Two metallurgically incompatible materials, titanium grade 2 and type 304L stainless steel (SS) were joined through explosive welding for applications in nitric acid service. The morphology and microstructure of the bonded interface were examined using a scanning electron microscope (SEM) and an optical microscope. Typical wavy interface along with solidified melted zones at wave vortexes were observed. Various intermetallic phases, having high hardness, were shown to be formed in these solidified melted zones. Elemental distribution in these intermetallic phases were established using SEM coupled with energy dispersive spectroscopy (EDS). Low corrosion rates were observed after exposure of the weld specimens in 14.5 M and 4 M HNO3 boiling solutions. In addition, potentiodynamic polarization tests in 4 M HNO3 solution have been performed at different surfaces at the plane of the welded interface by successive material removal by grinding from 304L SS through weld to titanium. Despite the presence of different intermetallic phases at the test surfaces, it was found that the current densities in the passive regime of potentials were low. The morphological examination of the tested surfaces revealed that corrosion attack was mainly along the boundaries between SS / intermetallic phases, Ti / SS and along the pre-existing cracks in the intermetallic phases. No corrosion attack was observed along the boundaries between Ti and intermetallic phases.

In the present study, laser surface melting (LSM) of 304L stainless steel (SS) was performed using 250 W pulse Nd: YAG laser which resulted in a 250 µm thick melted layer with refined microstructure on the surface. Potentiostatic polarisations at various potentials in the transpassive regime in 6 M HNO 3 solution at 95°C were used to quantify the IGC rate. The transpassive dissolution rate was significantly reduced after LSM. The pitting corrosion susceptibility was assessed by potentiodynamic polarisation in 3.5 wt-% NaCl solution. LSM resulted in an increase in pitting potential. Following electrochemical tests, sample surfaces were examined using optical and scanning electron microscopes besides a 3-D optical profilometer. The depths of IGC attack and pit were significantly reduced after LSM. The improvement in resistance to pitting corrosion and transpassive dissolution was attributed to the elimination of inclusions and impurity segregation at the grain boundaries brought about by LSM.