Synthesis of Ni-Cr-B-Si-Fe-based interlayer alloy for transient liquid phase bonding of Inconel 718 superalloy by mechanical alloying process

Abstract

A Ni-Cr-B-Si-Fe-based filler alloy powder has been synthesized by mechanical alloying technique in a high-energy ball mill to join Inconel 718 (IN 718) by transient liquid phase (TLP) bonding. The structural analysis of the synthesized alloy powders was done by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), field emission transmission electron microscope (FETEM), and laser particle size analyzer (LPSA). Thermal characterization was done by differential scanning calorimetry (DSC). The particle size of 60-h milled powders was found to be 15.4 μm and exhibits equiaxed shapes. Analysis of results reveals that during the milling process, elemental powder mixture gradually transforms to a nano-crystalline non-equilibrium face-centered cubic structured (FCC) Ni (Cr, Fe, Si, B) solid solution alloy. For the powder after 60-h milling, the crystallite size measured by XRD was found to be 4.0 nm. The lattice constant of nickel in the milled powder mixture decreased up to 5 h of milling and increased with a further increase in milling time. Dissolution of Si, B, Cr, and Fe into the Ni matrix resulted in the change of lattice constant of the alloy powder. The DSC result of 60-h milled powders reveals an endothermic peak at 1023.5 °C, which is attributed to the melting of the alloy powder. The activation energy of the milled powder reduced with milling time; as a result, the diffusivity of the elements in the filler metal increased. The activation energy of the 60-h milled alloyed powders was found to be 2714.67 KJ/mol. IN 718 superalloy was joined by the TLP bonding process. The microstructure of the TLP-bonded IN 718 joints showed three distinct zones in the bond area. Increasing the bonding temperature from 1050 to 1100 °C resulted in a 21% increase in the shear strength of TLP-bonded IN 718 alloy.