Advanced precipitation characterisation of Fe-alloys

Michael Schober

Research output: ThesisDoctoral Thesis

Abstract

Precipitates of a second phase are one of the most important constituents in the micro- (nano-) structure of alloys as they have a significant influence on macroscopic properties like, e.g., hardness and strength. The precipitates hinder the movement of dislocations, and therefore the adjustment of size, number density and volume fraction of the precipitates is of great importance for optimising the properties with regard to the desired application area. Understanding the prevailing precipitation reactions is also of vital importance for an adequate improvement of simulations. Thus, the characterisation of the precipitates builds the basis for the present thesis, which is part of the project: From atomistic to continuums modelling of precipitate nucleation and growth a combined theoretical and experimental approach (Grant No. P18480-N19, FWF). Continuum mechanics is a powerful tool to describe the evolution of large scale precipitations systems, whereas atomistic modelling is the tool of choice for small precipitates. The aim of the entire project is to explore and bridge the gap between atomistic modelling and continuums mechanics. The present thesis should support both, continuum mechanics and atomistic modelling and give effective values of the developing precipitates. Three-dimensional atom probe (3DAP) and small-angle neutron scattering (SANS) are two techniques which are each for itself extremely appropriate for such particle characterisation and in combination the perfect package for precipitation studying. The advantage of 3DAP is the direct measurement of atoms and consequently three-dimensional reconstructions of the analysed material as well as the included chemical information. SANS, as an indirect method, is a powerful technique detecting three-dimensional chemical and magnetic heterogeneities and density fluctuations in rather large sample volumes compared to 3DAP. The present work mainly deals with Cu and NiAl precipitates in a simple Fe matrix. Additionally, two commercial maraging steels are investigated in order to evaluate the applied analysis techniques with regard to accuracy and resolution. The motivation of the present thesis is on the one hand to provide accurate precipitation parameters for the cooperative simulation groups and on the other hand the improvement of the data analysis and treatment of the applied measuring techniques, especially the combination of the complementary methods 3DAP and SANS.
Translated title of the contributionVerbesserte Ausscheidungscharakterisierung von Fe-Legierungen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Dehm, Gerhard, Assessor B (internal)
  • Clemens, Helmut, Assessor A (internal)
Publication statusPublished - 2010

Bibliographical note

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Keywords

  • atom probe small-angle neutron scattering (SANS) precipitation reactions Fe-alloys

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