Microstructure and mechanical properties of transient liquid phase (TLP)-bonded Ni3Al intermetallic compounds

Abstract

This paper investigates microstructure and mechanical properties of transient-liquid-phase (TLP) bonding for the joining of Ni3Al intermetallic compound. The jointing was carried by using AWS BNi-2 interlayer in a vacuum furnace at 1050 °C. Effects of holding times for 30, 60, 90, and 120 min on the microstructure and mechanical properties of the joint have been investigated. The microstructure of samples was evaluated using optical and scanning electron microscopes (SEM). Phase identification was carried using energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). Mechanical properties of joints were studied by hardness profilometry across the interface as well as shear test. Results show that no isothermally solidified zone has been formed in holding time up to 120 min. Also, solidification cracking was observed in the centerline of joints. EDS analysis showed that the centerline is rich in boron and some boride intermetallic compounds. Increasing holding time is associated with a decrease in the amount of brittle phases in the athermally solidified zone. Microhardness profilometry across the interface show that the maximum hardness is attained in the middle of the joint. This is attributable to the fact that the center of the joint is rich in hard nickel and chromium boride phases. Results also show that both hardness and shear strength of the joint increase with increasing holding time. Fractography results indicate that fracture takes place in a brittle mode.