Segregation-induced ordered superstructures at general grain boundaries in a nickel-bismuth alloy

Science ◽  
2017 ◽  
Vol 358 (6359) ◽  
pp. 97-101 ◽  
Author(s):  
Zhiyang Yu ◽  
Patrick R. Cantwell ◽  
Qin Gao ◽  
Denise Yin ◽  
Yuanyao Zhang ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Solute Segregation ◽  
Alloying Elements ◽  
High Symmetry ◽  
Polycrystalline Nickel ◽  
Lattice Matching ◽  
Properties Of Materials ◽  
Engineering Alloys ◽  
Bismuth Alloy

The properties of materials change, sometimes catastrophically, as alloying elements and impurities accumulate preferentially at grain boundaries. Studies of bicrystals show that regular atomic patterns often arise as a result of this solute segregation at high-symmetry boundaries, but it is not known whether superstructures exist at general grain boundaries in polycrystals. In bismuth-doped polycrystalline nickel, we found that ordered, segregation-induced grain boundary superstructures occur at randomly selected general grain boundaries, and that these reconstructions are driven by the orientation of the terminating grain surfaces rather than by lattice matching between grains. This discovery shows that adsorbate-induced superstructures are not limited to special grain boundaries but may exist at a variety of general grain boundaries, and hence they can affect the performance of polycrystalline engineering alloys.

Effects of Alloying Elements on Iron Grain Boundary Cohesion

1997 ◽  
Vol 492 ◽  
Author(s):  
X. Chen ◽  
D. E. Ellis ◽  
G. B. Olson
Keyword(s):  
Molecular Dynamics ◽  
Free Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
First Principles ◽  
Electronic Structure Calculations ◽  
Alloying Elements ◽  
Alloying Element ◽  
Long Time ◽  
Structure Calculations

For a long time, understanding the mechanisms of impurity-promoted embrittlement in iron and the consequent cohesion(decohesion) effects has been a challenge for materials scientists. The role alloying elements play in impurity-promoted embrittlement is important due to either their direct intergranular cohesion(decohesion) effects or effects upon embrittling potency of other impurities. Some alloying elements like Pd and Mo are known to be helpful for intergranular cohesion in iron and some other alloying elements like Mn are known to segregate to and weaken iron grain boundaries dramatically[1]. There have been intensive investigations on these mechanisms for a long time and especially, with the progress in computing techniques in recent years, calculations on more realistic models have become possible[2–4]. In this paper we briefly present our studies on some selected alloying-element/iron grain boundaries(GB) and free surface(FS) systems. The effects of Pd, Mo, Mn and Cr on the Fe Σ5 (031) grain boundary and its corresponding (031) free surface are examined, using a combination of molecular dynamics(MD) and first-principles electronic structure calculations. Section 2 gives a brief introduction to the methods used and Section 3 gives the main results.

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.

Effects of Impurities And Alloying Elements on Iron Grain Boundary Cohesion

1997 ◽  
Vol 475 ◽  
Author(s):  
D.E. Ellis ◽  
X. Chen ◽  
G.B. Olson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Physical And Mechanical Properties ◽  
Alloying Elements ◽  
Metallic Materials ◽  
Crucial Importance ◽  
Intergranular Embrittlement ◽  
Long Time ◽  
Impurity Doped ◽  
Segregation Of Impurities

In metallic materials, where grain boundaries(GB) are of crucial importance, impurities and alloying elements play an important role in determining their physical and mechanical properties because the behavior of a grain boundary may change drastically with the presence of impurities and alloying elements. For example, in iron and its alloys, including industrially important steels, the intergranular embrittlement is usually associated with segregation of impurities, like P and S, toward the GBs. On the other hand, alloying elements, like Mo and Pd, are helpful for intergranular cohesion in iron, due to either direct cohesion effect or effect upon embrittling potency of other impurities. Understanding the mechanisms of impurity-promoted embrittlement and the consequent cohesion(decohesion) effects is becoming more and more important and remains as a challenge for materials scientists. There have been intensive investigations on these mechanisms for a long time and with the progress in computing techniques in recent years, calculations on more realistic representations of impurity-doped grain boundaries have become possible[1–4].

scholarly journals Detection of Solute Segregation at Grain Boundaries

1980 ◽  
Vol 38 ◽  
pp. 360-361
Author(s):  
J. Briceno-Valero ◽  
R. Gronsky
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Solute Concentration ◽  
Boundary Region ◽  
Solute Segregation ◽  
Spectroscopic Techniques ◽  
Concentration Gradients ◽  
X Ray ◽  
Grain Boundary Plane

Studies of grain boundary segregation in metallurgical systems are traditionally based upon the premise that grain boundaries are more likely sites for solute atoms than their surrounding grains. This idea is manifested in experimnental studies which distinguish the solute concentration at boundaries from that of grain interiors using various spectroscopic techniques, including more recently, energy dispersive X-ray analysis in TEM/STEM instruments. A typical study therefore usually consists of spot or line scans across a grain boundary plane in order to detect concentration gradients at the boundary region. It has also been pointed out that there are rather severe problems in quantitatively determining the absolute solute concentration within the grain boundary, and data correction schemes for this situation have been proposed.

