A study of microstructure and ductility of directionally solidified Ni 50 Al 20 Fe 30
- PDF / 183,450 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 207 Views
MATERIALS RESEARCH
Welcome
Comments
Help
A study of microstructure and ductility of directionally solidified Ni50 Al20 Fe30 J. Chen, J. H. Lee, and Y. T. Lee High Temperature Materials Laboratory, Korea Institute of Machinery & Materials, 66 Sangnam Dong, Changwon, Kyungnam, 641-010, South Korea
Q. Zheng, Y. Yu, Y. A. Li, Y. J. Tang, and Z. Q. Hu Institute of Metal Research, Academia Sinica, 72 Wenhua Road, Shenyang, 110015 People’s Republic of China (Received 7 August 1996; accepted 22 May 1997)
The microstructure and ductility of directionally solidified Ni50 Al20 Fe30 were studied. Calculation and experiment show that the elastic modulus of the sample with completely eutectic lamellar structure is higher than that of the sample with dendritic structure. During deformation, in the samples with dendritic structure, some load is transferred from the proeutectic area to the g-rich eutectic area and enhances the ductility of the sample. The existence of thick interdendritic g phase and thick lamellar g phase in the eutectic area of the dendritic sample is very effective in suppressing the microcrack propagation and also contributes to the ductility enhancement. The ordered nickel aluminide, NiAl, exhibits an attractive combination of properties such as high melting temperature, high stiffness, and low density, thereby offering the potential for use as a high temperature structural material, either as single crystals or the matrix for advanced composites.1 However, the recent application of NiAl as a structural material is seriously restricted because of its low ductility at ambient temperature. Ductile phase reinforcement is a well-established method to improve ductility and toughness of brittle materials.2,3 Macroalloying with 20–40 at. % Fe to introduce ductile g phase (fcc structure) as a reinforcement to the brittle b phase (bcc base-ordered B2 structure) was studied in rapidly solidified material.4,5 When the Al content was fixed at 20 at. %, the maximum ductility (17% tensile plastic strain) was obtained in melt-spun ribbon containing 30 at. % Fe. The ductility of Ni50 Al20 Fe30 was further studied,6,7 and directional solidification method was used to further improve its ductility.8–10 A tensile plastic strain of 10% was obtained by this processing technique. Recently, it was found that the ductility of a directionally solidified Ni50 Al20 Fe30 sample with dendritic structure, which was grown at a higher growth rate, shows higher ductility than that of a sample with completely lamellar structure, which was grown at a lower growth rate.11 This study was undertaken to understand the structural features and the role of ductile phase geometry and distribution in the ductility enhancement. The Ni50 Al20 Fe30 ingots, approximately 70 mm long and 7 mm in diameter, were directionally solidified by J. Mater. Res., Vol. 13, No. 2, Feb 1998
http://journals.cambridge.org
Downloaded: 21 Mar 2015
a modified Bridgman method. The growth rates were 0.2 and 1.0 mmymin, respectively. Three samples were grown at each grow
Data Loading...
