Anisotropy of grain boundary segregation in Σ = 5 bicrystals of α-iron

Lejček, Pavel; Adámek, J.; Hofmann, S.

doi:10.1016/0039-6028(92)90201-g

Cited by 46 publications

(28 citation statements)

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“…Recently the segregation of Si, P, and C was simultaneously measured at various well-characterized grain boundaries in bicrystals of an a-Fe base multicomponent alloy by Auger electron spectroscopy [11][12][13]. From the temperature dependences of the boundary composition, the segregation enthalpies and entropies were determined according to equation (13) assuming wl = wM and saturation coverage to be unity, and considering site competition effects.…”

Section: Grain Boundary Segregation Diagramsmentioning

confidence: 99%

“…Given the relation between the activity and molar concentration Xi, ai = "yiXi (12) where "r~ is the activity coefficient of component i, the segregation equation is then [8] …”

Section: General Relationshipsmentioning

confidence: 99%

“…In these diagrams, the segregation enthalpies AH] of the solutes I for pure binary systems were used to describe the dependence of the segregation on solid solubility in a-iron and on boundary orientation. The experiments suggest the possibility of expressing this dependence as a sum of two independent terms [11][12][13].…”

Section: Introductionmentioning

confidence: 98%

“…Therefore AH] is an independent, fundamental characteristic of the segregation of solute I in matrix M. From this point of view the tendency of a solute to segregate at grain boundaries is better characterized by more fundamental thermodynamic quantities such as the segregation enthalpy as compared to the enrichment ratio [10]. Recently, the first experimentally determined segregation diagrams were constructed from measured solute segregation at well-characterized grain boundaries in [100] tilt bicrystals of an Fe-3.5 at % Si alloy containing traces of phosphorus and carbon [11][12][13]. In these diagrams, the segregation enthalpies AH] of the solutes I for pure binary systems were used to describe the dependence of the segregation on solid solubility in a-iron and on boundary orientation.…”

Section: Introductionmentioning

confidence: 99%

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Grain boundary segregation diagrams of α-iron

Lejček

Hofmann

1993

Interface Sci

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Based on thermodynamic analysis of interracial segregation, the segregation enthalpy AH ~ of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface 9 and the solid solubility limit X~ at temperature T and can be written as AH~ X;) = AH*(~) + vR[Tln(X;)]In this equation, the structural dependence of interfacial segregation is contained in AH*(~) which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [T ln(X~)] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [T In(X~)]mas. The parameter v > 0 represents the relationship between the activity a} of a solute at the bulk solid solubility limit in a given matrix and X~, a} -(X~) ", and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of a-iron, the averaged value = 0.77 was determined. Values of AH*(4~) range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of oL-iron.

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Section: Grain Boundary Segregation Diagramsmentioning

confidence: 99%

“…Given the relation between the activity and molar concentration Xi, ai = "yiXi (12) where "r~ is the activity coefficient of component i, the segregation equation is then [8] …”

Section: General Relationshipsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Grain boundary segregation diagrams of α-iron

Lejček

Hofmann

1993

Interface Sci

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“…In the former case, the grain boundary concentration of solutes are essentially governed by their segregation enthalpies, which depend on the boundary orientation as a function of the deviation angle of boundary planes. 25,26) The influence of the change in the segregation enthalpies on grain boundary segregation is considered to be common for each solute and irrelevant to interactions between solutes, then the present result on the grain boundary periodic alternating segregation based on the divorced coincident segregation is not influenced so much by prior austenitic grain boundary structure.…”

Section: Other Issuesmentioning

confidence: 90%

Nano-investigation on Grain Boundary Periodic Alternating Segregation Based on Divorced Coincident Segregation Mechanism, Resulted in the Replacement of Conventional Site Competition in Steels.

