Search results

During extrusion with grain coarsening the effect of t-ZrO2 to m-ZrO2 transformation toughening increased because more zirconia grains reached the critical dimension.
Stress induced phase transformation only take place in those tetragonal zirconia 15 mm 150 Fig.1 TEM micrograph of as-sintered materials with average grain size of 230nm(The dark particles are zirconia grains and the large bright grains are alumina grains.)
Fig.2 Blank and extruded ceramic blade model deformed at 1650°C grains whose grain size is larger than the critical size, which is about 500nm to several micron [8].
Because of the growth of zirconia grains during deformation, the amount of zirconia grains whose dimension was larger than the critical size increased.
Acknowledgements This work was supported by the National Natural Science Foundation of China under grant number of 50505005.

A count of the number of MF and MS grains per unit area (NMF and NMS, respectively) confirms the qualitative observation that there is a higher amount of MgO-fused aggregates in the refractory B.
brick MS (%) MF (%) Matrix (%) NMF NMS area (mm2) B 5 39 56 69 23 277 C 34 17 49 40 56 308 Considering the analyzed area in each brick, the number of grains per unit area (1 cm2) of magnesia-fused aggregates (δMF) and magnesia-sintered aggregates (δMS) are calculated.
Fig. 2a shows a MgO fused grain (brick B), the presence of triple points (CaO/SiO2 ~ 0.7) within the grain is observed.
MgO fused grain in (a) brick B, and (b) brick C.
In micrograph of Fig. 4a, corresponding to brick B, disaggregated MgO grains and large number of smaller rounded crystals of magnesia are observed.

The influence of the reduction of the grain size on the fatigue resistance of various metals an alloys is described in a number of papers [2,6,7].
Quantitative metallography was employed to characterise the grain size.
The interior of elongated grains was fragmented by subgrains with low-angle boundaries.
For example, according to [9] the fatigue endurance limit of the notched coarse-grained Ti samples (αт=2.8) with the number of cycles to fracture 10 6 is only 262 MPa.
Another approach to increase the ductility and at the same time preserve high strength of UFG materials is the formation of a structure with bimodal grain distribution in which nanocrystalline grains provide strength and larger grains facilitate a high ductility during deformation [7].

The crystallization ratio and grain size of the silicon thin film become larger when D is higher.
Meanwhile, H2 dilution enhances crystallization of the films and makes the grain arrange orderly.
Fig.2 The dependence of crystallization ratio on different H2 dilution Fig.3 The dependence of grain size on D By calculation, the size of silicon thin film grain on glass substrate increases from 2.98 nm to 8.79 nm.
It is noteworthy that the grain size has a substantial increase in the D = 98% to 99%.
It will do harm to the crystallization and uniformity of silicon thin films when the powder fall onto the film surface.However, reaction of H2 and SiH2 can not only reduce the SiH2, but also generate re-used SiH4 due to the existence of a large number of H2.

The average WC grain diameter was approximately 0.45μm.
So, the aggregate of several WC grains or coarse WC grain with sizes of 6 – 7 mm in diameter become the fatigue crack initiation site for the present fine grained WC-Co material.
Figure 6 shows the variation of crack lengths, 2a as a function of number of cycles, N.
(2) The aggregate of several WC grains or coarse WC grain with sizes of 6 - 7 mm in diameter become the fatigue crack initiation sites for the present fine grained WC-Co material.
(3) The fatigue lifetime can be approximated by the crack propagation life, and the number of cycles spent in crack initiation can be neglected

Mean size of the grain is 20~30 [μm] which is smaller than the un-deformed area grain size see fig 3-d.
According to the grain size change, the small grain is the more capability to block the sliding.
The corresponding figures from the serial number in Figure5, table 2.
Grain refinement will block the grain to sliding and increase the yield limit.
According to the grain size change, the fatigue strength of the alloy has a relevance to the grain size.

Although the size the utra-fine equiaxed grain is quite different from one to another, an average grain size about 0.7�m has been obtained.
The dislocations are distributed both in the grain and in the grain boundary.
The grains have evolved into more regular equiaxed shape and the average grain size becomes a little bit larger to about 1�m.
The enhanced grain boundary diffusion is caused by the fact that ECAP-processed alloys possess non-equilibrium grain boundaries.
The results show that ECAP shows an excellent capability of grain refinement, with the pass number of pressing, the grain of pure Al can be refined to about 700nm.

Herewith, the casting possesses a fine-grained structure an does not have burning-on.
The authors of the papers have conducted a number of studies of the pouring temperature influence on the structure and properties of tin base bronzes.
With the increase in the casting thickness and a rise in the pouring temperature the number of equiaxed crystals rises.
In thin (5 mm) sections, as a rule, a fine-grained structure was observed irrespective of T value.
Such samples had coarse grains and significant porosity.

In particular, the effect of grain size and matrix content were examined.
It is shown, by comparing with real micrographs, that the method captures the features of real microstructures in terms of grain size distribution and grain aspect ratio.
A number of authors [3, 4] have generated finite element meshes directly based on actual microstructural images.
The real microstructures have a higher percentage of small grains than its numerical counterpart due to small fragmented grains.
(a) 40% grains (b) 50% grains (c) 60% grains (d) 40% grains (e) 50% grains (f) 60% grains Figure 3: The Von-Mises equivalent strain distribution in the numerical microstructures with (a-c) 5×5 grains and (d-f) 10×10 grains subjected to a normal traction of 100 MPa.

The processing routes exert a strong influence on the development of the ultra-fine grain structure [5,6,10-12].
rationalized the effect of the processing route in terms of crystallography; when a billet was rotated in order for a slip plane to be inclined close to the grain elongation direction or theoretical shear plane, the grain fragmentation was promoted [13].
Slip pattern analysis suggested that a large number of slip systems were activated, resulting in the formation of deformation bands as observed macroscopically.
In route A, however, microstructures are still layered structures with dislocation boundaries closely parallel to the grain elongation direction, while those in route Bc are more equiaxed structures with grain diameter less than 500 nm.
It is suggested that these heterogeneous structure might promote the grain refinement in the subsequent passes.