An analysis of high-temperature microstructural stability and mechanical performance of the Hastelloy N-Hastelloy N Superalloy joint bonded with pure Ti

Abstract

The Hastelloy N superalloys were transient liquid phase bonded to themselves using pure Ti foil at 1223–1373K for 1h. The microstructure was examined using SEM, TEM and HRTEM analysis, and mechanical performance was evaluated by a shear test. Prolonged thermal exposure at 873–1173K was also performed for the joints, to examine their microstructural sensitivity to elevated temperatures. Efforts were made to reveal the relationship between the temperature-dependent microstructure and mechanical properties. Results indicate that two reaction zones (Zones 1 and 2) occur in the joint, with Zone 1 close to the Hastelloy N. The microstructure of Zone 1, produced through the eutectic melting of Cr9Mo21Ni20 and Ni3Ti intermetallics, is less sensitive to the joining temperature, while the microstructure of Zone 2 is strongly dependent on the joining temperature. The joint strength, as revealed, is closely related with the microstructure of Zone 2. The maximum joint strength obtained is 320.3MPa. The results of thermal exposure show that the joint can maintain microstructural stability below 973K. The microstructural evolution of joint during thermal exposure and its influence on mechanical performance were revealed. The performed work will provide basic data to join the Hastelloy series superalloys.