Abstract: This research looks at the influence of annealing treatments on twins in magnesium alloy
AZ31. Samples containing different twin fractions are created in order to examine the influence of
the initial structure on the annealing behavior. It is seen that twins can both expand, taking over an
entire grain, or shrink, leaving completely untwinned grains. The grains, containing expanding
twins, are found to contain, in general, only one twin variant and limited slip deformation after twin
formation. The grains containing shrinking twins, on the contrary, are seen to contain different twin
variants and have undergone more slip deformation after twinning.
Abstract: The effect of low temperature recovery treatments on the recrystallization kinetics during
subsequent high temperature annealing was investigated in three Al-2.5%Mg alloys with various Fe
additions. Recovery treatments were carried out at 190oC for times ranging from 0.25 to 65 hrs.
Recrystallization treatments were carried out at 280oC. The kinetics of recrystallization was
followed using the techniques of hardness measurement, optical metallography and calorimetry.
Abstract: Anisotropy of grain boundary motion in a Fe–6at.%Si alloy is represented by a spectrum
of values of the activation enthalpy of migration and the pre-exponential factor, depending on the
orientation of individual grain boundaries. The general plot of these values exhibits a pronounced
linear interdependence called the compensation effect. It is shown that changes of these values,
caused by changes of intensive variables, are thermodynamically consistent.
Abstract: The microstructure and texture in dynamically recrystallized copper and two copper – tin
alloys (2wt% and 4.5wt% tin) has been investigated. Specimens were deformed in channel-die
plane strain compression to true strains from 0.1 to 1.22 within the temperature range 200°C to
700°C, and the resulting microstructures were investigated with the use of high resolution electron
backscatter diffraction (EBSD). Dynamic recrystallization was initiated by the bulging of preexisting
high angle grain boundaries (HAGB), and occurred primarily by strain induced boundary
migration (SIBM) and twinning. The addition of tin led to an increase in the temperature at which
dynamic recrystallization initiated, and furthermore to a smaller dynamically recrystallized grain
size. This was attributed to the effects of solute drag causing lower HAGB mobility. Dynamic
recrystallization was observed to weaken the deformation texture components of brass and Goss, as
well as introduce a cube texture component which generally tended to strengthen with temperature
but weaken with increasing tin additions.
Abstract: Copper and gold bonding wires were characterized and compared using electron
backscatter diffraction (EBSD). During drawing, <111> and <100> fiber textures are the main
components in the wires and shear components are mainly located under the surface. Grain average
misorientation (GAM) and scalar orientation spread (SOS) of the <100> component in copper and
gold bonding wires are lower than those of the <111> or other orientations. The bonding wires
experience three stages of microstructural changes during annealing. The first stage is subgrain
growth to keep elongated grain shapes overall and to be varied in aspect ratio with annealing time.
The grain sizes of the <111> and <100> components increase during annealing. The volume fraction
of the <100> component increases whereas that of the <111> decreases. The second stage is
recrystallization, during which equiaxed grains appear and coexist with elongated ones. The third
stage is grain growth which eliminates the elongated grains and enlarges equiaxed grains. The <111>
and <100> grains compete with each other and the <111> grains grow faster than the <100> grains
during the third stage.
Abstract: In this work the pinning forces exerted by TiN particles in the austenitic phase in two Ti
microalloyed steels have been determined and compared with the driving forces for austenite grain
growth and for static recrystallisation between hot rolling passes, respectively. TiN precipitate sizes
were measured by transmission electron microscopy (TEM) and the precipitated volumes were
calculated. These results were then used to calculate pinning forces. The driving forces for
recrystallisation were found to be approximately two orders of magnitude higher than the pinning
forces, which explains why the austenite in these steels barely experiences hardening during rolling
and why the accumulated stress prior to the austenite→ferrite transformation is insufficient (low
dislocation density) to refine the ferritic grain.
Abstract: The (relative) grain boundary energy of random high angle boundaries has been measured
in several Fe-based polycrystals. Crystallographic data obtained by orientation contrast microscopy
(OIM) are combined with the geometrical configuration of grain boundaries at triple junctions. A
two-parameter representation of the relative grain boundary energy in terms of misorientation angle
and misorientation axis is presented. In the applied procedure a variation of the energy values
assigned to one boundary was observed depending on the triangulation path chosen by the operator
to connect the arbitrary initial boundary with the boundary under consideration. Results show no
evidence of correspondence between the observed energy cusps and the presence of CSL
Abstract: The austenite static recrystallization kinetics at several temperatures and the
recrystallization-precipitation-time- temperature (RPTT) diagrams of a medium-carbon vanadium
microalloyed steel have been determined for a strain ε = 0.35. Unlike many other studies carried out
previously on V microalloyed steels, the recrystallized fraction against time curves showed the
formation of a double plateau that indicates two stages of inhibition of recrystallization due to the
formation of different types of strain induced precipitates. This work makes use of transmission
electron microscopy to study the nature and size distribution of these precipitates capable of inhibiting
recrystallization. The values of driving and pinning forces for static recrystallization are calculated
and an analysis of the relationship between the net balance of these forces, the precipitation state and
the progress or inhibition of the recrystallization is accomplished. A value of driving force that
decreases as recrystallized fraction grows during isothermal holding time is estimated and helps to
interpret the behavior of austenite after deformation.
Abstract: The phenomena of strain hardening, strain induced martensite formation, recovery,
martensite reversion and recrystallization have been studied in austenitic stainless steels of the AISI
304L and 316L types, after solution annealing, followed by rolling at different temperatures (-196,
25, 100 and 200°C) and subsequent annealing of the worked samples. Strain hardening and the
percentage of α’ martensite formed showed strong dependency with the deformation temperature
and with the austenite chemical composition. As expected, both strain hardening as well as the
amount of the martensite formed was higher in the 304L steel and for lower temperatures.
Reversion temperature of the α’ martensite was close to 550°C for both steels, independent of the
amount of martensite. The 316L steel presented a higher resistance to recrystallization when
compared to the 304L steel. The recrystallization temperature of both steels was about 150°C higher
than the α’ phase reversion temperature. Rolling temperature did not influence significantly the
recrystallization temperature. Proper thermal and mechanical treatments lead to interesting
combinations of mechanical properties in both steels with values such as yield strength YS of about
1000 MPa, with an elongation around 10%.
Abstract: The influence of initial grain size on the softening-precipitation interaction in a low
niobium microalloyed steel has been investigated. The study has revealed that for the largest initial
grain size (1000 μm), the recrystallised fraction remains lower than the softening fraction until
relatively long times are reached. In contrast, for the smallest initial grain size (166 μm) both
magnitudes are similar. As a result, precipitation interacts with recrystallisation in the case of the
finest austenite grain size, whereas for the coarsest one, since recrystallisation is significantly
retarded, interaction with recovery process is observed. Apparently, the initial austenite grain size
does not affect precipitation kinetics.