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Many fine particles were observed at the grain boundary fracture surface.
The maximum hardness number (near 640 HV) of the different specimens was observed to be similar, regardless of the aging temperature, but the time required to reach peak hardness increased with decreasing temperature.
Discussion Embrittlement and De-Embrittlement of the Grain Boundary.
The fracture surface showed typical grain boundary facets.
This grain boundary embrittlement is due to the precipitation of η-Ni3Ti phase at the prior austenite grain boundaries.

It was concluded that this was due to the interaction of grain refiner particles with the bridge formation mechanism observed in non-grain refined melts.
This recycled metal had of course already been inoculated with TiB grain refiner.
A reduced efficiency of the CFF may have resulted due to the presence of these grain refiner particles in the melt.
This in turn would have increased the number of inclusions entering the bed filter.
Stirring of the melt in the furnace increased the total number of inclusions as well as the number of larger inclusions reaching the filter from the furnace.

Because of these large strains, materials grains get finer.
Their results indicate that for route BC, it was kept constant when the number of passages N was increased.
The grain size was measured according to the ASTM standard E112.
The yield and total strains are increased by increasing the pass numbers.
The results of experiments indicated that the strength of the extruded materials increased by increasing the numbers of ECAE passes and hence the grain refinement.

The number of deformation steps was 12.
Number of compression steps 0 2 4 6 8 10 12 , µµµµm 0 2 4 6 8 10 12 14 16 a b Fig. 1а.
Typical microstructure formed at high values of accumulated strain (4 compression steps) - а; effect of the number of compression steps on mean grain size (b).
Discussion A decrease in the mean grain size by approximately two orders of magnitude (Fig 1b) means the nucleation of a great number of new grains during strain and allows classifying the process under study as dynamic recrystallization.
The large number of dislocation boundaries, the gradual increase of high angle boundary content and the presence of twins (Table 1) mean that the nucleation of new grains occurs via the formation of deformation-induced boundaries (dislocation and twinning ones) and their subsequent evolution.

Composition of the investigated steel a) b) c) Figure 1. a) Image quality map of the grain investigated, b) phase map of the same grain, c) Phase map of the same grain but at higher magnification showing the formation of α’ martensite at the intersection between ε bands For the sake of brevity, the results of this study will be illustrated with reference to one representative grain, illustrated in Fig. 1.
The observations made on this grain are generally representative of the results found for the 10 grains analyzed from this sample.
One way to reduce the number of arbitrary cut-offs in this method is to turn to experimental results that support the fact that not all 6 α’ variants are equally likely to form in a single ε-martensite plate.
We have found this to be true for all the grains analyzed in this sample.
This direction is readily known when the two intersecting epsilon variants are known and reduces the total number of α’ variants from 6 per ε-plate to only 2 per ε-plate.

This was attributed to the development of very thin layers of a Zn-rich grain boundary phase, which leads readily to the occurrence of enhanced grain boundary sliding at room temperature.
Homogeneous coarse-grained (CG) microstructure with an average grain size of 50 μm was observed in the annealed material.
Summary CP Cu and Al 6063 alloy were subjected to ECAP and ECAP-PC processing for varying number of passes.
Langdon, Twenty-five years of ultrafine-grained materials: Achieving exceptional properties through grain refinement, Acta Mater. 61 (2013) 51-59
Langdon, Enhanced ductility of nanocrystallien and ultra-fine grained metals, Rev.

Corrosion resistance of Si and Al-bearing ultrafine grained weathering steel T.
The ultrafine grained (UFG) weathering steel containing Si and Al showed higher corrosion resistance than carbon steel in the test.
Moreover, the principle of increasing the strength of steels by the grain refinement was shown in our 1 st project.
As the surface rust increased with the number of test cycles, Rh increased.
Fig.7 shows the results of EIS parameters on Al and Si-bearing UFG weathering steel and SM conducted after the corrosion test, showing Rrust and Rt against number of cycles.

The model considers the microstructure as a composite made of a given (discretized) number of phases which have their own specific properties.
This procedure can induce an exponential data structure increasing with the increasing number of process passes.
The other model is the Anan model (see Fig. 2 - left, bottom) [4], which consists in considering the microstructure as a composite made of a given number of small zones which have their own specific microstructure properties (grain sizes, recrystallized volume fraction, etc).
A fixed number of grain categories is associated to each finite element.
The model consists in describing the microstructure as a composite made of a given number of small zones which have their own specific grain sizes or recrystallized volume fraction.

In [38] the segregation effect for the grain boundary impurity diffusion problem was investigated for the case of an open grain model where the grains are represented by parallel slabs.
In the present paper, we analyse the GB impurity diffusion problem for the closed grain model where the grains are assumed to have a cubic shape.
The segregation effect in the cubic grain model is analysed and compared with the simple parallel slab grain model.
(14) This critical value is the same for both parallel slab grain boundaries and closed grains models.
There have been a number of attempts to develop suitable closed grain models, such as the cubic grain model introduced by Suzuoka [45], the spherical grain model developed by Bokstein and colleagues in [43], the Levine-MacCallum model for polycrystals [46].

The mechanisms of grain refinement are discussed.
The backscatter electron images in Fig. 2 show the general features of microstructural evolution with the increased number of CFAE passes.
EBSD maps of CFAE processed IF steel sheet samples, showing evolution of deformation structure with the increased number of passes: a) 1, b) 2, c) 3, d) 4, e) 6 and f) 8.
Mechanisms of grain refinement.
Summary IF steel sheets have been processed by continuous frictional angular extrusion to various total numbers of passes.