Plastic Deformation Behavior of Ni 3 X(X=Nb, Ti, Sn) Type HCP-Based Intermetallics with the Geometrically Close-Packed S
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Plastic Deformation Behavior of Ni3X(X=Nb, Ti, Sn) Type HCP-Based Intermetallics with the Geometrically Close-Packed Structure Koji Hagihara, Takayoshi Nakano and Yukichi Umakoshi Department of Materials Science and Engineering & Handai Frontier Research Center, Graduate School of Engineering, Osaka University, 2-1 , Yamada-oka, Suita, Osaka 565-0871 , Japan ABSTBACT In this paper, our recent results on the plastic deformation behaviors of Ni3X-type hcp-based GCP compounds, such as D0a-Ni3Nb, D019-Ni3Sn and D024-Ni3Ti, are summarized. The similarity and difference of their plastic behavior are discussed focusing on the correlation with the characteristic features of their crystal structures. The criterion for the occurrence of yield stress anomaly (YSA) by slip on the basal plane is also discussed. INTRODUCTION Some Ni3X-type compounds (X=Al, Nb, Ti, etc.) have been of great interest as a strengthening phase in superalloys. Those Ni3X-type compounds are known to crystallize in so-called geometrically closely-packed (GCP) structures. Figure 1 shows five representatives of the GCP structures such as L12, D024, D019, D0a and D022 and the characteristic features of their crystal structures. They are constructed by several stacking sequences of common close-packed plane with combination of a twofold hexagonal layer (h-layer) and a threefold cubic layer (c-layer). In addition, X atoms on the close-packed plane show some ordered arrangements: triangular-type (T-type), rectangular-type (R-type) and compound-type (TR-type) in the GCP phases [1,2]. Concerning the plastic behavior of the Ni3X-type compounds, much information can be available for the materials with the L12 structure (ex. Ni3Al [3]), while information on compounds with other GCP structures is still limited [4]. Recently, we investigated plastic behaviors of some Ni3X-type compounds with different GCP structures such as Ni3Nb (D0a) [5], Ni3Ti (D024) [6] and Ni3Sn (D019) [7]. The crystal structures of D0a-Ni3Nb, D024-Ni3Ti and D019-Ni3Sn are represented by using the above signs to be hR-, chT- and hT-structure, respectively. All the three structures are based on the hcp unit cell when the Ni and X atoms are not distinguished. Since crystal structures in the GCP compounds are related one another, it was expected that they show a similar plastic behavior by slip on the common close-packed planes. Indeed, a strong yield stress anomaly (YSA) was observed in all
Figure 1
The crystal structures of the various Ni3X-type GCP compounds.
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the three compounds investigated, similarly in Ni3Al [3]. The main purpose in this paper is therefore to summarize our recent results on the plastic deformation behaviors of Ni3X-type hcp-based compounds. The similarity and difference of their plastic behaviors are discussed, and the mechanism for the occurrence of YSA by slip on the basal plane is also described. EXPERIMENTAL PROCEDURE Single crystals of Ni3Nb and Ni3Ti and crystals with directionally oriented grains of Ni3Sn were grown by the floating zone method u
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