Superplasticity in NiAl and NiAl-based alloys
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X.H. Du Institute of Metal Research, The Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China, and School of Material Sciences and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
L.Z. Zhou Institute of Metal Research, The Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
B.D. Zhou School of Material Sciences and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
Y.H. Qi and G.S. Li Institute of Metal Research, The Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China (Received 16 December 2001; accepted 13 June 2002)
Superplastic deformation was realized on NiAl and NiAl-based alloys prepared by both common casting and directional solidification. Directionally solidified NiAl–27Fe–3Nb alloy as well as conventionally cast NiAl, NiAl–25Cr, NiAl–9Mo, NiAl–20Fe–Y.Ce, and NiAl–30Fe–Y alloys exhibited typical deformation characteristics shown in conventionally superplastic materials. NiAl and NiAl-based alloys could be divided into three categories depending on their different superplastic behavior: finely grained structure (NiAl–9Mo, NiAl–25Cr, NiAl–20.4Fe–Y.Ce, NiAl–30Fe–Y), coarsely grained structure (NiAl), and columnar structure (NiAl–27Fe–3Nb). The corresponding deformation mechanisms for fine-grained structure, coarsely grained structure, and columnar structure were grain boundary sliding or grain boundary sliding accompanied by dynamic recrystallization, dynamic recovery and recrystallization, and intragrain dislocation slip, respectively.
I. INTRODUCTION
Intermetallics based on nickel aluminides have attracted widespread attention for potential use in hightemperature applications because of their outstanding properties including high melting points, low densities, and excellent capacity of heat transmission. In past decades, significant improvement in elevated temperature strength, processing, and design methodology for NiAl alloys has been achieved.1 However, their applications have been limited due to poor forming ability from the lack of toughness and low ductility at room temperature. It is well known that superplastic forming (SP) is a viable method to dissolve the hard-to-machine problem. a)
Address all correspondence to this author. J.T. Guo, Institute of Metal Research, The Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China. e-mail: [email protected]
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J. Mater. Res., Vol. 17, No. 9, Sep 2002
Superplasticity has been observed often in various intermetallics and has achieved significant progress in the fundamental understanding of deformation mechanism. Similar to that of conventional metals, the commonly acceptable deformation mechanism of intermetallics is grain boundary sliding (GBS), and the used technique for producing superplastic intermetallics is to develop a multiphase, fine-grained, equiaxed microstructure.2 Nevertheless, coarsely grained structure superplasticity has been observed in iron aluminides.3–5 This pheno
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