Improvement of mechanical properties and corrosion resistance for wire arc additive manufactured nickel alloy 690 by adding TiC particles

Abstract

Nickel alloy 690 (Ni690) were fabricated by wire arc additive manufacturing (WAAM) with three kinds of TiC particles adding contents (no TiC addition, 0.5 wt% TiC, 1.0 wt% TiC) based on cold metal transfer (CMT) technology. The effects of TiC particles adding content on the microstructure, mechanical properties and corrosion resistance were investigated. After adding 1.0 wt% TiC particles, the average length of the γ grains decreased from 301 ± 61 µm to 114 ± 15 µm and the structure of grains changed from columnar dendrite into equiaxed dendritic at the top of each layer, which is results of the heterogeneous nucleation and increase of constitutional supercooling caused by TiC particles. The difference between horizontal and vertical mechanical properties of WAAM Ni690 component disappeared because the heterogeneous nucleation caused by TiC particles prevented the epitaxial growth. The ultimate tensile strength of the WAAM 1.0TiC-Ni690 component reached 590 MPa in both directions, which increased 10 % compared with no TiC addition. The improvement of mechanical properties was owing to the grain refinement and the formation of reinforcing TiC/(Ti, Nb)C second-phase particles. The potentiodynamic polarization tests showed that the improved corrosion resistance with the increased content of TiC particles. The electrochemical impedance spectroscopy (EIS) tests results showed that due to the refined γ columnar grains providing more nucleation sites, a denser and thicker passive film was formed, which improved the corrosion resistance. The composition of the passive film was analyzed by X-ray photoelectron spectroscopy (XPS). The results reflected the more content of oxides and hydroxides of Cr in the passive film of WAAM 1.0TiC-Ni690 sample represented the denser passive film and better corrosion resistance.