Effect of TiC particles on ductility dip cracking susceptibility of Ni-base superalloy

Abstract

Ni-base superalloy FM-52M is mainly used in welded structures of key equipment of nuclear power plants, such as pressure vessels and heat dissipation evaporators. It is prone to form coarse columnar microstructures during welding and has significant ductility dip cracking (DDC) susceptibility. This work attempted to introduce micrometre-sized TiC particles into FM-52M welds to refine the microstructure and alleviate sensitivity to DDC. A Ni–TiC coating with good dispersion and uniformity of TiC particles was first prepared on the substrate by composite electroplating. The TiC particles were then directly introduced into the molten pool during tungsten–inert gas welding. Scanning electron microscopy and electron backscatter diffraction were used to analyse the microstructure of the weld and strain-to-fracture testing was performed to evaluate its DDC sensitivity. The experimental results showed that solidification grains of the weld were obviously refined and its high-temperature mechanical properties were reinforced. The minimum critical strain for DDC increased to approximately 3.5%, and the crack morphology was small and tortuous. Compared with the original material, the microstructure and DDC resistance of the weld were improved by introducing TiC particles.