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Title: The effect of thermal history on intergranular boron segregation and fracture morphology of substoichiometric Ni/sub 3/Al

Abstract

While it has attractive mechanical properties and good corrosion resistance, the usefulness of polycrystalline Ni/sub 3/Al has been restricted because of its propensity for brittle intergranular fracture. While this intergranular brittleness can be aggravated by the intergranular segregation of certain impurities, particularly sulfur, the grain boundaries of Ni/sub 3/Al are intrinsically brittle and Ni/sub 3/Al will fail intergranularly in the absence of detectable impurity segregation. Addition of boron resulted in the fracture morphology changing from primarily intergranular to largely transgranular; and more importantly, the intergranular segregation of boron was conclusively demonstrated. The range of boron concentrations over which these beneficial effects are observed is well within the solubility limit, which has been estimated to be 1.5 at. % (4,5). Rice (6) developed a relationship between equilibrium intergranular segregation and grain boundary cohesion. According to this theory, the potential for intergranular embrittlement by a solute is related to the relative intensity of segregation of the solute to free surfaces as compared to segregation to grain boundaries. Rices theory allowed for the case of a solute segregating more strongly to grain boundaries than to free surfaces. If this difference is sufficiently large (approximately a factor of two), Rice's theory predicts an enhancementmore » of grain boudary cohesion. White and coworkers (4,7) noted the rather unusual phenomenon of boron segregating much more strongly to grain boundaries of Ni/sub 3/Al than to free surfaces, while sulfur (an embrittling impurity) was shown to exhibit the opposite effect.« less

Authors:
; ;
Publication Date:
Research Org.:
Materials Science and Engineering, Univ. of Tennessee, Knoxville, TN 37996-2200
OSTI Identifier:
5246560
Resource Type:
Journal Article
Journal Name:
Scr. Metall.; (United States)
Additional Journal Information:
Journal Volume: 20:7
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM ALLOYS; FRACTURE PROPERTIES; BORON ADDITIONS; METALLURGICAL EFFECTS; NICKEL BASE ALLOYS; BRITTLENESS; CORROSION RESISTANCE; GRAIN BOUNDARIES; IMPURITIES; INTERMETALLIC COMPOUNDS; POLYCRYSTALS; SEGREGATION; SULFUR; ALLOYS; BORON ALLOYS; CRYSTAL STRUCTURE; CRYSTALS; ELEMENTS; MECHANICAL PROPERTIES; MICROSTRUCTURE; NICKEL ALLOYS; NONMETALS; 360103* - Metals & Alloys- Mechanical Properties

Citation Formats

Choudhury, A, White, C L, and Brooks, C R. The effect of thermal history on intergranular boron segregation and fracture morphology of substoichiometric Ni/sub 3/Al. United States: N. p., 1986. Web. doi:10.1016/0036-9748(86)90437-0.
Choudhury, A, White, C L, & Brooks, C R. The effect of thermal history on intergranular boron segregation and fracture morphology of substoichiometric Ni/sub 3/Al. United States. https://doi.org/10.1016/0036-9748(86)90437-0
Choudhury, A, White, C L, and Brooks, C R. Tue . "The effect of thermal history on intergranular boron segregation and fracture morphology of substoichiometric Ni/sub 3/Al". United States. https://doi.org/10.1016/0036-9748(86)90437-0.
@article{osti_5246560,
title = {The effect of thermal history on intergranular boron segregation and fracture morphology of substoichiometric Ni/sub 3/Al},
author = {Choudhury, A and White, C L and Brooks, C R},
abstractNote = {While it has attractive mechanical properties and good corrosion resistance, the usefulness of polycrystalline Ni/sub 3/Al has been restricted because of its propensity for brittle intergranular fracture. While this intergranular brittleness can be aggravated by the intergranular segregation of certain impurities, particularly sulfur, the grain boundaries of Ni/sub 3/Al are intrinsically brittle and Ni/sub 3/Al will fail intergranularly in the absence of detectable impurity segregation. Addition of boron resulted in the fracture morphology changing from primarily intergranular to largely transgranular; and more importantly, the intergranular segregation of boron was conclusively demonstrated. The range of boron concentrations over which these beneficial effects are observed is well within the solubility limit, which has been estimated to be 1.5 at. % (4,5). Rice (6) developed a relationship between equilibrium intergranular segregation and grain boundary cohesion. According to this theory, the potential for intergranular embrittlement by a solute is related to the relative intensity of segregation of the solute to free surfaces as compared to segregation to grain boundaries. Rices theory allowed for the case of a solute segregating more strongly to grain boundaries than to free surfaces. If this difference is sufficiently large (approximately a factor of two), Rice's theory predicts an enhancement of grain boudary cohesion. White and coworkers (4,7) noted the rather unusual phenomenon of boron segregating much more strongly to grain boundaries of Ni/sub 3/Al than to free surfaces, while sulfur (an embrittling impurity) was shown to exhibit the opposite effect.},
doi = {10.1016/0036-9748(86)90437-0},
url = {https://www.osti.gov/biblio/5246560}, journal = {Scr. Metall.; (United States)},
number = ,
volume = 20:7,
place = {United States},
year = {1986},
month = {7}
}