Mabuchi

Koseki

2000

ISIJ International

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The segregation mechanism of alloying elements in prior austenitic grain boundaries of embrittled 5 % Ni steels has been investigated by AES in previous studies, while that of improved 5 % Ni steels has not been clarified yet. In the present study, the segregating behavior of alloying elements in improved 5 % Ni steels has been elucidated for the first time by applying FE-TEM with respect to the effects of soluble Al on the suppression of temper embrittlement and hydrogen embrittlement in the steels.It is consequently made clear by applying FE-TEM-EDS that alloying elements tend to segregate coincidently to grain boundaries, showing the asymmetric segregation according to solute interactions. The observed behavior is newly defined as the divorced coincident segregation, which is considered to result from the moderate site competitions in the deep potential well of McLean's equilibrium segregation. The divorced coincident segregation was investigated further along grain boundaries, where the periodic segregation of Al and Si was found to vary alternately along grain boundaries analyzed.The beneficial effect of soluble Al on the two types embrittlement is attributed to the mechanism of spot toughening through the periodic decrease of solutes in grain boundaries. The principle of the divorced coincident segregation proposed in 5 % Ni steels can be applicable not only to ordinary steels but also to other poly-crystalline alloys in improving their properties.KEY WORDS: segregation mechanism; cosegregation; site competition; divorced coincident segregation; asymmetric segregation; periodic alternating segregation; alloying element; aluminum; solute interaction; repulsive interaction; temper embrittlement; hydrogen embrittlement; spot toughening; 5 % nickel steel; plaincarbon steel; HY130 steel; AES; FE-TEM; FE-TEM-EDS. elements in grain boundaries was investigated for the first time by adopting Field-Emission Transmission Electron Microscopy (FE-TEM) 13,14) equipped with Energy Dispersive X-Ray Spectroscopy (EDS) to the improved 5% Ni steels without intergranular fractures. 9,10) "Divorced coincident segregation" with asymmetric profiles of segregated solutes has been newly defined for the segregation mechanism of alloying elements according to the moderate site competition in the deep potential well of McLean's equilibrium segregation. 15) The divorced coincident segregation in the improved 5 % Ni steels was further investigated by employing FE-TEM-EDS to find the periodic alternating segregation along grain boundaries. 16) The three-dimensional contour map of segregated solutes was eventually proposed from adopting the point symmetric concept of the periodic alternating segregation based on the divorced coincident segregation mechanism.Then, the present paper describes the formation mechanism of the periodic alternating segregation based on the divorced coincident segregation mechanism in the 5 % Ni steels and a plain-carbon steel, clearly demonstrating the repulsive interaction between Al and Si in grain boundaries...

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Role of entropy in anistropy of grain boundary segregation

Lejček

1998

Surf. Interface Anal.

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From the viewpoint of existence of linear dependence between entropy and enthalpy of grain boundary segregation, the meaning of the entropy term is discussed. It is suggested that negative values of segregation entropy for silicon segregation at individual grain boundaries in α‐iron reflect an ‘ordering’ tendency of the interfaces due to the presence of silicon. On the other hand, positive values of segregation entropy suggest a ‘disordering’ of the structure of these grain boundaries by segregation of carbon and mainly of phosphorus. The effect of ‘disordering’ is especially high for special grain boundaries with compact intrinsic structure, resulting in high values of segregation entropy. The slope of the dependence of enthalpy on entropy of solute segregation at different grain boundaries can be considered as a compensation temperature. Its existence implies that an anisotropy of grain boundary chemical composition will possess a qualitatively different character above and under this temperature. This anisotropy measured above the compensation temperature will be characterized by high values of grain boundary concentration for special boundaries as compared to general boundaries. © 1998 John Wiley & Sons, Ltd.

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Anisotropy of grain boundary segregation in Σ = 5 bicrystals of α-iron

Cited by 46 publications

References 12 publications

Grain boundary segregation diagrams of α-iron

Grain boundary segregation diagrams of α-iron

Nano-investigation on Grain Boundary Periodic Alternating Segregation Based on Divorced Coincident Segregation Mechanism, Resulted in the Replacement of Conventional Site Competition in Steels.

Role of entropy in anistropy of grain boundary segregation

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