Search results

In order to obtain the high hot-strength in high-temperature service, the alloying degree of nickel-based superalloy is increasing which leads to the decreasing the stability of microstructure during the high-temperature and long-time service, and even a lot of TCP precipitation phase at the grain boundaries which leads to the appearance of the brittle failure in a large number of caused by catastrophic the phenomena of disastrous brittle failure[2].
A large number of dimples exist in tensile fracture without aging treatment.
The precipitation phases within the grain transform to grain boundaries during the long-term aging, which increase the size of precipitation phases at grain boundaries.
The needle-like precipitation phases along the grain boundaries or growing into grain can be observed.
With prolonging aging time, grain boundary precipitation phases continue to grow, the interface of precipitation phases and substrate replace a large number of grain boundaries.

， (2) Where and are the slip/twinning plane normal and slip/twinning direction vectors, respectively, is the shear strain rate, and is the number of slip and twinning systems.
Hereafter, we term these two as grains A and B.
Twin system #5 is activated in most parts of the grain.
Fig. 2 Enlarged views of Fig. 1: (a) grain A and (b) grain B.
Fig. 4 Histories of resolved shear stress in grain A.

The number of atoms sitting in or affected by the grain boundaries is indeed rapidly increasing: for instance in a 20nm sample this amounts at least 10% of the atoms.
Two type of samples are used in this study: (1) a selfsimilar structure having 15 grains with mean grain sizes of 5, 12 and 20 nm and (2) a sample with 125 grains with a mean grain size of 6 nm.
A sample with 125 grains and a mean grain size of 5nm was choosen.
A large number of grains are necessary in order to minimize the effects imposed by the periodicity used to simulate bulk conditions.
The small grain size is chosen to reduce the total number of atoms in the sample (to 1.2 million) so that longer deformation times are possible at acceptable strain rates.

Sr as modifier and TiB as grain refinement elements.
The grain size was measured by Grain Size Planimetri method.
While the addition of TiB on the Al matrix as grain refiner and worked efficiently with higher reinforce particles especialy for Al/SiC composites as seen in Fig.4, where grain size slightly dereased from 5.6 to 6.01 ASTM Grain Number, while for Al/Al2O3 composites the grain size is also decreased from 5.3 to 6.02 ASTM Grain Number (see Fig.5).
ASTM Grain Number of Al/SiC and Al/Al2O3 composites on Fig.4.
The higher ASTM Grain Number the lower grain size of the mirostruture and generated higher strength and hardness.

The microstructure was characterized by equiaxed grains of about 40 μm with a large number of ∑3 annealing twins.
The microstructure was characterized by elongated grains with profuse lamellar features.
In order to characterize the nucleation rate during recrystallization the number of recrystallized grains per unit volume was estimated in specimens after different annealing times.
At both the lowest (560°C) and the highest (670°C) annealing temperature the number of recrystallized grains per unit volume reached the maximum values after very short annealing times and remained virtually the same on further annealing, i.e. nucleation was site saturated.
The nucleation of new grains was site saturated.

Dimple and a number of torn edges appeared in the fracture surface after 4 passes of ECAP.
With the passes of ECAP increasing, the material got strong plastic deformation, resulting in a large number of dislocation and serious grain boundary distortions which produce more sub-grain to be recrystallization nucleus and produce the driving force for dynamic recrystallization.
The mechanical properties, except the relationship with matrix α-Mg, depends largely on the particle shape, size, number and distribution of Mg2Si phase [[] S.L.
For fine-grained materials, the stress can be distributed to more grains, thus reducing the stress of each grain.
The smaller grain sizes, the development of deformation coordination of the grain boundary.

In particular, we focus on the effect of misorientation at grain boundary or phase interface on the kink evolution.
The specimen is constituted by two α-Mg phases (grains 1, 3) and LPSO phase (grain 2) and the displacement in the z-direction is constrained to prevent the structural buckling.
The specimen dimensions are in height, in width, in thickness and the following initial shape imperfection in the x-direction is introduced: , (8) where the superscript denotes the node number, both and the imperfection amplitudes and is the wave number.
We let the values of amplitude be 0.01 and 0.005 and the wave number be .
A large number of non-basal slip, in particular the pyramidal ones, in α-Mg phases is observed near the grain boundaries and kink bands.

Due to their dissimilar properties and different deformation mechanisms between grain interior (GI) and grain boundary affected zone (GBAZ) in the nanocrystalline (NC) materials, a two-phase composite model consisting of GI and GBAZ was developed and adopted to build strain gradient plasticity theory.
Introduction Compared with conventional coarse-grained polycrystalline metals, nanocrystalline (NC) materials are structurally characterized by a large volume fraction of grain boundary (GB), which may significantly affect their overall physical, mechanical and chemical properties.
For the sake of simplicity, these grains will be further idealized as spherical inclusions.
According to geometrical deformation condition, shear strain γG�Ds created by GNDs can be obtained / G�Ds GBAZ GI GSnb d γ γ γ φ = − = (1) where n is the number of GNDs around the GI in a single grain, dGS is grain size, φ is the geometrical factor and b is Burgers vector.
It can be seen that the predictions are in good agreement with the experimental results, especially for grain size 23 nm with higher plasticity hardening rate.

Spherical grains are excessive alumina after burning or dissolvable phase.
The results showed that rod-like Crystal is very likely the CaCO3 and MgCO3 [9].The reactions are as follows: As shown in Fig. 3g the rod-like crystals become thick but the number of them is reduced after hydration for 24h.
Instead there appear a large number of mesh or beard shape crystals.
The stick big grains are not appeared.
The stick big grains are not appeared.

Thereby it reduces the number of shutdown to ensure the safe operation of the boiler and create the favourable vield and social benefits.
It clearly shows there is a clear boundary line and discontinuous columnar crystal in sample 1.The organization is uneven and there is a large number of bright coarse-grain on the left side.
And the grain is very small.
And the grain tapered from the inside out.
Then it is coarse-grained zone and fine-grained zone.