Improvement of Elevated Temperature Material Properties in Intermetallic Compound Ni 3 Al
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IMPROVEMENT OF ELEVATED TEMPERATURE MATERIAL PROPERTIES IN INTERMETALLIC COMPOUND Ni3AI AKITSUGU FUJITA, TATSUKI MATSUMOTO, MAKOTO NAKAMURA AND YORIMASA TAKEDA Nagasaki Research & Development Center, Mitsubishi Heavy Industries, Ltd., 1-1 Akunoura-machi, Nagasaki 850-91, Japan ABSTRACT Intermetallic compound Ni3Al(y') is one of the major constituents in Ni-base superalloys. But it is not used by itself for structural use because of its low ductility and low strength. In the present study, the improvement of elevated temperature mechanical properties of Ni3Al intermetallic compound is pursued by addition of such elements as Fe, Ti, Cr, V, Nb, Ta, Mo, W, Zr and Hf. These results show that Ni 3AI which contains some elements substituting for Al has better mechanical properties and creep rupture properties than commercial Inconel 713C. INTRODUCTION Intermetallic compound based on Ni 3AI(y') is fully utilized to provide excellent creep properties in Ni-base superalloys. Commercial Ni-base superalloys such as Mar-M247 contain 50 41 60 vol.% y' as precipitates. However, the properties of Ni3Al single phase are not good enough for structural use because of its low ductility and low strength, especially at elevated temperature. Recent studies [1,2] show that B-doped Ni3Al intermetallic compound has quite excellent ductility at room temperature, which is not necessarily so at elevated temperatures. And its creep rupture strength is not high enough compared to commercial Ni-base superalloys. Our present effort is to improve the mechanical and creep rupture properties of intermetallic compound Ni3AI by addition of transition metal elements. EXPERIMENTAL PROCEDURE The alloys used in the present work were prepared by three different procedures; (i) Arc-melting in an argon atmosphere. Most of the tests were carried out with these arc-melted materials. Test piece size (mm): lOxlOxlO0 (approximately) (2) Directional solidification by zone melting. Materials which exhibited good properties in the arc-melting condition were tested in this condition. Test piece size (mm): 9.50 x 400 (approximately) (3) Arc-melting and Hot Isostatic Press (HIP) processed. Some materials having low ductility were tested in this condition. These materials were homogenized at 1050 n 11000 C for 50 hrs in an argon atmosphere. Tensile tests were carried out at room temperature to 1000*C in air with 5 mmo tensile specimen (gauge length 18 mm, for arc-melted materials) and 4 mm$ tensile specimen (gauge length 14 mm, for directional solidified materials). Creep rupture tests were carried out at 760*C and 1000 0 C in air with smooth (4 mm6, GL 25 mm) and notched (4 mmo, wz=1.52) specimens.
Mat. Res. Soc. Symp. Proc. Vol. 133. 01989Materials Research Society
574
RESULTS Improvement of ductility at elevated temperature
Table 1 shows tensile properties of B-doped NiaAl (24 at.%Al) at room have quite excellent ductility at temperature and 600 0 C. The B-doped alloys room temperature [1,2], but not at 600 0 C. Table 2 shows tensile properties of Ni 3Al (24 at.%
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