TY - THES

T1 - Intermetallic NiAl precipitate analysis by means of atom probe and complementary methods

AU - Lerchbacher, Christoph

N1 - embargoed until null

PY - 2009

Y1 - 2009

N2 - Technically relevant structural materials gain their exceptional mechanical properties from several microstructural features. One of these features is the fine dispersion of second phase particles such as precipitates which reduce the dislocation mobility, thus, increasing the strength of the material. Their influence on the mechanical properties of the material is controlled by characteristics, like size distribution, shape, number density and volume fraction. The control of these characteristics by performing appropriate mechanical and thermal treatments to gain the required microstructure is of great interest for materials producing and processing industry. Investigations are preferably performed on model alloys, due to the fact that in simpler systems it is easier to identify and characterize precipitation reactions as it is in complex technical materials. The B2 ordered intermetallic NiAl phase has been identified to be responsible for strengthening effects in several Fe-based materials. For reasonable simulations of the development of characteristics like composition, size, distribution or shape of the precipitates the early stages have to be understood. Due to high sensitivity and resolution especially the use of atom probe (3DAP) and small-angle neutron scattering (SANS) is suitable for analyzing the results of precipitation reactions. In order to obtain information on the transformation kinetics differential scanning calorimetry provides high resolution as well. The advantage of SANS is that quantitative values like size and number density of the precipitates can be measured within a large volume compared to direct microscopy, such as atom probe. Additionally, the magnetic and nuclear scattering contrasts between matrix and precipitates provide information on their chemical composition development. Implementing in-situ SANS experiments enables the observation of the development of precipitation parameters and chemical composition. In combination with 3DAP measurements the results can be critically compared and the applicability and the accuracy of the complementary characterization methods can be assessed. The intention of the present work is the characterization of the precipitation behavior of a Fe-based model alloy with additions of Al and Ni. Three ferritic alloys with different additions of Al and Ni have been produced and investigated by the mentioned characterization methods.

AB - Technically relevant structural materials gain their exceptional mechanical properties from several microstructural features. One of these features is the fine dispersion of second phase particles such as precipitates which reduce the dislocation mobility, thus, increasing the strength of the material. Their influence on the mechanical properties of the material is controlled by characteristics, like size distribution, shape, number density and volume fraction. The control of these characteristics by performing appropriate mechanical and thermal treatments to gain the required microstructure is of great interest for materials producing and processing industry. Investigations are preferably performed on model alloys, due to the fact that in simpler systems it is easier to identify and characterize precipitation reactions as it is in complex technical materials. The B2 ordered intermetallic NiAl phase has been identified to be responsible for strengthening effects in several Fe-based materials. For reasonable simulations of the development of characteristics like composition, size, distribution or shape of the precipitates the early stages have to be understood. Due to high sensitivity and resolution especially the use of atom probe (3DAP) and small-angle neutron scattering (SANS) is suitable for analyzing the results of precipitation reactions. In order to obtain information on the transformation kinetics differential scanning calorimetry provides high resolution as well. The advantage of SANS is that quantitative values like size and number density of the precipitates can be measured within a large volume compared to direct microscopy, such as atom probe. Additionally, the magnetic and nuclear scattering contrasts between matrix and precipitates provide information on their chemical composition development. Implementing in-situ SANS experiments enables the observation of the development of precipitation parameters and chemical composition. In combination with 3DAP measurements the results can be critically compared and the applicability and the accuracy of the complementary characterization methods can be assessed. The intention of the present work is the characterization of the precipitation behavior of a Fe-based model alloy with additions of Al and Ni. Three ferritic alloys with different additions of Al and Ni have been produced and investigated by the mentioned characterization methods.

KW - NiAl Ausscheidung Atomsonde 3DAP SANS Neutronenkleinwinkelstreuung

KW - NiAl precipitation atom probe 3DAP SANS small angle neutron scattering

M3 - Diploma Thesis

ER -