In-situ alloyed CoCrFeMnNi high entropy alloy: microstructural development in laser powder bed fusion

In-situ alloying has the potential to combine the compositional flexibility of high entropy alloys (HEAs) and the advanced forming capability of laser powder bed fusion (LPBF). This study fundamentally investigated the elemental homogenisation and grain development in the in-situ alloying process of CoCrFeMnNi HEA, by analysing the basic units, i.e., tracks and layers, and introducing Mn as an alloying element to the base CoCrFeNi HEA. Different modelling methods were employed to predict meltpool dimensions, and the results indicated the dependence of the modelling on practical meltpool modes. Delimitation of elemental distribution was found in keyhole meltpools since an intensive flow was generated due to recoil pressure. The homogeneity of in-situ alloyed Mn in single tracks was insufficient whether operated in conduction mode or keyhole mode, which required remelting from adjacent tracks and following layers to promote homogenisation significantly. The preferred orientation in single tracks along scanning directions changed from <001> to <101> as the scanning speed increased, although the cross-sections were similar in size with identical linear energy density. Such preference can be inherited during the printing process and lead to different textures in three-layer samples. It was also observed that applying hatch spacing smaller than a half meltpool width could coarsen the grains in a layer. The results from this study provide structure-parameter correlations for future microstructural tailoring and manipulation.