Improved Strength and Ductility of Ni 3 Al by Boron Modification and Rapid Solidification
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This research was supported in part under Air Force Contract F33615-81-C-5059.
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Improved Strength and Ductility of Ni3AI by Boron Modification and Rapid Solidification A. I. TAUB, S. C. HUANG, and K. M. CHANG The intermetallic compound Ni3A1 is unusual in that the flow stress increases with temperature, reaching a peak value at approximately 800 ~ This behavior would make the compound attractive as a refractory material were it not for the low ductility exhibited by the cast material at ambient temperature. This low ductility of polycrystalline Ni3A1 has been attributed to the inherent weakness of the grain boundaries, since single crystals of the compound have been shown to exhibit high ductilities in all crystal orientations, even at room temperature. 4 In an attempt to improve the ductility of the polycrystalline form of the compound, Aoki and Izumi 5'6 introduced small additions of boron to the binary intermetallic. The boron addition resuited in a considerable improvement in the ductility, more than 30 pct plastic strain for addition of approximately 0.5 at. pct boron compared to zero ductility for unmodified Ni3A1 processed under identical conditions. This is consistent with a recent calculation of the effect of boron on the binding strength of a Ni cluster, in which Messmer and Briant7 showed that the boron acts to enhance the electronic bonding between the Ni atoms. An improvement of the ductility of sulfur doped nickel by boron additions has also been attributed to grain boundary modification. 8 In this paper, we will report the preliminary results of an investigation into the effect of cooling rate on the meA.I. TAUB, S.C. HUANG, and K.M. CHANG are all Staff Metallurgists with General Electric Corporate Research and Development, P. O. Box 8, Schenectady, NY 12301. Manuscript submitted August 10, 1983. METALLURGICALTRANSACTIONS A
chanical properties of the Ni3AI intermetallic phase. In particular, the effects of rapid solidification on the strength and ductility of boron modified Ni3A1 will be discussed. The ingots of Ni3A1 with various boron additions were prepared by vacuum induction melting using high purity Ni, A1, and NiB. The ingots were then processed into ribbon form (approximately 6 mm wide by 20 to 35/xm thick) via melt spinning in vacuum. Details of the melt spinning process for Ni based alloys have been presented elsewhere. 9 The mechanical properties of the ribbons
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