Is There a Critical Size in Nano Grained Metals for Ductile to Brittle Transition?

2004 ◽  
Author(s):  
Aman Haque ◽  
Taher Saif
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Critical Size ◽  
Volume Ratio ◽  
Metal Films ◽  
Metal Structures ◽  
Brittle Transition ◽  
Ductile To Brittle Transition ◽  
Metal Properties

Nanoscale metal films and electrodes are extensively used in today’s micro and nano electronics as well as nano mechanical systems. These metal structures are usually polycrystalline in nature with nano scale grains connected to each other by grain boundaries. The small size offers large grain boundary to volume ratio that is likely to affect the metal properties significantly. Here, we discuss the role of grain size and boundaries in determining the mechanical behavior of metals, such as elasticity and yielding.

A Re-Appraisal of Cavity Growth Processes in Superplasticity

1990 ◽  
Vol 196 ◽  
Author(s):  
Yan Ma ◽  
Terence G. Langdon
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Diffusion Process ◽  
Superplastic Deformation ◽  
Cavity Growth ◽  
Normal Model ◽  
Experimental Conditions ◽  
Diffusion Growth ◽  
New Model

ABSTRACTIt is well known that cavities are nucleated and grow during the superplastic deformation of many materials. The various theories for cavity growth are examined with special emphasis on the role of growth by diffusion. It is demonstrated that the normal model for the diffusion growth of cavities is inadequate for superplastic materials when the grain boundary lengths are very small. By developing a new model for the growth of an isolated cavity to sizes exceeding the grain size, it is shown that the diffusion process may play a major role in cavity growth under a range of experimental conditions.

The Effect of Intermetallic Phases on Ductile to Brittle Transition of Aluminium-Iron Alloy

2014 ◽  
Vol 592-594 ◽  
pp. 770-775
Author(s):  
Shahrukh Shamim ◽  
Gaurav Sharma ◽  
Chandrabalan Sasikumar
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Transition Temperature ◽  
Research Work ◽  
Iron Alloy ◽  
Energy Transition ◽  
Intermetallic Phases ◽  
Impact Testing ◽  
Brittle Transition ◽  
Ductile To Brittle Transition

The effect of intermetallic phases and grain size on ductile to brittle transition temperature of Aluminium-Iron alloy (Al–11% Fe) was investigated in this research work. An Izod impact testing method was adopted to study the DBTT in the temperature interval of 77 K to 373 K. The ductile-brittle transition points: fracture transition plastic (FTP), fracture-appearance transition temperature (FATT), impact energy transition temperature (IETT), fractional surface area of cleavage (brittle) and fibrous (ductile) fractures and grain size of the samples were also determined. The fracture toughness of Al-Fe alloy found decreasing with temperature in contrast to conventional materials. The fractographic investigation revealed that the microstructural changes play a major role in determining the fracture toughness of these alloys. Annealing of these samples slightly improved the fracture toughness as the spherical morphology of intermetallic particles resists the crack propagation.

Novel Nanocrystalline Composites

2002 ◽  
Author(s):  
J. Narayan
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Tungsten Carbide ◽  
Nickel Aluminide ◽  
Processing Technique ◽  
High Temperature Strength ◽  
Softening Behavior ◽  
Boundary Shear ◽  
Nanocrystalline Composites

We have developed a novel processing technique to fabricate tungsten carbide (WC) nanocomposites with uniform grain size. In this method, pulsed laser deposition of WC in conjunction with a few monolayers of nickel aluminide (NiAl) is used to control the grain size of nanocrystalline composites. The grain size of WC was controlled by the thickness of tungsten carbide and the substrate temperature. The role of NiAl is to ensure the nucleation of tungsten carbide islands, and it is relatively insoluble in WC. Using this approach, we have fabricated nanocomposites of grain sizes ranging from 6 nm to 35 nm. The hardness of the composite increases with the decrease in grain size, following approximately Hall-Petch relationship. Below a critical value, we observed a softening behavior which has been modeled to be related to intragrain deformation or grain boundary shear. The role of NiAl in grain boundary deformation is of particular interest in strengthening and stabilizing against the grain growth of nanocrystalline composites. The new WC-NiAl composite is expected to have superior high-temperature strength compared to conventional microcrystalline WC-Co composites.

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