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.

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

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.

Morphology and atomic structure of segregated grain boundaries in Cu-Sb

1992 ◽  
Vol 50 (1) ◽  
pp. 254-255
Author(s):  
R. W. Fonda ◽  
D. E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Atomic Structure ◽  
Copper Alloys ◽  
Polycrystalline Materials ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The properties of polycrystalline materials are strongly dependant upon the strength of internal boundaries. Segregation of solute to the grain boundaries can adversely affect this strength. In copper alloys, segregation of either bismuth or antimony to the grain boundary will embrittle the alloy by facilitating intergranular fracture. Very small quantities of bismuth in copper have long been known to cause severe grain boundary embrittlement of the alloy. The effect of antimony is much less pronounced and is observed primarily at lower temperatures. Even though moderate amounts of antimony are fully soluble in copper, concentrations down to 0.14% can cause grain boundary embrittlement.

Degradation of the Strength of a Grain and a Grain Boundary due to the Accumulation of the Structural Defects of Crystal

2018 ◽  
Author(s):  
Guoxiong Zheng ◽  
Yifan Luo ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Grain Boundary ◽  
Tensile Test ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Semiconductor Devices ◽  
Ebsd Analysis ◽  
Structural Defects ◽  
Polycrystalline Materials ◽  
Transgranular Fracture

Various brittle fractures have been found to occur at grain boundaries in polycrystalline materials. In thin film interconnections used for semiconductor devices, open failures caused by electro- and strain-induced migrations have been found to be dominated by porous random grain boundaries that consist of a lot of defects. Therefore, it is very important to explicate the dominant factors of the strength of a grain boundary in polycrystalline materials for assuring the safe and reliable operation of various products. In this study, both electron back-scatter diffraction (EBSD) analysis and a micro tensile test in a scanning electron microscope was applied to copper thin film which is used for interconnection of semiconductor devices in order to clarify the relationship between the strength and the crystallinity of a grain and a grain boundary quantitatively. Image quality (IQ) value obtained from the EBSD analysis, which indicates the average sharpness of the diffraction pattern (Kikuchi pattern) was applied to the crystallinity analysis. This IQ value indicates the total density of defects such as vacancies, dislocations, impurities, and local strain, in other words, the order of atom arrangement in the observed area in nano-scale. In the micro tensile test system, stress-strain curves of a single crystal specimen and a bicrystal specimen was measured quantitatively. Both transgranular and intergranular fracture modes were observed in the tested specimens with different IQ values. Based to the results of these experiments, it was found that there is the critical IQ value at which the fracture mode of the bicrystal specimen changes from brittle intergranular fracture at a grain boundary to ductile transgranular fracture in a grain. The strength of a grain boundary increases monotonically with IQ value because of the increase in the total number of rigid atomic bonding. On the other hand, the strength of a grain decreases monotonically with the increase of IQ value because the increase in the order of atom arrangement accelerates the movement of dislocations. Finally, it was clarified that the strength of a grain boundary and a grain changes drastically as a strong function of their crystallinity.

The Influence of the Exterior Surface on Grain Boundary Mobility Measurements

2014 ◽  
Vol 95 ◽  
pp. 56-65
Author(s):  
Amy Novick-Cohen ◽  
Anna Zigelman ◽  
Arkady Vilenkin
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Mean Curvature ◽  
Boundary Energy ◽  
Polycrystalline Materials ◽  
Normal Velocity ◽  
Exterior Surface ◽  
Mean Curvature Motion ◽  
Curvature Motion ◽  
Half Loop

Polycrystalline materials typically contain a very large number of grains whose surrounding grain boundaries evolve over time to reducethe overall energy of the microstructure. The evolution of the microstructure is influencedby the motion of the exterior surface since the grain boundaries couple to the exterior surface of the specimen; these effects can be appreciable especially in thin specimens. We model these effects using the classical framework of Mullins, in whichgrain boundaries move by mean curvature motion, Vn =A κ, and the exterior surface evolves by surface diffusion, Vn = -BΔs κ. Here Vn and κ denote the normal velocity and the mean curvature of the respective evolving surfaces, and Δs is the surface Laplacian. A classical way to determine A, the ``reduced mobility," is to make measurements based on the half-loop bicrystalline geometry. In this geometry one of the two grains, which embedded within the other, recedes at a roughly constant rate which can provide an estimate for A. In this note, we report on findings concerning the effects of the exterior surface on grain boundary motion and mobility measurements in the context of the half-loop bicrystalline geometry. We assume that the ratio of grain boundary energy to the exterior surface energy is small, and suitable assumptions are made of the specimen aspect ratio.

