The influence of grain boundary ledge density on the flow stress in nickel

1978 ◽  
Vol 33 (1) ◽  
pp. 69-80 ◽  
Author(s):  
Eswarahalli S. Venkatesh ◽  
Lawrence E. Murr
Keyword(s):  
Flow Stress ◽  
Grain Boundary ◽  
Ledge Density ◽  
Boundary Ledge

Effect of Grain Boundary Ledges on the Flow Stress in Nickel

1977 ◽  
Vol 35 ◽  
pp. 284-285
Author(s):  
Eswarahalli S. Venkatesh ◽  
L.E. Murr
Keyword(s):  
Flow Stress ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
Structure And Properties ◽  
Boundary Dislocation ◽  
Dislocation Source ◽  
Type Relation ◽  
Ledge Density ◽  
Boundary Ledge

In a recent paper1 it was shown that grain boundary ledge structure can be changed by appropriate thermomechanical treatments. Grain boundary ledges are sources of dislocations2. Recently the effects of grain boundaries on the mechanical properties in metals and alloys were studied3,4. For a few years now the structure and properties of grain boundaries and their control have been considered as a means of strengthening polycrystalline materials5,6. Li5 has derived a Hall-Petch type relation in terms of grain boundary dislocation source (ledge) density, m, in the form where L is the grain size, σ0 and α are constants, and G ana b have the usual meaning. The influence of grain boundary ledge density, on the flow stress is considered in this paper.In the present work, pure (99.98%) nickel sheet mill rolled (hot) to 0.022 in. thick was used.

Hardening effects of grain boundary defect structure

1978 ◽  
Vol 36 (1) ◽  
pp. 430-431
Author(s):  
Eswarahalli S. Venkatesh ◽  
L.E. Murr
Keyword(s):  
Grain Boundary ◽  
Defect Structure ◽  
Structural Features ◽  
Metals And Alloys ◽  
Thermal Treatments ◽  
Dislocation Source ◽  
Boundary Defect ◽  
Ledge Density ◽  
Hot Rolled ◽  
Boundary Ledge

The grain boundary defect structure can be changed to advantage by appropriate mechanical and thermal treatments. Researchers continue to show interest in understanding the effects of boundary defect structure on the mechanical properties of polycrystalline metals and alloys. Grain boundary structural features such as boundary ledges have been considered as a means of strengthening in metals and alloys. Considering the various models of Hall-Petch analyses, the grain boundary strength, σg can be expressed as σg = 8αGb(l-υ)m(L/ℓ); where m is the grain boundary ledge density, L is the grain size, ℓ is the distance of dislocation source in the adjacent grain matrix from the boundary, and G, b, and υ have the usual meaning. In particular, the influence of grain boundary ledge density on the strength (hardness) of grain boundaries is considered in the present paper.In the present investigation, pure (99.98%) nickel sheet mill (hot) rolled to 0.022 in. thick was used.

Metallurgical Effects of Grain Boundary Ledges

1977 ◽  
Vol 35 ◽  
pp. 126-129
Author(s):  
L.E. Murr
Keyword(s):  
Grain Boundary ◽  
Quantitative Data ◽  
Mechanical Treatment ◽  
Unit Length ◽  
Physical And Mechanical Properties ◽  
Direct Observations ◽  
Transmission Electron ◽  
Properties Of Materials ◽  
Thermo Mechanical Treatment ◽  
Ledge Density

Ledges in grain boundaries can be identified by their characteristic contrast features (straight, black-white lines) distinct from those of lattice dislocations, for example1,2 [see Fig. 1(a) and (b)]. Simple contrast rules as pointed out by Murr and Venkatesh2, can be established so that ledges may be recognized with come confidence, and the number of ledges per unit length of grain boundary (referred to as the ledge density, m) measured by direct observations in the transmission electron microscope. Such measurements can then give rise to quantitative data which can be used to provide evidence for the influence of ledges on the physical and mechanical properties of materials.It has been shown that ledge density can be systematically altered in some metals by thermo-mechanical treatment3,4.

