The mobility of the Grain Boundaries (GBs) is a key mechanism which determines the microstructural evolution during growth: It controls the processes of recrystallization, grain growth, phase transformation, and precipitation. Therefore it determines the grain size and subsequently the yield strength in the post grown material.
The crystallographic microtexture and microstructure of a b-titanium alloy (Ti-35wt.%Nb-7wt.%Zr-5wt.%Ta) is studied after warm rolling and recrystallization. The main observations are the evolution of partially recrystallized microstructures during warm rolling and the formation of strong through-thickness texture and microstructure gradients at larger strains. Both, the recrystallized volume fraction and the texture depend on the thickness reduction. At small reductions (≤50%) texture gradients are also small showing some abcc–fiber (crystallographic axis <110> parallel to the rolling direction) and g–fiber (crystallographic axis <111> parallel to the normal direction) texture components. At larger strains (70-90%) the texture and microstructure gradients are characterized by shear texture components and dynamic recrystallization particularly close to the surface layers and plane strain texture components which are typical of recovered grains in the center layer.
This is a study on grain-scale micromechanics of polycrystal surfaces during plastic straining. We use Al-Mg-Si sheets (alloy AA6022) as model material. The work aims at understanding the relationship between microstrain heterogeneity and surface roughness in plastically strained polycrystals in terms of the surface and through-thickness microstructure. Experiments were conducted on polycrystals with identical composition but different processing and microstructures. We performed tensile and bending tests on sheet samples cut in transverse and rolling direction. We investigated the plastic surface microstrains (photogrametry), surface topography (confocal microscopy), particle distribution (metallography, SEM), microtexture (EBSD), and grain size distribution (EBSD) in the same sample regions. We also conducted in-situ straining experiments where the microtexture, surface topography, and stress-strain behavior were simultaneously determined. The results reveal a relationship between the heterogeneity of plastic surface microstrains, roughness, and microstructure. In particular a correlation could be established between microstrains and banded microtexture components (Cube, Goss, {111}[uvw]).
Electrodeposited nanocrystalline materials are expected to have a homogeneous grain size and a narrow grain size distribution. In CoNi electrodeposited films, however, under certain conditions an undesired columnar grain structure is formed. Fully automated three dimensional orientation microscopy by combination of precise material removal by focused ion beam (FIB) and subsequent electron backscatter diffraction (EBSD) analysis was applied to fully characterize the grain boundaries of these columnar grains in order to gain further understanding on their formation mechanisms. Two dimensional orientation microscopy on these films indicated that the development of columnar grains could be related to the formation of low energy triple junctions. 3D-EBSD allowed us to verify this suggestion and to determine the boundary planes of these triples. The triplets are formed by grain boundaries of different quality, a coherent twin on the {} plane, an incoherent twin and a large angle grain boundary. These three boundaries are related to each other by a rotation about the áñ direction. A second particularity of the columnar grains is the occurrence of characteristic orientation gradients created by regular defects in the grain. Transmission electron microscopy was applied to investigate the defects character. For this purpose a sample was prepared with the FIB from the last slice of the 3D-EBSD investigation. From the TEM and 3D EBSD observations a growth mechanism of the columnar grains was proposed.
Systematic studies allow to test/validate commonly employed ab initio approaches with respect to efficiency and accuracy in predicting thermodynamic materials properties.
Displaying results 1 to 5 out of 199
