Corrosion behavior of AISI 316L stainless steel surface-modified with NiTi

AISI 316L stainless steel was surface-modified with NiTi using three different methods: (1) laser surface alloying using NiTi powder (LSA-NiTi-powder), (2) laser cladding using NiTi strips (LC-NiTi-strip), and (3) microwave-assisted brazing using NiTi plates (MB-NiTi-plate). These methods are capable of bringing significant improvement in the cavitation erosion resistance as reported elsewhere. The present work aims at studying the corrosion behaviors of these surface-modified stainless steel samples in 3.5% NaCl solution. Cyclic polarization tests reveal that the pitting potentials of the laser-treated samples are comparable to that of the AISI 316L substrate, but the protection potentials and the corrosion potentials are somewhat lower. On the other hand, the corrosion behavior of the brazed sample is similar to that of as-received NiTi, which does not show pitting up to potentials exceeding 1500 mV. Galvanic tests of couples with AISI 316L as one member and the surface-modified sample as the other member show only a small galvanic current density in all the three cases. The ratio of the average galvanic current density to the corrosion current density of the uncoupled anodic member is small (not exceeding 4 in all cases), indicating good compatibility when these techniques are used in local surface modification of AISI 316L substrate.