2 1 1 2 3 4 5 6 C + 2 CH 4 System is far away from equilibrium temperature [ C] 16
Conclusions Heat treatment of stainless steel 43L components with polystyrene templates and PVA binder: Decomposition of molecular backbone in N 2 - : high amounts of alcohol, aromatic compounds and alkene up to 5 C Pure atmosphere: pronounced decarburization due to methane formation at 6 C Industrial N 2 - (95/5) atmosphere: methane formation can be almost completely neglected Reduction in after pre-treatment in Ar-O 2 (97/3) atmosphere: two significant methane peaks at 57 and 675 C reactions attributed to direct methane formation and a masked carbothermic reduction
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Results Reduction after Preoxidative Treatment Erratum! Methane formation Lower peak: direct methanization via C + 2 CH 4 Second peak only visible due to high oxygen content: masked carbothermic reduction CO + 3 CH 4 + O integrated absorption area CO CO 2 CH 4 O stainless steel 43L atmosphere preoxidized in ArO 2 (97/3), 6 C debindered in Ar 4 8 12 temperature [ C] debinding atmospheres: Carbon content in ~.4 % lower than in Ar