The role of TLP process variables in improvement of microstructure and mechanical properties in TLP joints of GTD-111/Ni-Cr-Fe-B-Si/GTD-111 system

In this research microstructure and mechanical properties of the transient liquid phase (TLP) joint of GTD-111 superalloy using Ni-7.6Cr-3.4Fe-3.6Si-3B amorphous interlayer were investigated. The effect of joining parameters such as temperature, time and interlayer thickness on the microstructure and mechanical properties of the joint was studied. The results showed that eutectic and intermetallic compounds e.g. nickel-rich and chromium-rich borides, Ni-Si-B compound and eutectic-gamma form continuously in the joint region during cooling. The thickness and continuity of the intermetallic phases decreased with increasing joining time. Moreover, increasing joining temperature to 1180 degrees C led to the elimination of intermetallic phases. The phases were reappeared as the joining temperature was further increased up to 1200 degrees C. In addition, increasing the interlayer thickness led to a thicker eutectic structure in the joint region. Shear strength of the joints increased with increasing holding time. Increasing the bonding temperature led to an increase in shear strength (except 1200 degrees C) which was in agreement with hardness variation. Furthermore, it was shown that homogenization of the samples after the joining process led to a more uniform hardness profile in the joint and significant increase in the shear strength up to 97% of the base metal strength. According to the obtained results the optimum time, temperature, and interlayer thickness for the TLP bonding of GTD-111 are 105 min, 1120 degrees C and 25 mu m, respectively.