LIQUIDUS SURFACE AND MELTING DIAGRAM OF THE TERNARY Ni–Ti–Zr SYSTEM IN RICH IN NICKEL AREA OF CONTENTS

Abstract

Multicomponent alloys based on Ni–Ti system known as high-temperature corrosion-resistant materials that have an attractive combination of mechanical, chemical and physical properties and are used as structural materials and functional diversification purposes. The ternary alloys of the Ni–Ti–Zr system attract attention, in particular, due to their ability to crystallize in an amorphous state at relatively low cooling rates, that is, they have the ability to form so-called bulk amorphous alloys. Literature data concern phase equilibria in the ternary system are rather limited. The system was studied in temperature interval from 700 °С to the liquidus surface in the concentration range from 0 to 50% (at.) Ni by Eremenko with co-authors (1988-1992). There is the only work in the solid / liquid equilibria region with a nickel content of more than 50 % (at.) – Liu X.J. et al (2015) – isothermal sections at 1000 and 1200 °С, that does not give an idea about crystallization processes. Besides in our previous work the solidus surface projection was constructed. In present work we present the results about the phase equilibria in the melting / crystallization region in the concentration range from 75 to 100 % (at.) Ni. The arc-melting alloys were studied by scanning electron microscopy with electron probe microanalysis (SEM / EPMA) and differential thermal analysis (DTA). Based on the results of the experimental study the liquidus surface projection and the melting diagram of the ternary one Ni–Ti–Zr system in the region Ni–Ni3Ti–Ni7Zr2 are constructed. The liquidus surface consists of four fields of primary crystallization – solid solutions of ⟨Ni⟩, ⟨Ni3Ti⟩, ⟨Ni5Zr⟩ and ⟨Ni7Zr2⟩. The liquidus temperature decreases from the bounding binary systems to the ternary one to a minimum at 1182 °С at the point Ni84.5Ti7.9Zr7.6 of the ternary eutectics composition LЕ1 ↔ ⟨Ni⟩ + ⟨Ni3Ti⟩ + ⟨Ni5Zr⟩. The invariant point coordinates on liquidus surface were established: LU1 + ⟨Ni7Zr2⟩ ↔ ⟨Ni5Zr⟩ + ⟨Ni3Ti2⟩ – Ni83.0Ti8.5Zr8.5, 1190 °С; lе3 ↔ Ni + Ni5Zr – Ni87.4Ti4.5Zr8.1, 1187 °С; lе2 ↔ Ni3Ti + Ni7Zr2 – Ni76.3Ti13.2Zr10.5, 1288 °С.