Effects of Impurities And Alloying Elements on Iron Grain Boundary Cohesion

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].

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Effects of Alloying Elements on Iron Grain Boundary Cohesion

MRS Proceedings ◽

10.1557/proc-492-243 ◽

1997 ◽

Vol 492 ◽

Cited By ~ 1

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.

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The “Solidification” of Grain Boundaries with Increasing Temperature

MRS Proceedings ◽

10.1557/proc-357-337 ◽

1994 ◽

Vol 357 ◽

Cited By ~ 1

Author(s):

Witold Lojkowski ◽

Bogdan Palosz

Keyword(s):

Solid State ◽

Melting Point ◽

Grain Boundary ◽

Grain Boundaries ◽

High Temperatures ◽

Low Temperatures ◽

Melting Behavior ◽

Wetting Transitions ◽

Increasing Temperature ◽

Segregation Of Impurities

AbstractThe aim of the paper is to explain the recently observed de-wetting grain boundary transition with increasing temperature. On the example of a bicrystal from the Fe-6at.%Si alloy, it was found recently that as temperature is increased, the following GB transitions take place: “solid” (or regular) GB-→“premelted” GB →“solid” GB. At the same time the wetting/de-wetting transitions have taken place. Another example of such GB behavior was discovered during sintering of alumina. The inverse melting behavior is explained as follows: low melting point impurities cause GB premelting at low temperatures, However de-segregation of impurities at high temperatures causes return of the GB structure to its regular “solid” state.

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Influence of Grain Boundary Mobility on Microstructure Evolution during Recrystallisation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.715-716.191 ◽

2012 ◽

Vol 715-716 ◽

pp. 191-196

Author(s):

Myrjam Winning ◽

Dierk Raabe

Keyword(s):

Grain Boundary ◽

Cellular Automaton ◽

Grain Boundaries ◽

Single Crystals ◽

Microstructure Evolution ◽

Texture Evolution ◽

Three Dimensional ◽

Boundary Mobility ◽

Metallic Materials ◽

Grain Boundary Mobility

The paper introduces first investigations on how low angle grain boundaries can influence the recrystallisation behaviour of crystalline metallic materials. For this purpose a three-dimensional cellular automaton model was used. The approach in this study is to allow even low angle grain boundaries to move during recrystallisation. The effect of this non-zero mobility of low angle grain boundaries will be analysed for the recrystallisation of deformed Al single crystals with Cube orientation. It will be shown that low angle grain boundaries indeed influence the kinetics as well as the texture evolution of metallic materials during recrystallisation.

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STEM Investigation of Segregation and Local Structure at Grain Boundary in Tetragonal Zirconia

Microscopy and Microanalysis ◽

10.1017/s1431927600009636 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 549-550

Author(s):

H. Gu ◽

F. Wakai

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Solid Electrolytes ◽

Tetragonal Zirconia ◽

Boundary Structure ◽

Contrast Imaging ◽

Amorphous Films ◽

Grain Boundary Structure ◽

Z Contrast ◽

Segregation Of Impurities

Y or Ca stabilized tetragonal ZrO2 (TZP) exhibits superplasticity at high temperature, and can also be used as solid electrolytes. Those properties are dictated by structure and chemistry of grain boundaries, which can be controlled by segregation of impurities or additives. The grain boundaries were found either covered by amorphous films or free of the film. Co-segragation of additives and stabilizers has also been observed. To fully understand the correlation between segregation and grain boundary structure, a dedicated STEM (VG HB601) capable of EDX/EELS analysis and phase/Z-contrast imaging is employed to study 3Y-TZP doped with 0.3 and 0.9 mol% SiO2.Although Y-L lines arc dominated by overlapping Zr-L lines in EDX, Y excess at grain boundaries can still be measured by “spatial difference” which removes Zr signal with a spectrum from the bulk. The co-segregation of Si and Y is also observed (Fig. 1) at many boundaries. Their average excesses arc 5±2 nm−2and 25±10 run−2 respectively, close to 1 monolayer each of SiO2 and Y2O3.

