Effect of deposition strategy on the microstructure and mechanical properties of Inconel 625 superalloy fabricated by pulsed plasma arc deposition

Pulsed plasma arc deposition (PPAD), which combines pulsed plasma cladding with rapid prototyping, is a promising technology for manufacturing near net shape components due to its superiority in cost and convenience of processing. The aim of this study was to investigate the influences of interpass cooling strategy (ICS) and continuous deposition strategy (CDS) on microstructure and mechanical properties of the PPAD Inconel 625 non-ferrous alloy. The as-deposited samples in the two conditions were subjected to the post heat treatment: 980 °C solution treatment + direct aging (STA). The microstructures and mechanical properties of the samples were characterized by means of scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), micro-hardness and tensile testers. It was found that the as-deposited microstructure exhibited homogenous cellular dendrite structure, which grew epitaxially along the deposition direction. The as-deposited microstructure of ICS sample revealed smaller dendritic arm spacing, less niobium segregation and discontinuous finer Laves phase in the interdendritic regions compared to the case of continuous deposition strategy (CDS). The ICS sample exhibited better mechanical properties than CDS sample. After STA heat treatment, a large amount of Laves particles in the interdendritic regions were dissolved, resulting in the reduction of Nb segregation and the precipitation of needle-like δ (Ni3Nb). The tensile and yield strength of the as-deposited samples were improved, while the elongation slightly decreased.

► PPAD Inconel 625 sample deposited with ICS strategy exhibits improved surface quality.
► ICS sample exhibits finer microstructure and improved mechanical properties.
► Higher level γ′ and γ″ phases are precipitated in the ICS sample.
► STA heat treatment reduced the concentration of Nb element.
► STA heat treatment improved the mechanical properties of PPAD Inconel 625.