Effect of the Phase Composition of a Titanium Nickelide-Based Alloy on the Formation of Liquid in Sintering

• Published in: Russian metallurgy Metally Vol. 2020; no. 5; pp. 549 - 557
• Main Author: Senkevich, K. S.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.05.2020; Springer Nature B.V
• Subjects: Alloying elements; Alloys; Argon; Chemical elements; Chemistry and Materials Science; Composition effects; Differential thermal analysis; Eutectic reactions; Heating; Liquid phases; Materials Science; Metallic Materials; Nickel; Nickel base alloys; Nickel compounds; Nickel titanides; Oxidation; Phase composition; Phase transitions; Shape memory alloys; Sintering; Titanium; Titanium compounds; eutectic; Ti; oxide; titanium nickelide-based alloys; liquid-phase sintering; phase transformations; Ni; intermetallic phases; O
• ISSN: 0036-0295; 1555-6255; 1531-8648
• DOI: 10.1134/S0036029520050134

The formation of a liquid phase in titanium nickelide–based alloys, which are enriched in nickel (55.8–55.9 wt %) and abundant in Ti 2 Ni/Ti 4 Ni 2 O x phase intermetallic particles, is studied. The phase transformations in the alloys are investigated during heating in argon and helium atmospheres in a temperature range of 900–1200°C by differential thermal analysis. The cause for the formation of liquid in the alloys in a gas medium is found to be their oxidation. Oxidation results in the redistribution of the main chemical elements of the alloy on its surface and the formation of titanium- and nickel-rich phases. This leads to the eutectic transformation TiNi + TiNi 3 → L . On heating in a vacuum, the formation of liquid is possible only in the alloy characterized by a high volume fraction of Ti 2 Ni/Ti 4 Ni 2 O x phase particles. The precipitation of the particles during melting of the alloy depletes its matrix of titanium; this leads to a substantial increase in the nickel content in the matrix as compared to the total nickel content in the alloy. This effect, likely in combination with oxidation, also initiates the eutectic reaction in heating. Liquid-phase (supersolidus) sintering is shown to be possible for titanium nickelide–based alloys due to the eutectic reaction.