The effect of grain boundary segregation of boron in cast alloy 718 on HAZ microfissuring -- a SIMS analysis

Journal Article · Fri Aug 01 04:00:00 EDT 1997 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(97)00017-7· OSTI ID:532878

Huang, X; Chaturvedi, M C ^[1]; Richards, N L ^[2]; Jackman, J ^[3]

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1. Univ. of Manitoba, Winnipeg, Manitoba (Canada). Dept. of Mechanical and Industrial Engineering
2. Bristol Aerospace Ltd., Winnipeg, Manitoba (Canada)
3. CANMET, Ottawa, Ontario (Canada)

Secondary ion mass spectroscopy (SIMS) has been used to examine grain boundary segregation in cast alloy 718. The relationship between the boron segregation and the microfissuring tendency in heat affected zones (HAZ) around electron beam welds is discussed in this study. It is concluded that two types of segregation, namely equilibrium and non-equilibrium segregation, occurred during the homogenization heat treatment of the base material. Water quenching after the homogenization treatment inhibited non-equilibrium segregation of boron and other trace elements owing to insufficient time for diffusion of solute-vacancy complexes to occur. Intermediate cooling rates such as air cooling enhanced both non-equilibrium and equilibrium segregation, since equilibrium segregation occurred during holding at the heat treatment temperature. The value of net segregation produced by a combination of equilibrium segregation and non-equilibrium segregation varied with temperature in a U-shape. The nature of the grain boundary in the cast alloy was examined by using an electron backscattered diffraction (EBSD) technique and it was found that 93% of the grain boundaries were of the random type ({Sigma} > 49). The weldability of this alloy was found to be closely related to the grain boundary segregation of boron, i.e., the variation of HAZ total crack length (TCL) with pre-welding heat treatment temperatures has a trend similar to that of boron segregation with temperature after air cooling. Mechanisms for the effect of boron on HAZ microfissuring have been proposed.

• Sponsoring Organization: Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada)
• OSTI ID: 532878
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 8 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BORON
DATA
GRAIN BOUNDARIES
HEAT AFFECTED ZONE
HEAT TREATMENTS
INCONEL 718
MICROSTRUCTURE
SEGREGATION