Search results

Polyhedron in shape was dominated with obvious large numbers of pores on the surface.
When temperature was increased to 1100 oC, less numbers of pores were found and no appreciable change in grain size and shape was visible in comparison with the 1000oC sample.
This indicated well-sintered pellets and high grain compact.
Up to present, a number of papers had reported the possible mechanism of abnormal grain growth and corresponding measures taken to control large grain growth were also suggested[6-8].
This was believed to be due to the abnormal grain growth.

However, perhaps the most important characteristic of the grain structure is the grain intensity λ (the more common notation in metallographic praxis is �V), namely the mean number of grains per unit volume or, equivalently, its reciprocal value - the mean grain volume Ev.
However, even this structure is not encountered in real polycrystals the grains of which grains are approximate irregular polyhedrons with number of faces about 14 and more; typically only three grains meet along a common edge and four grains meet in a common vertex.
The intercept intensity λ" (the mean number of grain chords or intercepts per unit length of the test lines) as estimated by profile count is then λ" = (s/4)λ.
In sections of normal tessellation is the mean number of vertices per profile 6 and in every vertex meet three profiles, so that the number of vertices PA can be estimated by 2�A.
For example, without changing appreciably the grain shape and volume and the mean number of grains per unit volume, the boundaries become wavy in such a way that their total area is doubled.

A number of examples are presented, including grain boundary segregation, precipitation of second-phase particles in a polycrystal, and interaction between segregation at a grain boundary and coherent precipitates inside grains.
For example, the left-hand side grain (Grain I) is ascribed a misorientation angle = with respect to a fixed reference, while an angle = q () is ascribed for the right-hand side grain (Grain II) in Fig. 1 (a).
Coherent precipitates inside grains and grain boundary segregation.
One was embedded in Grain I, while the other was embedded in Grain II.
Fig. 2 Coherent precipitates inside grains in different crystallographic orientations in the case of (a) bi-crystal (60o grain II), (b) bi-crystal (45o grain II), and (c) 4 grains system.

In order to obtain the diffractions from an enough number of grains, various types of oscillation methods, which were translation, rotation and tilting of the specimen, were examined.
The number of the grains, N, existing the radiation area, A, in the measurement of laboratory X-rays is given by 29767== S A N where d is 37 µm and A is 4×8 mm2.
As mentioned above, the luck of the number of diffracted grains is most likely the reason for these results.
With tilting oscillation, the number of diffracted grains does not increase much, but the diffracted grains change because the tilting oscillation can shift the normal vector from diffraction plane.
The solid squares, triangles and circles correspond to the translation distances of 1, 2 and 4 mm, and to the number of grains of 5322, 7182 and 10903, respectively.

The alloying of B or Ni to Cr reduces the grain size of the alloys.
terms of grain size effect.
The estimated volume fraction of grain boundaries increases from 3 vol% for 100 nm of the grain size to 30 vol% for 10 nm of the grain size.
The microhardness of Cr or Ti based alloys shows the maximum around 50at% elements, where the number of bonding of Cr or Ti and elements becomes maximum.
The microhardness of nanostructured Cr based alloys are controlled by the grain size, and also the structure of grain boundaries such as amorphous structure.

The granularity of diamond grains used was 60/70.
Furthermore, the total drilling hole number with the brazed and sintered core drill is 800 and 260, respectively, which means about 3 times in the life of the multi-layer brazed diamond core drill than in that of the sintered one.
Furthermore, the average total drilling hole number with the brazed and sintered core drills is 800 and 500, respectively.
But the grains quantity of the monolayer brazed diamond core drill with optimum grain distribution is only one-third of the multi-layer brazed Diamond grits Drag tails Drag tail Diamond Diamond pull-out cavities diamond core drill with random grain distribution, which means the utilization rate of diamond grain for monolayer brazed diamond core drill with optimum grain distribution is about 2 times than that of the multi-layer one with random grain distribution.
Table 3 Results of contrast machining performance evaluation Machining performance Multi-layer brazed diamond core drill with random grain distribution Monolayer brazed diamond core drill with optimum grain distribution Average spindle direction force［N］ 160 130 The total drilling hole number 800 500 Drilling hole number per diamond grit 2.6 5 Optimization Design of Multi-layer Brazed Diamond Tool Topography Considering that the absolute irregular distribution of grains is not a requirement of the grinding process, contrarily it will have a significant negative influence on the grinding process, our group put forward a new concept on the relatively regular and reasonable distribution of grains on the tool surface in accordance with different machining demands, and a creative idea of the optimization design of grinding tool topography in accordance with machining demands and grinding parameters as well as the optimization of grinding parameters

