Novel Nanostructured Metal and Ceramic Composites

2002 ◽  
Vol 750 ◽  
Author(s):  
J. Narayan
Keyword(s):  
Grain Size ◽  
Nanocrystalline Materials ◽  
Ceramic Composites ◽  
Interfacial Region ◽  
Uniform Size ◽  
Boundary Shear ◽  
Synthesis Procedure ◽  
And Control ◽  
Critical Grain Size ◽  
Nanostructured Metal

ABSTRACTWe have designed a unique synthesis procedure to create nonomaterials of uniform grain size and control the chemistry of interfaces between the grains. The metastability of nanocrystalline materials is a major challenge which can be addressed by controlling the chemistry of interfaces. The hardness of these films having a uniform size was measured as a function of grain size using a nanoindentation technique. It was found that hardness increased with decreasing grain size in accordance with Hall-Petch model. However, below a critical grain size we observed a decrease or softening with a further decrease in grain size. These observations in metals and ceramics are modeled in view of intragrain deformation (Hall-Petch regime) and intergrain deformation (grain boundary shear/sliding )in the softening regime. Since we can change the alloying of interfacial region, we can address the metastability as a function of temperature, which is crucial from applications viewpoint of these materials.

Mechanical Properties of Novel Nanocrystalline Materials

2001 ◽  
Author(s):  
J. Narayan ◽  
H. Wang ◽  
A. Kvit
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
High Surface ◽  
Grain Boundary Sliding ◽  
Boundary Shear ◽  
Functionally Gradient ◽  
Boundary Sliding ◽  
First Time ◽  
Critical Grain Size

Abstract We have synthesized nanocrystalline thin films of Cu, Zn, TiN, and WC having uniform grain size in the range of 5 to 100 nm. This was accomplished by introducing a couple of manolayers of materials with high surface and have a weak interaction with the substrate. The hardness measurements of these well-characterized specimens with controlled microstructures show that hardness initially increases with decreasing grain size following the well-known Hall-Petch relationship (H∝d−½). However, there is a critical grain size below which the hardness decreases with decreasing grain size. The experimental evidence for this softening of nanocrystalline materials at very small grain sizes (referred as reverse Hall-Petch effect) is presented for the first time. Most of the plastic deformation in our model is envisioned to be due to a large number of small “sliding events” associated with grain boundary shear or grain boundary sliding. This grain-size dependence of hardness can be used to create functionally gradient materials for improved adhesion and wear among other improved properties.

What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

2006 ◽  
Vol 976 ◽  
Author(s):  
Christopher Carlton ◽  
P. J. Ferreira
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Critical Value ◽  
Petch Relationship ◽  
And Diffusion ◽  
Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

Percolative composite model for prediction of the properties of nanocrystalline materials

1997 ◽  
Vol 12 (7) ◽  
pp. 1828-1836 ◽  
Author(s):  
Rachman Chaim
Keyword(s):  
Experimental Data ◽  
Grain Size ◽  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
Composite Model ◽  
Grain Sizes ◽  
Percolation Thresholds ◽  
Definition Of ◽  
Critical Grain Size ◽  
Transport Type

A physical percolating composite model is presented for description of the changes in the transport-type properties with grain size in nanocrystalline materials. The model is based on hierarchial percolation through the different microstructural components such as grain boundaries, triple lines, and quadruple nodes at grain sizes when their respective percolation thresholds are reached. The model yields critical grain sizes at which the properties may change significantly. These grain sizes depend on the grain boundary thickness. Master curves were calculated for the elastic modulus and compared to the experimental data from the literature. Better fit was found with the experimental data in comparison to Hill's approximation model. The critical grain size at grain boundary percolation threshold is suggested as a criterion for definition of materials to exhibit nanocrystalline properties.

scholarly journals Deformation Mechanisms of Toughening of Nanocrystalline Materials

2020 ◽  
Vol 7 ◽  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Nanocrystalline Materials ◽  
Lattice Dislocation ◽  
Deformation Mechanisms ◽  
Dislocation Slip ◽  
And Migration ◽  
Toughness Enhancement ◽  
Critical Grain Size ◽  
Nanocrystalline Solids

We provide a brief review of our recent studiesconcerning the effects of various mechanisms of plasticdeformation of nanocrystalline materials on their fracturetoughness. We consider both conventional deformationmechanisms, such as lattice dislocation slip, and the deformationmechanism pronounced mostly in nanocrystalline solids, such asgrain boundary (GB) sliding and migration. We demonstrate thatwith a decrease in grain size, the effect of conventional latticedislocation slip on fracture toughness enhancement significantlydecreases. At the same time, for nanocrystalline solids withsmallest grain size fracture toughness can be increased due to GBsliding and migration. This implies that a transition from latticedislocation-mediated toughening to GB-deformation-producedtoughening can occur at a critical grain size in nanocrystallinesolids.

scholarly journals Atomistic Simulation of Nanocrystalline Materials

1995 ◽  
Vol 400 ◽  
Author(s):  
D. Wolf ◽  
S. R. Phillpot ◽  
P. Keblinski
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Atomistic Simulation ◽  
Nanocrystalline Silicon ◽  
High Energy ◽  
Atomistic Simulations ◽  
Silicon Based ◽  
Critical Grain Size ◽  
Energy Argument

AbstractAtomistic simulations show that high-energy grain boundaries in nanocrystalline copper and nanocrystalline silicon are highly disordered. In the case of silicon the structures of the grain boundaries are essentially indistinguishable from that of bulk amorphous silicon. Based on a free-energy argument, we suggest that below a critical grain size nanocrystalline materials should be unstable with respect to the amorphous phase.

Critical grain size for dislocation storage and consequences for strain hardening of nanocrystalline materials

2010 ◽  
Vol 63 (5) ◽  
pp. 477-479 ◽  
Author(s):  
O. Bouaziz ◽  
Y. Estrin ◽  
Y. Bréchet ◽  
J.D. Embury
Keyword(s):  
Grain Size ◽  
Strain Hardening ◽  
Nanocrystalline Materials ◽  
Critical Grain Size

Grain size effects in nanocrystalline materials

1992 ◽  
Vol 7 (8) ◽  
pp. 2114-2118 ◽  
Author(s):  
C. Suryanarayana ◽  
D. Mukhopadhyay ◽  
S.N. Patankar ◽  
F.H. Froes
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Size Effects ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
High Hardness ◽  
Careful Analysis ◽  
Grain Sizes ◽  
Critical Grain Size ◽  
Very High

Nanocrystalline materials have a grain size of only a few nanometers and are expected to possess very high hardness and strength values. Even though the hardness/strength is expected to increase with a decrease in grain size, recent observations have indicated that the hardness increases in some cases and decreases in other cases. A careful analysis of the available results on the basis of existing models suggests that there is a critical grain size below which the triple junction volume fraction increases considerably over the grain boundary volume fraction and this is suggested to be responsible for the observed softening at small grain sizes.

Critical grain size to limit the hydrogen-induced ductility drop in a metastable austenitic steel

2015 ◽  
Vol 40 (33) ◽  
pp. 10697-10703 ◽  
Author(s):  
Arnaud Macadre ◽  
Nobuo Nakada ◽  
Toshihiro Tsuchiyama ◽  
Setsuo Takaki
Keyword(s):  
Grain Size ◽  
Austenitic Steel ◽  
Metastable Austenitic Steel ◽  
Critical Grain Size
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