Abstract: A comprehensive investigation of microstructure evolution upon annealing in the
temperature range between 100°C and 450°C in SPD-processed nanocrystalline iron had been
conducted using transmission and orientation imaging microscopy, and XRD analysis. The asprocessed
microstructure was typical of severely deformed metals consisting of grains with a mean
size of 110 nm, each subdivided by a network of subgrain boundaries. Additionally, measurements
of microstrains using XRD found a very high microstrain level of 0.003 in this material. After
annealing at 200°C a drastic decrease of microstrains was observed; whereas no notable changes in
the size of grains and subgrains as well in misorientation spectra have been revealed. Thus we relate
this decrease of microstrains with recovery of non-equilibrium grain boundaries. Annealing at
higher temperatures hadn’t led to further decrease of microstrains, but resulted in slight subgrain
growth from 65 to 78 nm accompanied by increase of mean misorientation angle from 5° to 6.3°at
450°C. This indicates the occurrence of coalescence of subgrains as additional recovery mechanism.
Abstract: Both the presence and absence of an amorphous intergranular film (IGF) between the
SiC grains have previously been reported in liquid-phase-sintered SiC ceramics (LPS-SiC). The
dominant factor(s) responsible for the grain boundary structure in LPS-SiC has not been clearly
revealed. In the present study, LPS-SiC ceramics containing different compositions of sintering
additives were fabricated and characterized with respect to their grain boundary structure, using both
scanning and transmission electron microscopy. The results suggest that the sintering additive
composition plays a dominant role in the evolution of grain boundary structure in LPS-SiC.
Abstract: The kinetic and structural behavior of symmetrical <100> tilt grain boundaries with rotation angles 8.4°, 12.0°, 14.3° and 16.0° were investigated in-situ in a hot stage SEM in the temperature range between 380°C and 640°C. The results revealed that depending on the rotation angle the boundary either remained straight, became faceted or curved under the driving force provided by the boundary surface tension during high temperature annealing. The transition “facetedcurved boundary” was also found to depend on temperature. The observed behavior is attributed to the anisotropy of grain boundary energy with respect to boundary inclination.
Abstract: A novel high temperature heating method in combination with automated EBSD-data
acquisition is presented. A commercially available infrared laser is utilized to heat samples up to a
temperature of about 1000°C in high vacuum in a SEM while acquiring EBSD-data of the microstructure.
First results on the γ-α-γ phase transformation between 840°C and 865°C in a microalloyed
ferritic low carbon steel is presented.
Abstract: A new method for reconstructing a three-dimensional microstructure using the focused
ion beam-orientation imaging microscopy (FIB-OIM) is introduced. The technique is important for
the study of three-dimensional microstructures of materials because it can automatically align
(register) a series of parallel sections with both topological information and orientation information
at the sub-micrometer scale. Using voxel-based tessellation, a three-dimensional microstructure is
reconstructed by registering each section. The application of the method to a cubic material is
described and, based on the reconstruction, the grain shape and grain size distribution are
Abstract: The microstructures in 3 mol% Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP)
sintered at 1100°-1650°C were investigated to clarify cubic-formation and grain-growth
mechanisms. The cubic phase in Y-TZP appeared at 1300°C and its mass fraction increased with
increasing sintering temperature. High-resolution transmission electron microscopy (HRTEM) and
nanoprobe X-ray energy dispersive spectroscopy (EDS) measurements revealed that no amorphous
layer existed along the grain-boundary faces in Y-TZP, and Y3+ ions segregated not only along the
tetragonal-tetragonal phase boundaries but also along tetragonal-cubic phase boundaries. Scanning
transmission electron microscopy (STEM) and nanoprobe EDS measurements revealed that the Y3+
ion distribution was nearly homogeneous up to 1300°C, but cubic phase regions with high Y3+ ion
concentration clearly formed inside grains at 1500°C. These results indicate that cubic phase regions
are formed from the grain boundaries and/or the multiple junctions in which Y3+ ions segregated. We
termed such a new diffusive transformation phenomenon “grain boundary segregation-induced
phase transformation (GBSIPT)”. The grain-growth mechanism is controlled by the solute-drag
effect of Y3+ ions segregating along the grain boundary.
Abstract: The stress induced migration of planar grain boundaries in aluminium bicrystals was measured. Symmetrical <100> tilt grain boundaries with misorientation angles in the range between 5.7° and 17.8° were examined. Boundary migration under a shear stress was observed to be ideally coupled to the lateral translation of grains. The measured ratios of the normal boundary motion to the lateral displacement of grains are in an excellent agreement with the respective boundary geometry. The temperature dependence of grain boundary mobility was measured, and the corresponding activation parameters were determined. The activation enthalpy of boundary migration was found to be independent of misorientation angle in the investigated misorientation range and amounts to H=1.44 eV.
Abstract: The microstructural development of cold-rolled lath martensite structure in the low
carbon steels and ultra-low carbon steels are studied and compared. In low carbon steel of
as-quenched specimens, very thin austenite films exist at boundaries of adjacent laths, but do not
exist in ultra-low carbon steel. After cold rolling for the low carbon steel, the lamellar dislocation
cells, irregularly bent laths and kinked laths regions are frequently observed and, in some instances,
the disappearance of initial lath boundaries is observed. The existence of retained austenite films
suggests that the lath boundaries rarely disappear during cold-rolling in the low carbon steel.
Abstract: The diffusion behavior of Ti3+ along basal dislocations in sapphire has been investigated
by SIMS technique. High-density unidirectional dislocations were introduced by the
high-temperature mechanical deformation, and Ti3+ ions were subsequently diffused along the
dislocations. The SIMS diffusion profiles clearly showed diffusion tail due to the short circuit
diffusion along the dislocations called pipe diffusion. Lattice diffusion coefficient and pipe
diffusion coefficient of Ti3+ at 1300°C were measured to be 1.0±0.2×10-19 [m2/sec] and 2.0±0.6×
10-13 [m2/sec], respectively.
Abstract: Quasicrystals are aperiodic long-range ordered solids with a high potential for many modern
applications. Interest is nowadays paid to the development of economically viable large-scale
synthesis procedures of quasicrystalline materials involving solid-state transformations. The
kinetics of the high-temperature phase transition from the complex ω-phase to the icosahedral
quasicrystalline (iQC) ψ-phase in AlCuFe nanopowders was here examined by in-situ time-resolved
X-ray diffraction experiments using synchrotron radiation. In-situ XRD experiments will allow
insight on the influence of uniaxial applied pressure on the kinetics of phase transitions leading to
the formation of single-phase QC nanopowders and further contribute to the optimization of
sintering procedures for nano-quasicrystalline AlCuFe alloy powders.