While the specimens pressed via route A showed lamellar grain shapes those via route C or BC exhibited equiaxed grains.
Variation of the texture strength in Zr702 as a function of number of passes in ECAP via different routes.
The other routes, i.e., C and BC, either alternate the intensity or slightly weaken it with the number of passes.
Although grain refining down to the level of 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 Maximum f(g) value Number of passes Route A Route BC Route C0.2µm can be obtained by A, C or BC alike, the equiaxed grain feature is promoted most efficiently by route BC, which is attributed to increased random high angle boundaries due to intersection of shear strain paths caused by rotation of specimens between each pass.
Moreover, the intensity of the main texture components is also affected by the route of deformation; the intensity for route A increases while that for route BC or C decreases with the number of passes.

that the accommodation process, i.e., the dislocation glide inside the grains, becomes more difficult with decreasing grain size in the nanometer grain size range, even though the grain boundary sliding as the major process becomes facilitated.
Thus, the reverse grain size dependence of superplastic elongation has been confirmed in the nanometer grain size range.
It should be noted that virtually no dislocation can be observed in the grains of the as-quenched specimen, while an appreciable number of dislocations are observed both in the α and β-phase grains of the aged specimen.
The m values of ultrafine-grained and normally fine-grained specimens were 0.38 and 0.48, respectively, which were chose to the theoretical values for the viscous dislocation glide inside the grain, 0.33, and the grain boundary sliding, 0.5.
The dislocation glide inside grain, the accommodation process, will rate-control the whole process in the ultrafine-grained specimen, while the grain boundary sliding, the main process, will be the rate-controlling in the normally fine-grained specimen.

Smith, Modelling radiation effects at grain boundaries in bcc iron, Nucl.
Smith, Preferential damage at symmetrical tilt grain boundaries in bcc iron, Nucl.
Horstemeyer, Probing grain boundary sink strength at the nanoscale: Energetics and length scales of vacancy and interstitial absorption by grain boundaries in α-Fe, Phys.
Uberuaga, Role of atomic structure on grain boundary-defect interactions in Cu, Phys.
Suzuki, Coupling grain boundary motion to shear deformation, Acta Mater. 54 (2006) 4953-4975

Based on the concept, we used CNTs directly as cutting grains for nano machining [4-7].
Grain Spacing L.
Based on VHigh (Eq. (1)), the grain spacing L (Fig. 2) can be obtained as L= (VHigh/ng) 1/3, (2) where ng is the grain number in the CNT wheel (Fig. 2).
In a single layer of a MWCNT, the number of carbon atoms nCi can be obtained as nCi=niCRnCA/nC-C=(AiCNT/ACR)nCA/nC-C=4πdilCNT/(33/2lC-C2), (4) where niCR is the number of carbon rings in a CNT layer, nCA is the number of carbon atoms in a carbon ring, nCA=6, nC-C is the number of C-C bonds for a carbon atom, nC-C=3, AiCNT is the area of the CNT layer i, AiCNT=πdilCNT, di is the diameter of the layer i, lCNT is the mean length of CNT (Table 1), ACR is the area of a carbon ring, ACR=33/2/2lC-C2, lC-C is the C-C bond length (Table 1).
An abrasive grain takes a circular path Ideal Actual Ideal Actual Ideal Actual 500 600 700 800 900 1000 1000 1250 1500 1750 2000 5 6 7 8 9 10 500 600 700 800 900 1000 60 70 80 90 1005 6 7 8 9 10 500 600 700 800 900 1000 80 85 90 95 1005 6 7 8 9 10 Mean length lCNT (nm) Mean outer diameter dCNT (nm) Mean layer number nLayer b - Feed of workpiece per cutting edge s (nm) a - Grain spacing L (nm) a b a b a b through the surface of a workpiece (Fig. 5).