A Numerical and Experimental Study of Cavitation in a Hot Tensile Axisymmetric Testpiece

2005 ◽  
Vol 40 (6) ◽  
pp. 571-586 ◽  
Author(s):  
Y Liu ◽  
J Lin ◽  
T. A Dean ◽  
D. C. J Farrugia
Keyword(s):  
Experimental Study ◽  
Flow Stress ◽  
Grain Boundary ◽  
Thermal Gradient ◽  
Tensile Testing ◽  
Tensile Deformation ◽  
Strain Rates ◽  
Test Results ◽  
Integrated Technique ◽  
Hot Tensile Deformation

During axisymmetric hot tensile testing, necking normally takes place due to the thermal gradient and the accumulation of microdamage. This paper introduces an integrated technique to predict the damage and necking evolution behaviour. Firstly, a set of multiaxial mechanism-based unified viscoplastic-damage constitutive equations is presented. This equation set, which models the evolution of grain boundary (intragranular) and plasticity-induced (intergranular) damage, is determined for a free-cutting steel tested over a range of temperatures and strain rates on a Gleeble thermomechanical simulator. This model has been implemented using the CREEP subroutine of the commercial finite element (FE) solver ABAQUS. Numerical procedures to simulate axisymmetric hot tensile deformation are developed with consideration of the thermal gradient along the axis of the tensile testpiece. FE simulations are carried out to reproduce the necking phenomenon and the evolution of plasticity-induced and grain boundary damage. The simulated results have been validated with experimental tensile test results. The effects of necking and its associated stress state on flow stress and ductility are investigated. The flow stress and ductility data obtained from a Gleeble material simulator under various hot deformation conditions have also been numerically studied.

The plasticity and cleavage of polycrystalline beryllium II. The cleavage strength and ductility transition temperature

1980 ◽  
Vol 370 (1740) ◽  
pp. 29-39 ◽  
Keyword(s):  
Transition Temperature ◽  
Flow Stress ◽  
Grain Boundary ◽  
Stress Axis ◽  
Second Phase ◽  
Temperature Dependent ◽  
Second Phase Particles ◽  
Cleavage Strength ◽  
Dependent Flow ◽  
Strength And Ductility

For a grain diameter d, the cleavage strength is proportional to d -1/2 , but intercepts the stress axis. Initiation of cleavage in second phase particles of a size that varies suitably with d could produce this relation. More likely, the cleavage strength is determined by the condition for propagation of a microcrack across a grain boundary. An explanation of the stress intercept is given in terms of the probability that the critical microcrack size is an increasing multiple of d as the grains become finer. Directly measured ductility transition temperatures agree with those deduced from the intersection of a temperature dependent flow stress with a temperature independent cleavage strength.

Annealing Temperature and Grain Size Effect on the Grain Boundary Ledge (Density) Structure in Nickel

1977 ◽  
Vol 35 ◽  
pp. 286-287
Author(s):  
Eswarahalli Venkatesh
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Annealing Temperature ◽  
Grain Size Effect ◽  
Density Structure ◽  
Sheet Mill ◽  
Experimental Parameters ◽  
Boundary Ledge

In recent years many researchers have shown great interest in understanding the structure of grain boundaries1,2 and their influence on the mechanical properties of metals and alloys3-5. It has been shown that the structure of grain boundaries can be changed by appropriate thermomechanical treatments6. There are many experimental parameters that can influence the grain boundary ledge structure. The influence of annealing temperature and grain size are considered here.In the present work, pure (99.98%) nickel sheet mill rolled (hot) to 0.022 in. thick was used. One batch of sample was cut and rolled to 40% reduction in thickness and annealed at 800-1125°K in argon,and air cooled to achieve a constant grain size of 50 μm in all samples. A second set of samples was cut and rolled 10-70% reduction in thickness and similarly annealed at 800-1325°K so as to obtain different samples with grain size of 2, 30, 50, and 150 μm.

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