Effects of WC Addition on the Microstructure and Mechanical Properties of Inconel 625 Alloys Fabricated by Laser Powder Bed Fusion

The addition of WC to metallic materials has been proved to be an effective way to improve the mechanical strength using fusion-based additive manufacturing, such as laser power-bed fusion (LPBF). What happened to WC particles is a key to understand it role in the strengthening mechanism during LPBF. This study investigated the whereabout of WC powders when in-situ added to IN625 alloys and its effect on the microstructure and mechanical properties of the samples fabricated by LPBF. It was found that there are basically three whereabouts of WC: decomposed products of C and W₂C, remained WC, and dissolved WC. The former significantly promotes nanoprecipitation along the solidification cellular boundaries, which is coincident with dislocation walls. The addition of WC refined the size of solidification cells and grains, and weaken the columnar morphology of the grain as well. The yield strength for the samples when added 5% and 10% WC reaches 763.2 MPa and 1038.7 MPa, respectively. WC particles play an indirect role in improving strength via decomposition of WC and promoting nano-precipitate along cellular boundaries. Among the various strengthening mechanisms, nano-precipitation becomes predominant as WC increase, which accounts for 41.6% of the increment in yield strength.

Graphical abstract