Accession Number:

ADA199365

Title:

Fracture Mechanisms in Iron and Nickel Aluminides

Descriptive Note:

Final rept. 1 Mar 1984-31 May 1988

Corporate Author:

RENSSELAER POLYTECHNIC INST TROY NY DEPT OF MATERIALS ENGINEERING

Personal Author(s):

Report Date:

1988-08-15

Pagination or Media Count:

47.0

Abstract:

The high cycle fatigue HCF resistance of several boron-doped Nickel Aluminide alloys has been determined over a range of test temperatures. Fatigue and tensile properties of two Ni-rich ternary alloys were much superior to those of the cast 26A1 alloy or a PM alloy with 9.3 Manganese. Crack paths were transgranular in the Ni-rich alloys and intergranular or interdendritic in Ni- 26A1. HCF lives decreased sharply at temperatures above 500C. Crack growth rates increased with temperatures to 600C, in spite of a rising yield stress over the same temperature range, perhaps due to oxygen-induced embrittlement. Single crystals of Ni3A1B displayed a marked flow stress assymetry in tension and compression. Point defects were observed in large numbers these condense into voids, thereby contributing to each crack initiation. The high cycle fatigue HCF and crack growth resistance of several Iron Aluminide-type alloys was determined in the temperature range 25-600C. Long range order DO3 type was effective in prolonging high cycle fatigue lives in Fe-28.1A1, but not in FE- 23.7A1 at 25C. Crack growth rates were higher in the DO3 condition. Fatigue results on both Ni3A1 and Fe3A1 alloys are discussed on the basis of microstructure, surface slip band development and internal dislocation substructures revealed by transmission electron microscopy.

Subject Categories:

  • Properties of Metals and Alloys

Distribution Statement:

APPROVED FOR PUBLIC RELEASE