Preparation of nanostructured iron by mechanical milling under cryogenic conditions
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hdl:2099.1/17622
Tipus de documentProjecte Final de Màster Oficial
Data2012-09
Condicions d'accésAccés obert
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Abstract
Fabrication of nanostructured materials is of outmost importance for future advanced
materials. Nanostructurization of materials with structure sizes in the micrometer range and
below can significantly alter mechanical and physical properties while using the identical
chemical composition as their counterparts. Up to now there are only few approaches on
synthesizing large amounts of bulk nanostructured materials and micromechanics of the
fabrication process are not completely understood and characterized.
This work develops and investigates a new production process for nanostructured pure iron
via cryomilling using a SPEX freezer/mill. Based on the creation of an experimental design
and the definition of a process protocol multiple sample series were fabricated to investigate
influences of individual parameters. Laser diffraction analysis and scanning electron
microscopy (SEM) were used to characterize powder evolution with varied milling times,
milling loads and milling rates.
It was found that increasing milling times promote a homogenization of the particle size
distribution and the creation of nanoparticles due to brittle fragmentation triggered by the
employed cryogenic temperatures. Increasing milling loads augmented the probability to
create micrometer-sized particles. Lower milling rates increased plastic deformation
processes and particle agglomeration mechanics during the milling process.
Fabricated iron nanoparticles were used to synthesis bulk specimens by a cold and
subsequent warm consolidation process. Created microstructure samples were analyzed by
Vickers hardness micro indentation tests, by using optical microscopy and SEM and by
electron backscatter diffraction. Vickers hardness was found to increase with milling time up
to a maximum of 569 HV with a testing load of 0,02 kg. SEM analysis proved that former
nanoparticles were conserved during the consolidation process forming grains with minimum
grain sizes of less than 20 nm. Larger particles showed a plastically deformed grain structure
with micrometer sized flattened grains including low angle grain boundaries. Those and the
formation of a few nanograins inside former large particles were accorded to a severe plastic
deformation process. Micro tensile testing was performed after heat treatment of 30 min at
650°C. All samples showed a brittle fracture behavior that is most likely linked to compaction
flaws like pores and other observed inhomogeneities.
MatèriesIron -- Mechanical properties, Iron -- Microstructure, Nanostructures, Low temperature engineering, Ferro -– Propietats mecàniques, Ferro -– Microestructura, Nanoestructures, Temperatures baixes -- Enginyeria
TitulacióMÀSTER UNIVERSITARI ERASMUS MUNDUS EN CIÈNCIA I ENGINYERIA DE MATERIALS AVANÇATS (Pla 2014)
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JonathanGermannMasterThesis.pdf | Report | 33,24Mb | Visualitza/Obre |