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China Keywords: Grain boundary engineering, Equal-channel angular pressing, Grain boundary character distribution, OFHC copper.
A great number of studies showed that special grain boundaries, described in low-Σ coincidence site lattice (CSL) boundaries (usually Σ ≤ 29), especially Σ3n (n=1, 2, 3) boundaries possess special chemical and mechanical properties [1-3].
The average grain size of the as-received materials was about 10 μm.
Moreover, the average grain size decreased with increasing of the strain level.
Owen, Mechanisms of grain boundary engineering, Acta Mater. 54 (2006) 1777-1783

By using new intermetallic compound grain refiners, chemical grain refinement casting technology was carried out to refine K4169 superalloy.
The results show that the grain morphology has been transformed from dendrite to granulation, the average principal axis length of the primary dendrites has been shorted and the segregation ratios of main alloy elements mitigate with the decrease of grain size in fine-grained castings, which indicates the remarkable effects of grain refinement.
of Microstructure Evolution In the past, the researches on the processing of superalloy using chemical grain refinement casting were mainly depended on test methods.It was through a large number of experiments to study the relationships between the solicitation process and the grain structure.
Conclusion The grain structure obtained by grain refining casting had a big decrease on its principal axis length of the primary dendrites, while the span of the secondary dendrites did not change much; The grain refining process went with the process of the grain morphology transformed from dendrite to granulation.
Mondolf, Grain Refinement in the Casting of Nonferrous Alloys, in “Grain Refinement in Casting and Welds”, Eds.

All the grain size values are slightly above 200 nm, except for the HPT-processed specimen having a grain size of about 160 nm.
The higher the number of passes, the lowest the thermal stability of the microstructure.
Figure 2b shows the dislocation density and the twin boundary frequency as a function of the number of ECAP passes.
These volumes may then act as the embryos for the new grains formed by recrystallization thereby reducing the time required for grain nucleation.
(b) The variation of dislocation density and the twin boundary frequency with the number of ECAP passes for Ag.

Grain maps of this martensite were initially assembled from the data sets with a grain boundary tolerance of 3-5 degrees.
Grain growth will continue at the hold temperature.
The grain growth of austenite is controlled by the grain boundary migration.
The driving force for the grain growth is grain boundary energy reduction and the mechanism related to triple point force balance and grain boundary curvature [9] .
In addition, an empirical equation describing the effect of heating rate on AC1 has been established. 5- Acknowledgment The authors are grateful for financial support from the European Commission under grant number 675715 – MIMESIS – H2020-MSCA-ITN-2015, which is a part of the Marie Sklodowska-Curie Innovative Training Networks European Industrial Doctorate programme.

The results show that as number of ECAP passes increase, the applied strain accumulated in the samples also increases and the grains change from equiaxed to elongated structure.
No Number of ECAP pass (N) Strain (ε) Average grain size, µm 1. 0 0 48.2 2. 1 0.6667 36.3 3. 2 1.3334 33.5 4. 3 2.0001 30.2 The stored energy due to ECAP process indicated by strain (ε) increased with number of ECAP pass.
The hardness of the specimens increased with the increasing number of ECAP passes.
Hardness as a function of number of ECAP passes Conclusions 1.
ECAP process make the grains elongated and smaller compared to the grains of raw material. 2.

The numbers on the micrographs indicate the lattice curvatures between the pointed micro volumes.
Also, the number of internal dislocation in grain interiors remains almost unchanged upon the treatment.
The numbers indicate the lattice curvatures within the grains.
The grain coarsening follows normal grain growth behavior with a power low function of annealing time.
Thus, the ultrafine grained microstructures evolved under severe deformation are susceptible to fast grain boundary recovery upon subsequent heating.

In this paper, it is proposed to highlight consequences of chaining DDRX and PDRX mean field models on average grain size and grain size distribution.
A mean field description of the grain structure is used: a spherical grain interacts with an equivalent homogeneous matrix whose properties are the average properties of all the grains.
Several mechanisms contribute to the evolution of the grain properties: (i) Grain Boundary Migration.
(iii) Nucleation of New Grains.
Sketch describing the relation between the number of grains within a given diameter range and the time elapsed Acknowledgements G.

Currently, adding refiner is the main method for refining aluminum grains.
When the amount of B increases to 0.04% in sample (c), it has a large number of central equiaxed grain and grain size becomes small; With the content of B increasing, the samples with boron content of 0.06%, respectively (d), 0.08% (e) and 0.10% (f) have been stably presented fine macrostructure.
A uniform and fine grain structure when the content of B runs up to 0.06% or more
Senterner, The role of boron in the grain refinement of aluminum with titanium.
Eidhed, Fading mechanism of grain refinement of aluminum-silicon alloy with Al-Ti-B grain refiners, Mater.

In order to correlate the grain boundary microstructure to IGSCC, and in general, improve the understanding to IGSCC of Alloy 132 weld metal, the grain boundary microstructure as well as IGSCC behavior of Alloy 132 was studied in this work.
Some correlations were found between grain boundary chemistry and IGSCC susceptibility in these studies.
Efforts were made to find a correlation between IGSCC behavior and the grain boundary microchemistry.
The strain rate and charging time were 2.08×10 -7 s-1 and 192hrs Fig. 5 The fracture surface of the hydrogen-charged specimen 123456789101112 0 10 20 30 40 50 60 70 Atomic concentration (at%) Facet number 123456789101112 0 5 10 15 20 25 30 Atomic concentration (at%) Facet number 123456789101112 0 1 2 3 4 5 Atomic concentration (at%) Facet number (a) (b) (c) Fig. 6 Variations (∆) and average (●) of the concentrations of (a) Ni, (b) Cr and (c) P on the IG facets plotted with those average values from TG surface (dashed line) SCC Behavior of Alloy 132 in simulated BWR environment.
The segregation of phosphorous at the grain boundary is around 1-4at%.

Lattice strains of several hkl planes of austenite respective ferrite were mapped as a function of sample direction at a number of load levels during loading into the plastic regime and unloading.
Residual stresses depending on the grain-orientation and phase have been found after unloading.
At about -550 MPa, the α-211 grain subset yields, followed by the α-200 at about -600 MPa.
Grain-orientation-dependent residual stresses have been induced in the steel.
Residual stresses depending on the grain-orientation and phase have been found after unloading.