Abstract
Two isothermal sections of the Ni-Cr-Ta ternary system at 1200 °C and 1300 °C have been determined by using electron probe microanalysis, energy dispersive spectroscopy and differential scanning calorimeter. A Laves phase (Ni, Cr)2Ta(HT)(C14 structure) with large solid solubility stabilized by the Ni addition was determined in both two isothermal sections. The composition range of this phase was about 25.8–66.0 at.% Cr, 2.5-44.3 at.% Ni, and 24.0-40.0 at.% Ta at 1200 °C, which increased with raising temperature. The melting point of the Ni-Cr alloys decreased with the addition of Ta. No ternary compound was found in both these two isothermal sections. The present work could be significant for practical application of nickel-based alloys and future thermodynamics assessment of the Ni-Cr-Ta ternary system.
Highlights
Nickel-based superalloys have been applied in the aerospace field due to their excellent high-temperature properties, oxidation and corrosion resistance in the extreme harsh environment [1,2].with higher industrial requirements in the structure materials for high-temperature applications in aviation field, materials capable of better mechanical strength, oxidation and corrosion resistance are required
The phase relationship of the Ni-Cr-Ta ternary system at 1200 ◦ C was established from 33 alloys annealed for 35 days
The microstructure and XRD results of typical alloys annealed at 1200 ◦ C for 35 days are presented in Figures 2 and 3, respectively
Summary
Nickel-based superalloys have been applied in the aerospace field due to their excellent high-temperature properties, oxidation and corrosion resistance in the extreme harsh environment [1,2]. Several investigators [23,24,25,26,27,28] have assessed the thermodynamic database of this binary system with CALPHAD method and first-principles calculation. In 1987, Venkatraman et al [32] reviewed the Cr-Ta system, in which two terminal solid solutions bcc-(Cr), bcc-(Ta) and intermediate phase Cr2 Ta formed from eutectic reaction occurred at 1760 and 1965 ◦ C, respectively. % Ta. there is no ternary compound except for a Laves phase Cr2 Ta (hexagonal, MgZn2 -type, a = 4.844 Å, c = 7.9091 Å) in the isothermal section at 1100 ◦ C, according to Nikolaev’s et al experimental phase diagram [37].
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