A new approach to atomic level characterization of grain boundaries by atom probe tomography

2014 ◽  
Vol 1645 ◽  
Author(s):  
L. Yao ◽  
M. K. Miller
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atom Probe Tomography ◽  
Ion Irradiation ◽  
Atom Probe ◽  
Heavy Ion ◽  
Solute Segregation ◽  
Full Description ◽  
High Dose ◽  
Ferritic Alloy

ABSTRACTA novel atom probe tomography (APT) method has been developed that enables a full description of the orientation relationship between individual grains to be determined together with estimates of the extents of solute segregation for all elements over the surface of the grain boundary with 1 nm by 1 nm spatial resolution. This approach also enables variations in the solute excess for the elements with the habit plane and curvature of the grain boundary to be evaluated. The method has been applied to a mechanically-alloyed nanostructured ferritic alloy (NFA) after high dose heavy ion irradiation. The innovative high-resolution two-dimensional mapping of the solute segregation across the surface of grain boundaries in the NFA clearly demonstrates that the distributions of chromium and tungsten are not uniform across the grain boundaries, and the distributions correlate with changes in its local curvature and the position of the grain boundary precipitates. These features pin the grain boundary against grain growth and provide the stability for excellent creep properties.

Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals

1997 ◽  
Vol 492 ◽  
Author(s):  
C. Elsässer ◽  
O. Beck ◽  
T. Ochs ◽  
B. Meyer
Keyword(s):  
Transition Metals ◽  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Density Functional ◽  
Local Density ◽  
High Symmetry ◽  
Many Body ◽  
Local Density Functional Theory ◽  
Symmetrical Tilt

ABSTRACTAtomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.

Grain Boundary Structural Transformations Induced by Solute Segregation

1984 ◽  
Vol 41 ◽  
Author(s):  
K. Sickafus ◽  
S. L. Sass
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Changes ◽  
Temper Embrittlement ◽  
Analytical Techniques ◽  
Major Change ◽  
Solute Segregation ◽  
Boundary Structure ◽  
Low Alloy Steels ◽  
Fracture Surfaces

AbstractThe problem of solute segregation came to prominence with relation to studies of the temper embrittlement of low alloy steels. McLean and Northcott1(1948) first suggested that segregation of various elements to the grain boundaries was primarily responsible for the intergranular fracture observed in steels susceptible to this embrittlement. Direct evidence for segregation came much later with the development of surface sensitive analytical techniques, especially Auger electron spectroscopy (AES). Using AES, it was determined that impurity elements such as P, Sb and Sn, as well as alloying elements such as Ni and Cr, were highly concentrated at the fracture surfaces in embrittled steels2. It is not clear, however, why solute segregation changes the mechanical strength of the grain boundaries in these materials. Based on recent calculations, Messmer and Briant3 proposed that certain solute species at a grain boundary change the chemical bonding at the interface. However, other more dramatic structural rearrangements may be possible upon segregation. Such structural changes were first suggested by the observation of facetted fracture surfaces in tellurium-doped iron alloys4. In the study presented here, it is shown that low concentrations of solute can cause changes in grain boundary structure. In particular, small concentrations of Au solute were found to cause a major change in the dislocation structure of low angle [001] Fe twist boundaries. Preliminary observations on the str ucture of a Fe-0.18 at.% Au* twist boundary were presented elsewhere5. Additional results will be presented here on the effect of changes in solute concentration and misorientation angle, θ, on this structural transformation. It is believed that these observations are evidence for the occurrence of a two-dimensional phase transformation in the grain boundary, similar to that predicted by Hart6

High-resolution STEM study of grain boundaries in high-Tc superconducting YBa2Cu3O7-x thin films

1989 ◽  
Vol 47 ◽  
pp. 174-175
Author(s):  
D. H. Shin ◽  
J. Silcox ◽  
D. K. Lathrop ◽  
S. E. Russek ◽  
R. A. Buhrman
Keyword(s):  
Thin Films ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Superconducting Film ◽  
High Tc ◽  
Lattice Matching ◽  
Axis Parallel ◽  
Lattice Images ◽  
Mgo Substrate

The grain boundary structures of high Tc superconducting YBa2Cu3O7-x thin films grown on yttrium-stabilized zirconia and MgO have been studied using a VG-HB501A STEM operating at 100 keV (bright field, Cs=1.l mm, αobj=12 mrad,θcol=4 mrad). In Fig. 1, lattice images of various types of grain boundaries of a superconducting film grown on MgO by low-temperature (660 °C) in situ sputtering are shown. This sample has a critical current density of ∼5 × 106 amp/cm2 at 4 K and a somewhat depressed transition temperature near 70 K possibly due to ion bombardment during the sputtering process and oxygen deficiencies. Beyond a few atomic distances most of the grain boundaries are clean and coherent.Since each grain in the film can take any of the possible orientations satisfying substrate-film lattice matching (along [100], [110], and [120] of the substrate, with either c-axis parallel or c-axis perpendicular, in the case of (100) MgO substrate), several different types of grain boundaries occur. Fig. 1(a) shows a grain boundary between two grains with c-axes in the plane of the substrate. Fig. 1(b), (c), and upper left area of (d) show grain boundaries between two grains, one with c-axis in the plane, and the other with c-axis perpendicular to the plane. At these grain boundaries c-axes are rotated through 90°.

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