Investigators: R. J. Schaefer, M. D. Vaudin, and D. R. Black

Technical Description:

This project seeks to characterize the defects which occur in single-crystal nickel-based metal castings, identify the processing conditions which lead to their formation, and identify steps which industry could take to reduce their incidence. This work is carried out as one of the activities of the Consortium on Casting of Aerospace Alloys, that links NIST to a group of industries, universities, and government agencies.

Technical Objectives:

• Develop classification system, based on experience of Consortium's industrial members, to identify the specific types of defects which cause single-crystal superalloy castings to be rejected during inspection.

• Characterize the geometry and crystallography of the different types of defects and identify solidification mechanisms which could lead to the production of such features.

• Identify thermal conditions during solidification of the casting which cause defects to form by the action of the proposed solidification mechanisms.

• Identify modifications of casting practice which could reduce the incidence of specific types of defects.

Anticipated Outcome:

• Improved guidelines will be developed for the design of single crystal casting processes to avoid the conditions which lead to defect formation.

• More precise criteria will be developed for classifying defects in single crystal castings and thus for identifying the conditions which are responsible for their formation.

Accomplishments for FY 1995:

• Developed model describing the thermal conditions which lead to the formation of defects known as "zebras" on horizontal surfaces of single crystal castings.

• Used X-ray topography to characterize the development of large-scale misalignment patterns in crystal structure during growth of single crystal components.

• Used electron backscattering patterns (EBSP) to measure the small-scale misalignments in single crystal components.

Impacts and Technical Highlights:

• Criteria for prevention of undesirable "zebra" defects were established and made available to manufacturers for their use in design and production of castings.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister