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Introduction The mechanical properties of metallic materials are strongly influenced by their dislocation struc- ture, grain size, and grain orientation.
Grain growth follows, where grain boundaries continue to move slowly, with smaller grains being absorbed by larger ones, leading to a structure with fewer but larger grains.
Al-5Ti-1B was added as a grain refiner (≈ 0.5 wt.-%).
For each spectrum, a number n of lifetime components can be found to describe the measured data as accurately as possible.
These oxide particles are far from the dominant annihilation site with I2 + I3 = 3.2% but trap a significant number of positrons.

Introduction In power plants many steam turbines have a record of their operation time over 100,000 hours and the number of such turbines will increase rapidly in the future.
Temper embrittlement is known to be caused by the segregation of impurity elements, such as phosphorus (P), tin (Sn) and antimony (Sb), to the grain boundaries which lowers the bonding strength of grain boundaries.
It is reported that the degree of the temper embrittlement of the turbine rotor depended on the extent of segregation of P at grain boundaries.
The data error ED is defined as (2) where N is the number of training patterns, ti is a target output and ai is a predicted output.
The weight error EW is defined as (3) where W is the total number of weights, wj is a weight of the neural network.

In this study, fine grain and pure Li2TiO3 powders were prepared by solid-state method at 700°C using TiO2 and Li2CO3 as raw materials.
The sintered ceramic pebbles with diameter of 1.0 mm show a smooth surface, uniform grain size and perfect sphericity.
A number of methods are available to fabricate Li2TiO3 pebbles, such as extrusion–spheronisation–sintering process [3], dry-rolling granulation process [4], sol-gel method and wet process [5].
It can be seen that the average grain size of the pebbles became larger with the increase of temperature.
As seen in Fig. 5a, the grain sizes ranges from 20µm to 50µm and no pores can be observed from the surface of pebbles.

For example, average grain size and grain boundaries in Fig. 3, of samples can cause effect on their dielectric dissipation.
The smaller the average grain size is, the more stable the conductivity of relaxation-polarization dissipation under an external alternating voltage is [5], therefore, the dielectric dissipation of nano-ceramic sample is stable in frequency range of 1K~9MHz.
Temperature characteristics of dielectric constants depend on grain structures.
Acknowledgements This work was supported by NSFC of P.R.China under grant number 50272040, Fok Ying Tong Education Foundation under grant number 91046, and Youth Foundation of Science and Technology of Sichuan Province under grant number 03ZQ026-03 References [1] J.G.

An unique feature of the HPT process is the straining under high pressure and this provides oportunities for grain refinement of less ductile materials [4,5], for production of finer grains than the other SPD processes [6] and most interestingly for possible phase transformation [7-9].
HPT was carried out on the annealed discs under a selected pressure in the range of 1.2-40 GPa with different numbers of revolutions.
Hardness increases with increasing number of revolutions, increasing distance from the disc center and increasing equivalent strain at early stages of straining.
The microstructures consist of grains with the average size of ~150 nm.
The grains are surrounded by boundaries of high misorientations and some strain associated with dislocations is present within the grains. 4.

Suppose the number of track point in each statistical area is Qi ( i=1,2,…,N).
The standard deviation SQ of the number of track point in each area can used to represent lapping uniformity: (1) Where is the average number of track point in each divided areas.
The R-type diamond grain was simulated in this study.
The grain was modeled as a half sphere subjected to the dressing force, as shown in Fig. 7.
When Δ is small enough, the contact between the diamond grain and the workpiece surface is elastic.

Fig. 3 Core material of paulownia after processing There are a number of different forming technologies of resin matrix composite structure, and different forming technologies have a significant impact on the quality and performance of composite materials.
Considering the structural characteristic of the composite materials, according to the different grain of paulownia wood, choose along with the wood grain and across the wood grain respectively in the experiment.
(a) Tension-shear test across the wood grain (b) Tension-shear test along the wood grain Fig. 7 Tension-shear test model of the composite sample In the tension-shear test across the wood grain, the typical failure phenomenon was the wood fiber abruption along the across wood grain.
In the contrast, the typical failure phenomenon of tension-shear test along the wood grain were shear destruction along the wood grain, and causing surface plate split at the same time.
While the average shear intensity along the wood grain was 3.34 MPa, the shear modulus was 209 MPa.

The main reason is that the ultrasonic impact can reduces the stress concentration in the weld toe, decrease the tensile stress, and even change to compressive stress in the weldment, the grain size in the welded joint can be refined.
Table 3 Fatigue test results Impact time Number Specimen thickness/mm Specimen width/mm / MPa Life /Cycle 60min 1 2 3 8.02 8.00 8.01 39.80 40.02 40.26 220 1.10×107 5.20×106 6.58×106 30min 4 5 6 8.03 8.00 8.04 39.92 40.03 39.89 220 4.71×106 4.06×106 3.95×106 0min 7 8 9 8.00 8.02 8.04 40.84 39.98 40.32 220 8.80×105 1.05×106 1.46×106 a)crack initiation zone of welded specimen b) crack initiation zone of treated specimen c) crack propagation zone of welded specimen d) crack propagation zone of treated specimen e)final fracture zone of welded specimen f) final fracture zone of treated specimen Fig.2 Morphology of fatigue freacture Under the cyclic load, dislocation slip and stop when meet the grain boundary.
Dislocation tangles are formed because of the dislocation slipping, and then become sub-grain, the cracking of subgrain forms micro cracks.
The main reason of plastic deformation included crystal plane slip, twin, grain boundary movement, diffusion creep and so on.
(2)The main reason for improving the fatigue life are increasing the surface hardness and refining the grain size, making the surface always in a state of compressive stress, decreasing the stess concentration in the weld toe.

After ageing treatment, most Cr rich phases precipitate in the form of sphere shape while a small amount of Cr rich phases exist in the form of acicular, and Y rich phases precipitate in the form of flake along the grain boundary.
Huang et al [1] reported that the addition of Zr can cause the simultaneous precipitations of fine Cr and Cu3Zr phases during ageing, thus blocking dislocation movement and the migration of grain boundary.
Once the ageing temperature exceeds 600°C, the electrical conductivity has a tendency to decrease.As Y rich phases are distributed along grain boundary in Cu-0.3Cr-0.2Ti-0.1Y alloy, they can hinder the electron transmission.
Furthermore, Y along with various melted impurities can form some refractory compounds to be as the nucleation sites, thus refining the grains and enhancing the hardness.
Although the purification of rare earth Y on copper matrix can increase the electrical conductivity, the number of grain boundary increases as well due to the grain refinement.

Nanocrystalline diamond film with smooth surface and uniform grains was deposited successfully on Co-cemented carbide using the bias-enhanced hot filament chemical vapor deposition (HFCVD).
Conventional diamond films can be deposited quickly and have high adhesive strength but have high surface roughness, large grains, can't be polished easily.
It can be clearly seen that the surface of diamond is very smooth; the grain size is very small.
This is related with many boundaries between diamond grains and the amorphous carbon and graphite formed in the boundaries.
While nanocrystalline diamond film has low surface roughness and small grain size, even though wears quickly at the first stage, it will become highly smooth very soon.