Experimental Investigations of Ni-Ti-Ru System: Liquidus Surface Projection and 1150 °C Isothermal Section

• Published in: Materials 2023-07, Vol.16 (15), p.5299
• Main Authors: Ma, Dupei, Li, Zhi, Liu, Yan, Zhao, Manxiu, Hu, Jingxian
• Format: Article
• Language: English
• Subjects: Alloys; Analysis; Annealing; Binary system; Calorimetry; Casting alloys; Cooling rate; Couples; Diffraction; Diffusion barriers; Electric arc melting; Equilibrium; Heat resistant alloys; Liquidus; Mechanical properties; Metallurgy; Nickel base alloys; Oxidation; Phase stability; Research methodology; Ruthenium; Shape memory alloys; Solid solutions; Solidification; Superalloys; Temperature; Ternary systems; Thermal properties; Thermodynamic models; Thermodynamics; Tubes; X-rays
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16155299

Ruthenium addition inhibits the formation of the topologically close-packed phases in Ni-based superalloys and improves the solid solution strength of Ni-Ti shape memory alloys. Therefore, the Ni-Ti-Ru phase stability is a very valuable indicator of the effects of Ru in Ni-based superalloys and Ni-Ti shape memory alloys. In this study, the isothermal section at 1150 °C and liquidus surface projection of the Ni-Ti-Ru ternary system were determined experimentally using the equilibrated alloy method and diffusion couple method, respectively. Alloys were prepared through the arc-melting of Ni, Ti, and Ru (all 99.99% purity), and then vacuum encapsulation in quartz tubes, followed by annealing at 1150 °C for 36 to 1080 h depending on the alloy composition. Diffusion couples were fabricated by joining one single-phase block (τ1) with one two-phase block (Ni Ti + γ(Ni)), and the couples were annealed under vacuum at 1150 °C for 168 h. Reaction temperatures of as-cast alloys were determined by differential scanning calorimetry performed with heating and cooling rates of 10 °C/min. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure. Seven three-phase regions were found at the 1150 °C isothermal section. Seven primary solidification regions and five ternary invariant reactions were deduced in the liquidus surface projection. A new ternary compound τ1 was discovered in both the isothermal section at 1150 °C and liquidus surface projection. The results aid in thermodynamic modeling of the system and provide guidance for designing Ni-based superalloys and Ni-Ti shape memory alloys.