Effect of pressure, temperature and homogenization on the dissolution behavior and mechanical properties of IN718/AISI 304 during transient liquid phase bonding

This research focuses on the effect of bonding pressure, bonding temperature and post-bonding homogenization on the dissolution behavior and mechanical properties of transient liquid phase (TLP) bonding of Inconel 718 and AISI 304 L stainless steel. The findings revealed that higher applied pressure resulted in substantial widening of bond line, due to greater inter-diffusion between insert and base materials. Intermetallic phases in bonded sample under 5 MPa mostly comprised of Nb and Mo borides, while 1-MPa bond consisted of Ni-, Cr-, Ni-Si borides and Ni-Si precipitates. Results of shear strength evaluation implied that higher applied pressure improved the strength attributed to higher dissolution. Increasing holding temperature from 1000 to 1100 degrees C led to a noticeable widening of bond line and increasing boride phases. Eventually, the obtained joint at 1200 degrees C was fully mixed into Inconel 718 base material, although coarser eutectic phases were formed in this sample. Shear strength increased up to 450 MPa by increment in holding temperature from 1000 to 1100 degrees C, while it fell to 433 MPa after TLP bonding at 1200 degrees C. Post-bonding homogenization of samples at 700-900 degrees C caused elimination of eutectic phases in athermally solidified samples, dissolution of diffusion-induced precipitates, and also enhancement of their strength. Fracture studies revealed that the preferred path for crack propagation in the sample containing intermetallic phases was at those eutectic phases.