Characterization of Interfacial Microstructure and Mechanical Properties of the Diffusion Bonded CP-Ti to AISI 304L Stainless Steel

This study reports the influence of diffusion kinetics on the interfacial microstructure and its significance in the mechanical properties of the diffusion bonded titanium (Ti) to 304L stainless steel (SS). The surface finished commercially pure Ti (ASTM grade-2), and 304L SS rods were diffusion bonded at three different temperatures viz. 850, 900 and 950 degrees C for 1-h with the imposed pressure of 20 MPa. The partial solubility of Fe, Cr, Ni in Ti and vice versa results in the evolution of brittle intermetallic phases at the joint interface. Using energy-dispersive X-ray spectrometer, the nominal chemical composition of the intermetallic compounds is ascertained, and the phases are confessed with X-ray diffraction studies. The estimation of activation energy and growth constant of the evolved intermetallic phases postulate the susceptibility of lambda + chi formation is more due to the minimum activation energy over other reacting phases. Hardness measurement shows the substantial increase in the hardness at the joint interface (385 +/- 5 HV0.2) in comparison to base metal hardness (150 +/- 2 HV0.2 in Ti and 180 +/- 3 HV0.2 in 304L SS). Transverse tension test reveals the maximum strength of 260 +/- 4 MPa in the bonded specimen at 950 degrees C which is approximately 71% of Ti-base metal tensile strength.