Effect of Ta addition on microstructure and mechanical properties of dual two-phase Ni 3 Al-Ni 3 V intermetallic alloy
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MRS© Advances © 2019Research MaterialsSociety Research Society RS Advances 2019 Materials DOI: 10.1557/adv.2019.140 OI: 10.1557/adv.2019.38
Effect of Ta addition on microstructure and mechanical properties of dual two-phase Ni3Al-Ni3V intermetallic alloy Kazushige Ioroi*, Yasuyuki Kaneno and Takayuki Takasugi Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
*[email protected]
ABSTRACT Mechanism for the hardening of two-phase Ni3Al-Ni3V intermetallic alloy to which 2 at.% Ta was added in different substitution manners for Ni, Al and V was presented, based on the microstructural observation, alloying behavior and lattice properties of the additive in the constituent phases. The hardening behavior was explained in terms of solid solution hardening in which the mixture rule in the volume fraction of the two constituent phases and the atomic size misfit evaluated from the changes of the lattice parameters were incorporated. Consequently, the hardening for the alloys in which the additives were substituted for Ni and V was attributed to solid solution hardening. On the other hand, the hardening for the alloy in which the additive was substituted for Al was attributed to the hardening due to microstructural refining in addition to the solid solution hardening.
INTRODUCTION Following a unique microstructural feature of Ni base J-J' type superalloys, so-called Ni base dual two-phase intermetallic alloys have been developed, based on the Ni3Al (L12) and Ni3V (D022) pseudo-binary alloy system shown in figure 1 [1,2]. At the hyper-eutectoid compositions, the microstructures at high temperatures are comprised of primary Ni3Al phase (J') precipitated from Ni solid solution (J) matrix. At low temperatures, the Ni solid solution existing in the channel region is transformed into a eutectoid microstructure consisting of the Ni3Al and Ni3V phases [3-5,6]. The microstructural stability is believed to be high at elevated temperatures because of crystallographically coherent microstructure between the two constituent
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Figure 1. Phase diagram of the Ni3VNi3Al pseudo-binary alloy system constructed from our previous studies [1,2].
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phases, making the dual two-phase intermetallic alloys attractive as advanced hightemperature structural materials. In this study, tantalum (Ta) that stabilizes the two constituent phases [3] and is expected to behave as solid solution strengthener was added in different substitution manners for the constituent elements, Ni, Al and V of the dual two-phase intermetallic alloy. The atomic radius of Ta (0.147 nm) is larger than those of three constituent elements, Ni (0.125 nm), Al (0.143 nm) and V (0.137 nm) if defined by the Goldschmidt radius. First, microstructure, alloying (i.e. part
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