Rutile Electrodes Enhanced with TiO2 Nanoparticles

In this study, a new method of incorporation of TiO2 nano particles into the rutile coating of shielded metal arc welding (SMAW) is presented. In contrast to the conventional method of mixing of nano particles during coating fabrication, the infiltration by immersion method is used, enabling to modify already fabricated elecrodes. To assess the benefits from the incorporated nano particles, different immersion durations were applied: 30 s, 4 and 8 min. Chemical properties of welds obtained with unmodified and modified electrodes, microstructures, tensile properties, hardnesses, SEM of fracture surfaces and EDX analses of non-metallic inclusions were done. It was found that the highest tensile properties were obtained with medium immersion time, due to the grain refinement in the first (reheated zone) and the second pass (columnar zone). This phenomenon is caused by the presence of complex oxides formed around Ti from the dissociated TiO2. This causes the partial replacement of the Widmanstaetten ferrite with acicular ferrite and subsequent grain refinement in the reheated zone. At the highest immersion duration, the specimens exhibited the lowest mechanical properties due to the appearance of large grain allotriomorphic ferrite isles and large non-metallic inclusions that act as void nucleation sites.