Effect of homogenization duration on microstructure and mechanical properties of TLP-bonded IN 718 joints

This study systematically investigates the influence of homogenization stage duration on both the microstructure and mechanical properties of Transient Liquid Phase (TLP) bonded Inconel 718 (IN 718) joints. The primary objectives were to eliminate detrimental eutectic phases within the Athermally Solidified Zone (ASZ) and avoid adverse effects associated with high-temperature post-bond homogenization. A low-temperature homogenization was implemented for this purpose. To investigate the impact of homogenization duration on the bond quality, comprehensive analyses, including FESEM, and FETEM analysis were carried out. The result showed, homogenization effectively dissolved the precipitates present in the ASZ. Moreover, an increase in homogenization duration results in a more uniform microstructure in the bond, along with an increased volume fraction of γ′ + γ″ phases. Interestingly, the response of homogenization on various zones of TLP Bonding (TLPB); that is, Base Metal Zone (BMZ), Isothermal Solidified Zone (ISZ) and Diffusion Affected Zone (DAZ) was different. Specifically, homogenization dissolves Nb-type boride present in the DAZ and forms γ″ precipitates, resulting in a reduction of boride volume fraction with increasing homogenization duration. After 32 h of homogenization, UTS of the TLP bond was remarkable improved by 220%. Higher homogenization duration also enhanced the ductility of the TLP bonded joint. This study provides valuable insights into optimizing TLPB processes for improved microstructural uniformity and mechanical performance in IN 718 joints.