We study the sintering densification mechanisms of 3D-printed micro-trusses produced by extrusion of inks (consisting of oxide or metallic powders and binder) into continuous, interconnected struts. Upon heat-treatment, the binder is removed, the oxides are reduced to metal powders and the micro-struts are densified by sintering of these metallic powders. Due to low initial powder density, comparably high sintering temperatures and times are needed to achieve near-full densification of the struts resulting in large shrinkage. The sintering process is more complex for cases where a mix of metallic powders (e.g. Fe and Ni) interdiffuses during the sintering process to achieve homogenous alloys (e.g. Fe-Ni). During the heat-treatment, evolution of pore shape, size and fraction, coalescence of powder particles, chemical interdiffusion, and global and local shrinkage are occurring simultaneously. We present here a study, using both metallographic cross-sections and tomographic reconstructions, of the kinetics of, and interactions between, these various processes.