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Investigations of the Bonding Changes Associated with Grain Boundary Embrittlement

MRS Proceedings ◽

10.1557/proc-458-93 ◽

1996 ◽

Vol 458 ◽

Author(s):

V. J. Keast ◽

J. Bruley ◽

D. B. Williams

Keyword(s):

Electronic Structure ◽

Grain Boundary ◽

Energy Loss ◽

Grain Boundaries ◽

Edge Structure ◽

Grain Boundary Embrittlement ◽

Impurity Elements ◽

Electron Energy Loss ◽

Segregation Of Impurities ◽

Boundary Embrittlement

ABSTRACTThe embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.

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

Science ◽

10.1126/science.aam8256 ◽

2017 ◽

Vol 358 (6359) ◽

pp. 97-101 ◽

Cited By ~ 66

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.

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Cooperative Chemical Rebonding In The Segregation Of Impurities In Silicon Grain Boundaries

MRS Proceedings ◽

10.1557/proc-442-213 ◽

1996 ◽

Vol 442 ◽

Author(s):

A. Maiti ◽

M. F. Chisholm ◽

S. J. Pennycook ◽

S. T. Pantelides

Keyword(s):

Grain Boundary ◽

Ab Initio ◽

Grain Boundaries ◽

Structural Transformation ◽

Atomic Resolution ◽

Segregation Energy ◽

Site Variation ◽

Segregation Of Impurities

AbstractWith ab initio calculations we show that the experimentally observed large segregation energies of As at Si grain boundaries can be explained by the formation of isolated dimers or ordered chains of dimers of threefold-coordinated As along the cores of grain boundary dislocations. We also find the intriguing possibility that As segregation may drive structural transformation of certain grain boundaries. Recently we have obtained the first atomic-resolution STEM images of As in a Si grain boundary, consistent with the formation of As dimers. Segregation energy of As dimers was found to be significantly higher in isolated dislocation cores, where larger site-variation in strain than in grain boundaries lead to further lowering of the electronic levels of As deep into the bandgap.

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Defect-Solute Interactions Near Irradiated Grain Boundaries

MRS Proceedings ◽

10.1557/proc-319-399 ◽

1993 ◽

Vol 319 ◽

Author(s):

E. P. Simonen ◽

J. S. Vetrano ◽

H. L. Heinisch ◽

S. M. Bruemmer

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Austenitic Stainless Steels ◽

Back Diffusion ◽

Metallic Materials ◽

Grain Boundary Characteristics ◽

Radiation Induced ◽

Composition Profiles ◽

Solute Interactions ◽

Boundary Characteristics

AbstractDefect-solute interactions control radiation-induced segregation (RIS) to interfacial sinks, such as grain boundaries, in metallic materials. The best studied system in this regard has been austenitic stainless steels. Measurements of grain boundary composition indicate that RIS of major alloying elements is in reasonable agreement with inverse-Kirkendall predictions. The steep and narrow composition profiles are shown to result from limited back diffusion near the boundary. Subsequently, defect-solute interactions that affect the near-boundary defect concentrations strongly affect RIS. The variability in measured RIS may in part be caused by grain boundary characteristics.

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Study on the Durable Factors of the Grain Size in 18CrNiMo7-6 by Heating and Cooling Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.194-196.228 ◽

2011 ◽

Vol 194-196 ◽

pp. 228-231 ◽

Cited By ~ 5

Author(s):

Jin Xin Liu ◽

Zhi Jun He ◽

Lian Hai Wang ◽

Gui Ping Feng ◽

Zheng Jun Zhang ◽

...

Keyword(s):

Grain Size ◽

Grain Boundaries ◽

Alloying Elements ◽

Abnormal Growth ◽

Furnace Heating ◽

Heating And Cooling ◽

Cooling Method ◽

Long Time ◽

Individual Grains

Study researches durable factors of the grain size in 18CrNiMo7-6 by heating and cooling method. Results show that alloying elements Nb and Al have a strong pining effect on the grain boundaries, Al/N ratio between 2.0-2.5 can promote the grain not to grow up for a long time, and refine grains significantly with furnace heating and after carburizing-quenching once, and can inhibit the abnormal growth of individual grains.

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Metallurgical Effects of Grain Boundary Ledges

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100078225 ◽

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.

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