Effect of temperature and time, the interlayer on microstructure and mechanical properties of Transient Liquid Phase (TLP) bonding of AISI321 stainless steel

According to the industry’s need to an appropriate bonding process for components made of AISI 321 austenitic stainless steel, which is used in power-plant parts such as turbines, transient liquid phase (TLP) bonding of AISI 321 steel using MBF-30 and MBF-20 interlayers was studied in this research. TLP bonding was performed in a vacuum furnace at 1050, 1100 and 1150 oC for 30-120 minutes. The microstructural studies were conducted on the joints using an optical microscope and an scanning electron microscope (SEM). Phase analysis of the joints was also performed a SEM/EDS and XRD system. To investigate the distribution of elements across the joints, line scan analysis was used. The shear strength test and the microhardness measurement test were conducted on the joints, in order to study the joints’ mechanical properties. The minimum time or complete isothermal solidification at 1050, 1100 and 1150oC was obtained as 75, 45 and 30 minutes, respectively. At the incomplete isothermal solidification condition, Fe-B, Cr-B, Ni-Si and Ni-B phases were observed at the joint centerline and diffusion affected zone (DAZ). With increasing bonding temperature and time, more homogenous joint, lower hardness at the different zones of the joints and higher shear strength were obtained. The maximum shear strength for MBF-30 interlayer was obtained as 99 and 98 percent of that of the base metal, and for MBF-20 interlayer was obtained as 95 and 94 percent of that of the base metal, respectively.