Search results

This is because fine-grained microstructures avoid the problem of microplasticity arising from slippage occurring among grains in the surface region.
The maximum number of cycles allowed for spectrum loading was 107.
Figure 6 shows the ferrite grain size.
Effect of ferrite grain size on fatigue properties.
Figure 12 shows the relationship between the stress amplitude and the number of cycles to failure.

Grain size and shape evaluation.
Grain boundary characteristics.
As a consequence, the number of grain boundaries between grains <111> and <100>, which have a misorientation angle of about 60 o , increases.
In order to prove this hypothesis the mean misorientation angle of three types of grain boundaries was determined: (i) between two <100> oriented grains, (ii) between two <111> oriented grains and (iii) between <100> and <111> oriented grains.
This confirms the hypothesis of grain rotation resulting from the absorption of dislocations in the grain boundaries. 0 10 20 30 40 50 60 1.39 2.77 3.79 true strain mean misorientation angle boundary between two <100> grains boundary between two <111> grains boundary between <100> and <111> grains Fig. 6.

They brought on very fine equiaxed grains.
The abscissa shows the grain area.
The number of the pixels shows how many grains were.
These represented that the grain size in this region was very fine, the number was less, and the strips were narrower.
XU Weiping: Associate Professor Master"s Supervisor, phone number:0086 3870876937,fax number:0086 7913953385 e-mail:xuweiping1203@126.com References [1] B.

On the other hand, the behavior of ultrafine-grained materials during superplastic deformation has a number of features that are not fully studied.
In particular, using the method the authors of this work obtained a homogeneous UFG structure in a number of titanium alloys with different content of the β phase [7].
A number of reflections on microdiffraction patterns located along the rings (Fig. 1a) which were obtained from the area cut by the selector diaphragm (~ 1.6 μm2) as well as dark-field images (Fig. 1b) indicate about the formation in the alloys of a grain-subgrain structure with ultrafine grain size d ~ 0.25 μm.
Pshenichnyuk Superplasticity and grain boundaries in ultrafine-grained materials, Woodhead Publishing in Materials, 2011
Naydenkin Grain boundary sliding in ultrafine grained aluminum under tension at room temperature, Scripta Mat. 66 (2012) 511-514

The results show that: Since the beginning of the two-phase region with quenching temperature, the austenite grain size from the initial 4+6 mixed crystal at 740℃, and gradually increased to 10 at 860℃; Austenite grain size and hardenability was directly proportional to the austenite grain size increased from 8μm to 36μm, the biggest change is the hardness 10HRC; Austenite grain size and impact toughness is linear, with the decrease of grain size, the impact energy increases linearly, and the austenite grain size and impact toughness curve fitting.
Effect of austenite grain size on hardenability.
Reduce the grain size, determine the level of hardenability of pearlite and ferrite easier nucleation at grain boundaries, which means increasing the grain size of ferrite and pearlite will generate greater probability [8], resulting in reduced hardenability.
Effect of austenite grain size on the impact toughness.
Grain refinement to improve the toughness of the material as the main reasons: From the perspective of grain boundaries on impact toughness, the grain boundaries are crack propagation resistance, when the grain size becomes smaller, the microstructure of the grain boundary area increases, uniform dislocation density distribution , so that the interface leading edge pileup of dislocations number is reduced, will help slow down the stress concentration, and the impurity concentration of the interface also becomes small, intergranular brittle fracture is also reduced. in addition, crystal high angle grain boundary presence to force the process, the deformation is not uniform, the grain boundary is not easy to produce plastic deformation , resulting in different crystal orientation, but also makes the plastic deformation of the discrepancies.

It is well known that, the quality of castings can be improved by grain refinement which reduces the size of α–Mg grains in the casting [5].
Normally, uniform fine grains are achieved in castings by addition of grain refiners to the melt prior to solidification [10].
It can be seen clearly from Fig. 3a that the pure Mg has coarse columnar grain structure and its grain size is about 1300 μm.
Addition of 0.5 wt% Al–4B has shown a strong grain refinement in pure Mg and the grain size is reduced to 720 μm (Fig. 3b).
When Q is large the rate of growth is small, thus allowing a large number of substrates to act as nucleation sites.

The tensile strength decreases with decreasing grain size for grain sizes larger than the specimen thickness.
By mean of uniaxial tensile tests and bending experiments, Raulea et al. demonstrated a decrease of the yield strength with a decreasing number of grains up to one grain over the thickness, and an increase with increasing grain size when the size is larger than the specimen thickness [6-9].
With increasing grain size, the number of grains decreases within the specimen volume.
(2) As the grain size exceed the specimen thickness, the tensile strength increases slowly with increasing grain size to a certain extant.
Baaijens: Grain and specimen size effect in processing metal sheets.

Study of application of time series model in grain yield predition Yueling Zhao1,a, Haiyan Han2, Liying Cao1 , Li MA 1,Guifen Chen1 1Jilin agricultural university, 130118 2Changchun university, 130118 a zyueling@163.com Keywords: grain production, time series ,modeling process, prediction model Abstract: the food forecast is very important for grain production, adjusting the important theoretical basis for grain planting structure, making the food security and agricultural sustainable development strategy.
Introduction The forecast of grain production and adjustment to ensure national food security and grain planting structure has important meaning of strategic adjustment of agricultural industry structure is the objective need of realizing agricultural modernization of food consumption dynamic grasp food consumption trend and direction of change, but the grain sown area and output continued to decline, will pose a potential threat to China's food supply and food security.
Forecasting of grain consumption is the basic theory on the basis of agriculture and grain production structure adjustment, to ensure food security for the nation's future in china.
According to China's grain consumption statistics, time series forecasting models of construction of Jilin province grain, and carries on the forecast to the future trend of per capita food consumption in china.
There are many factors influencing the extrapolation and prediction accuracy, such as consumer preferences, consumer psychology, market grain price and changes.

This grain refinement produces significantly improved mechanical properties.
Introduction Ultra-fine-grained and nano-grained crystalline materials exhibit attractive properties such as unusually high strength combined with reasonable ductility and toughness [1-10].
Schematic explanation of the grain-switching mechanism in formation of nano-grains.
For refining the size of grains in metals down to nanometres a number of passes are required.
A total number of over 30 grain orientations were measured, for which misorientations across boundaries were determined.

In recent years was developed a number of new processes of metal forming designed to produce metal with sub-ultra-fine-grained structure, the basic principle of which is realization in the process of deformation the simple shear scheme.
The number of cycles was equal to 3.
The structure of the deformed copper has a large number of twins (fig. 3a), after the deformation of the annealed copper has equiaxed grains with presence of twins (fig. 3b).
With increasing numbers of passes increases the proportion large-angle borders.
Also with increasing number of passes tends to reduce the number of doubles associated with a decrease in grain size of copper, which corresponds to the equation of Hall-Petch relation for the case of deformation twinning, which should be expected difficulty of the existence of twinning with decreasing grain size.