Anisotropic Behaviour of Grain Boundaries

2005 ◽  
Vol 482 ◽  
pp. 63-70 ◽  
Author(s):  
Václav Paidar ◽  
Pavel Lejček
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
Grain Boundary Engineering ◽  
Interfacial Dislocation ◽  
Special Character ◽  
Boundary Properties ◽  
Properties Of Materials ◽  
Boundary Classification ◽  
Boundary Chemistry

Grain boundaries are decisive for many properties of materials. Due to short-range stress field their influence is primarily based on their atomic structure. Special character of grain boundary properties related to their structure, follows from the nature of atomic arrangements in the boundary cores, from the interfacial dislocation content and from the boundary mobility. All those aspects of boundary behaviour are strongly influenced by the boundary chemistry including various segregation phenomena. Approaches to the boundary classification and the interpretation of recent experimental results are discussed in the context of the complex relationship between microstructure and material properties. Such findings are essential for Grain Boundary Engineering proposed to improve the performance of polycrystalline materials.

scholarly journals Towards Understanding the Different Influences of Grain Boundaries on Ion Transport in Sulfide and Oxide Solid Electrolytes

2019 ◽  
Author(s):  
James Dawson ◽  
Pieremanuele Canepa ◽  
Matthew Clarke ◽  
Theodosios Famprikis ◽  
Dibyajyoti Ghosh ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Ion Transport ◽  
Grain Boundaries ◽  
Solid Electrolytes ◽  
Ionic Conductivities ◽  
Liquid Electrolyte ◽  
Boundary Resistance ◽  
Polycrystalline Materials ◽  
Solid State Batteries ◽  
And Performance

Solid electrolytes provide a route to the development of all-solid-state batteries that can potentially surpass the safety and performance of conventional liquid electrolyte-based devices. Sulfide solid electrolytes have received particular attention as a result of their high ionic conductivities. One of the main reasons for such high ionic conductivity is the apparently reduced grain boundary resistance of sulfide solid electrolytes compared to their oxide counterparts, but this is not fully established. Using two model electrolyte systems, Na3PS4 and Na3PO4, we apply a novel microscale simulation approach to analyze ionic transport in polycrystalline materials with various grain volumes. For Na3PO4, high grain boundary resistance is found, with the Na-ion conductivity decreasing with decreasing grain volume. For Na3PS4, the overall influence of grain boundaries is significantly reduced compared to the oxide. Detailed analysis reveals a minimal change in the local structures and Na-ion conduction mechanism between bulk and polycrystalline Na3PS4, whereas the change is far more substantial for Na3PO4, with evidence of over-coordination of Na ions at the grain boundaries. Our microscale approach helps to explain the fundamentally different influences of grain boundaries on ion transport in phosphate and thiophosphate solid electrolytes.

Cation Coordination At Σ Grain Boundaries in TiO2 and SrTiO3, and its Effect on the Local Electronic Properties

1999 ◽  
Vol 5 (S2) ◽  
pp. 792-793
Author(s):  
J.A. Zaborac ◽  
J.P. Buban ◽  
H.O. Moltaji ◽  
S. Stemmer ◽  
N.D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Electronic Properties ◽  
Defect Formation ◽  
Boundary Structure ◽  
Polycrystalline Materials ◽  
Dominant Effect ◽  
Grain Boundary Structure ◽  
Charge Potential ◽  
Cation Coordination

Grain boundaries have long been known to have a dominant effect on the electronic properties of polycrystalline materials. In the case of electroceramic oxides, the thermodynamics of defect formation (vacancies or interstitials, cations or anions) are usually invoked to predict the presence of a space charge potential at the grain boundaries. The relative energetics for the formation of each type of defect determines the size and sign of this potential barrier and thus, the effect that boundaries have on the overall electronic properties of the materials. However, a limitation to this continuum thermodynamics approach is that it does not consider the effect of the grain boundary structure.To investigate whether the grain boundary atomic structure can have an effect on the energetics of defect formation and hence the electronic properties, here we examine the structure of Σ5 boundaries in two systems, SrTiO3 (perovskite) and TiO2(rutile).

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.

Evidence from in situ TEM straining studies for the mechanism of transfer of slip across a grain boundary

1988 ◽  
Vol 46 ◽  
pp. 616-617
Author(s):  
I.M. Robertson ◽  
T.C. Lee ◽  
P. Rozenak ◽  
G.M. Bond ◽  
H.K. Birnbaum
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Transfer Process ◽  
Boundary Structure ◽  
In Situ Tem ◽  
Boundary Dislocation ◽  
Dislocation Source ◽  
Structure Changes ◽  
Matrix Dislocation

The bulk mechanical properties of a material will primarily be determined by the integrity of the grain boundaries which depends on the local chemistry and the boundary structure. Changes in the composition of the boundary may affect the strength of the atomic bonds through a redistribution of the electrons; this effect has been predicted from theoretical calculations1 but not determined experimentally. The structure of the boundary will be determined by the mismatch between the adjoining grains and it will affect the mechanism by which strain is transferred through the boundary. From static observations of the interaction between matrix and grainboundary dislocations the following scenario has been constructed for the transfer process through random boundaries; The interaction between the incoming matrix dislocation and those in the grain boundary cause the emission of a dislocation from a grain-boundary dislocation source into the adjacent grain. To preserve the contiguity of the grain boundary a residual dislocation will be created within the grain boundary.

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