Structure and Grain Boundaries of Ultrafine-Grained Nickel after Rolling and Forging at Cryogenic Temperature

2021 ◽  
Vol 313 ◽  
pp. 31-40
Author(s):  
Evgeny V. Naydenkin ◽  
Ivan P. Mishin
Keyword(s):  
Grain Boundaries ◽  
Cryogenic Temperature ◽  
Liquid Nitrogen Temperature ◽  
Deformation Bands ◽  
Localized Deformation ◽  
Twin Boundaries ◽  
Fragmented Structure ◽  
Ultrafine Grained ◽  
Annealing Twins ◽  
Small Grains

The structure and misorientations of grain boundaries of ultrafine-grained nickel subjected to rolling and forging at liquid nitrogen temperature are studied. It is shown that as a result of rolling in UFG nickel obtained by the ECAP the forming of a band fragmented structure with the formation of special twin boundaries Σ3 is observed. An increase in the strain rate (forging) leads to the appearance of localized deformation bands in which the formation of new small grains is observed through dynamic recrystallization. The development of recrystallization results in increase up to 7% in UFG nickel the fraction of special twin boundaries Σ3 which are similar in nature to annealing twins.

Some comparative observations of carbide precipitation morphology related to coherent twin boundaries and high-energy grain boundaries in stainless steels

1993 ◽  
Vol 51 ◽  
pp. 1166-1167
Author(s):  
R. J. Romero ◽  
E. A. Trillo ◽  
A. H. Advani ◽  
L. E. Murr ◽  
W. W. Fisher
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
High Energy ◽  
Carbide Precipitation ◽  
304 Stainless Steel ◽  
Twin Boundaries ◽  
Transmission Electron ◽  
Wide Range ◽  
Annealing Twins ◽  
Precipitation Morphology

Stickler and Vinckier showed more than three decades ago that there is a very consistent relationship between the boundaries upon which carbides (M23 C6) precipitate in 300 series stainless steels (having carbon contents ranging from 0.02 to 0.08 wt%). For example, carbides first appear on regular (high-energy) grain boundaries, then non-coherent boundaries and steps on annealing twins, and finally on coherent twin boundaries at a constant temperature above about 600° C, and at aging times which, correspondingly, change by orders of magnitude (1,10, 100 hrs. respectively at 675°C for 304 stainless steel). We have examined a wide range of precipitation features on these various boundaries in 316 and 304 stainless steels which have not been described previously because there have been limited observations comparing carbide morphologies in the transmission electron microscope (TEM) for high-energy grain boundaries (γgb ∼ 800 mJ/m2), non-coherent steps on twin boundaries (γTB ∼ 200 mJ/m2), and coherent twin boundaries (γtb ∼ 20 mJ/m2) for 316 and 304 stainless steels.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels

1992 ◽  
Vol 50 (2) ◽  
pp. 1216-1217
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Interfacial Free Energy ◽  
Carbide Precipitation ◽  
Twin Boundaries ◽  
Invariant Structure ◽  
Heat Treated ◽  
Constant Structure ◽  
Cr Depletion

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.

scholarly journals Image Simulations of Ge Twin Boundaries.

1992 ◽  
Vol 295 ◽  
Author(s):  
Stuart Mckernan ◽  
C. Barry Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Angle ◽  
Structural Units ◽  
Twin Boundaries ◽  
Large Unit ◽  
Unit Cells ◽  
The Individual ◽  
Image Simulations

AbstractGeneral high-angle tilt grain boundaries may be described by an arrangement of repeating structural units. Some grain-boundary defects may also be modeled by the incorporation of structural units of related boundary structures into the boundary. The simulation of these structures requires the use of prohibitively large unit cells. The possibility of modeling these boundaries by the superposition of image simulations of the individual structural units isinvestigated.

scholarly journals Annealing effect on microstructure and mechanical properties of Cu-Al alloy subjected to Cryo-ECAP

2018 ◽  
Vol 8 (1) ◽  
pp. 377-381
Author(s):  
Kun Xia Wei ◽  
Sheng Long Wang ◽  
Wei Wei ◽  
Qing Bo Du ◽  
Igor V. Alexandrov ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cryogenic Temperature ◽  
Uniform Elongation ◽  
Annealing Effect ◽  
Al Alloy ◽  
Angular Pressing ◽  
Microstructure And Mechanical Properties ◽  
Annealing Twins ◽  
Before And After ◽  
Liquid Nitrogen Cooling

Abstract Cu-7%Al alloy subjected to equal channel angular pressing at cryogenic temperature with liquid nitrogen cooling (Cryo-ECAP)was treated by annealing. The microstructure and mechanical properties of Cu-7%Al alloy before and after annealing were investigated. It shows that a large number of annealing twins formed in Cu-7%Al alloy subjected to Cryo-ECAP. After 300∘C and 0.5 h annealing in Cu-7%Al alloy processed by Cryo-ECAP, tensile strength and uniform elongation was increased up to 644 MPa and 7.6% respectively. The enhanced mechanical properties of Cu-7%Al alloy after annealing is attributed to the high density nanoscale twins.

Mechanism of Stress-Driven Grain Boundary Migration in Nanotwinned Materials

2018 ◽  
Vol 55 (1) ◽  
pp. 21-25 ◽  
Author(s):  
N.V. Skiba
Keyword(s):  
Theoretical Model ◽  
Grain Boundary ◽  
Twin Boundary ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
High Angle ◽  
Twin Boundaries ◽  
Critical Stresses ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials

Abstract Stress-driven grain boundary (GB) migration in ultrafine-grained materials with nanotwinned structure is theoretically described. In the framework of the theoretical model, the stress-driven high-angle GB migration is accompanied by migration of twin boundaries which adjoin this GB. Energetic characteristics and critical stresses of the GB migration accompanied by the twin boundary migration are calculated.

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