The Ni-Ru-Ti (Nickel-Ruthenium-Titanium) System
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hase Diagram Evaluations: Section II
The Ni-Ru-Ti (Nickel-Ruthenium-Titanium) System K.P. Gupta, The Indian Institute of Metals
The Ni-Ru-Ti system has been studied only to a limited extent. Only one pseudobinary section, between the two equiatomic phases NiRu and NiTi, has been established.
Binary Systems The Ni-Ru system [1991Nas] (Fig. 1) seems to be a simple peritectic system, with the peritectic reaction L + (Ru) ↔ (Ni) occurring at 1550 °C. The (Ru) and (Ni) solid solution phase regions are quite wide at the peritectic reaction temperature, ∼50 at.% Ni in Ru and ∼34.5 at.% Ru in Ni, but the solubilities of Ru in Ni and of Ni in Ru decrease reasonably rapidly with decreases in temperature. The Ni-Ti system [1991Nas] (Fig. 2) has three intermediate phases, Ni3Ti, NiTi, and NiTi2, of which the Ni3Ti and NiTi phases melt congruently at 1380 °C and 1310 °C, respectively. The NiTi2 phase forms through a peritectic reaction, L + NiTi ↔ NiTi2, at 984 °C. The Ni3Ti phase is a stoichiometric single-composition phase, and the NiTi2 phase has limited solid solubility (∼1 at.%). The NiTi phase possibly goes through a eutectoid decomposition, NiTi ↔ Ni3Ti + NiTi2, at ∼600 °C. A martensitic transformation occurs in the NiTi phase and has martensite start (MS) at ∼60 °C. Three eutectic reactions, L ↔ (Ni) + Ni3Ti, L ↔ Ni3Ti + NiTi, L ↔ NiTi2 + Ti, and one eutectoid reaction,
Ti ↔ NiTi2 + ␣Ti, occur at 1304, 1118, 942, and 765 °C, respectively. The Ru-Ti system [Massalski2] has only one intermediate-phase RuTi, which melts congruently at ∼2130 °C. Two eutectic reactions, L ↔ (Ru) + RuTi and L ↔ Ti + RuTi, occur at ∼1825 and 1575 °C, respectively. In the wide Tiphase field (up to ∼25 at.% Ru), a solidus-liquidus minimum of ∼1550 °C occurs at ∼15 at.% Ru. The Ti ↔ ␣Ti transformation occurs at and below 882 °C.
Binary and Ternary Phases There are only four binary intermediate phases in the three binaries Ni-Ru, Ni-Ti, and Ru-Ti. No ternary intermediate phase is known to form in the Ni-Ru-Ti system. The structure data for the binary phases are given in Table 1.
Ternary System NiTi and RuTi are both isostructural phases with a CsCltype structure having very similar lattice parameters. Hence, one should expect a complete solid solubility of the two phases in each other. An isopleth for the NiTi-RuTi system was, however, reported by [1980Bor] (as was mentioned by
Fig. 1 Ni-Ru phase diagram [1991Nas]
Journal of Phase Equilibria and Diffusion Vol. 25 No. 5 2004
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Section II: Phase Diagram Evaluations
Fig. 2 Ni-Ti phase diagram [1991Nas]
Fig. 3 Ru-Ti phase diagram [Massalski2]
[1984Ere] in their comparative study of various Ti-Ni-M systems, where M ⳱ group IV to group VIII transition metals) to be of a peritectic type (Fig. 4a), with the peritectic reaction L + RuTi ↔ NiTi occurs at 1570 °C. Since some
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of the known Ni-Ti-M systems with M ⳱ Fe, Co, and Pd show complete solid solubility between the NiTi and MTi phases, [1984Ere] doubted the results of [1980Bor] because the alloys were annealed at 1200 °C for too
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