TY - BOOK

T1 - Deformation in technical bcc and fcc materials - mechanical and correlative microstructural analyses

AU - Weißensteiner, Irmgard

N1 - no embargo

PY - 2018

Y1 - 2018

N2 - This thesis comprises studies of the deformation behavior of application-relevant engineered alloys, namely Co-Cr-W-Mo, Co-Cr-Mo as well as an advanced high-strength steel in different microstructural morphologies, which were adjusted by varying the overageing temperature in isothermal heat-treatments. The resulting microstructures, ranging from granular bainite over lath-like bainite to (tempered) martensite were tested in tensile tests, bending tests and hole expansion tests. The performance in the mechanical tests as well as the resulting microstructure correlates to the local changes in texture. Homogeneously deformed microstructures develop strong α-fibers (〈110〉||rolling direction). In the microstructures forming a heterogeneous dislocation structure, an increase of ε-fiber fraction (〈110〉||transverse direction) can be observed after deformation. Comparable to advanced high-strength steels, the constituent phases and their morphology also strongly influence the formability of Co-Cr alloys, although the underlying mechanisms are different. External mechanical loading of typical Co-Cr implant alloys can lead to a deformation-induced martensitic phase transformation (DIMT) from the metastable high-temperature fcc γ-phase to the hcp ε-phase, which is the stable room temperature modification. Nanoindentation tests on a Co-Cr-W-Mo alloy revealed a decrease in the tendency to DIMT due to hot isostatic pressing. The explanation for this is a slight change in the chemical composition as proofed by atom probe tomography. The onset stress and strain for DIMT were determined by means of in-situ compression experiments. A correlation with the stress-strain curves showed the simultaneous onset of plastic deformation, the reduction of the elastic lattice strains in the γ phase and DIMT, which can be interpreted as a confirmation of the strain-induced nature of the phase transformation. Compressive deformation of the Co-Cr-W-Mo alloy with low stacking fault energy leads to the formation of a 〈110〉γ fiber texture and an alignment of the {111}γ planes parallel to the radial direction. In the analysis of both material classes, the combination of different testing and analysis methods was the key to interpret the mechanisms behind the macroscopic behavior and, consequently, also to improve the materials suitability for applications of growing complexity.

AB - This thesis comprises studies of the deformation behavior of application-relevant engineered alloys, namely Co-Cr-W-Mo, Co-Cr-Mo as well as an advanced high-strength steel in different microstructural morphologies, which were adjusted by varying the overageing temperature in isothermal heat-treatments. The resulting microstructures, ranging from granular bainite over lath-like bainite to (tempered) martensite were tested in tensile tests, bending tests and hole expansion tests. The performance in the mechanical tests as well as the resulting microstructure correlates to the local changes in texture. Homogeneously deformed microstructures develop strong α-fibers (〈110〉||rolling direction). In the microstructures forming a heterogeneous dislocation structure, an increase of ε-fiber fraction (〈110〉||transverse direction) can be observed after deformation. Comparable to advanced high-strength steels, the constituent phases and their morphology also strongly influence the formability of Co-Cr alloys, although the underlying mechanisms are different. External mechanical loading of typical Co-Cr implant alloys can lead to a deformation-induced martensitic phase transformation (DIMT) from the metastable high-temperature fcc γ-phase to the hcp ε-phase, which is the stable room temperature modification. Nanoindentation tests on a Co-Cr-W-Mo alloy revealed a decrease in the tendency to DIMT due to hot isostatic pressing. The explanation for this is a slight change in the chemical composition as proofed by atom probe tomography. The onset stress and strain for DIMT were determined by means of in-situ compression experiments. A correlation with the stress-strain curves showed the simultaneous onset of plastic deformation, the reduction of the elastic lattice strains in the γ phase and DIMT, which can be interpreted as a confirmation of the strain-induced nature of the phase transformation. Compressive deformation of the Co-Cr-W-Mo alloy with low stacking fault energy leads to the formation of a 〈110〉γ fiber texture and an alignment of the {111}γ planes parallel to the radial direction. In the analysis of both material classes, the combination of different testing and analysis methods was the key to interpret the mechanisms behind the macroscopic behavior and, consequently, also to improve the materials suitability for applications of growing complexity.

KW - Plastische Verformung

KW - Advanced High-Strength Steels

KW - Co-Cr

KW - Implantatlegierung

KW - Textur

KW - Mikrostruktur

KW - Plastic Deformation

KW - Advanced High-Strength Steels

KW - Co-Cr

KW - Implant Alloy

KW - Texture

KW - Microstructure

M3 - Doctoral Thesis

ER -