In the sintering phase of additive manufacturing of micro-scale metallic components, observations indicate that a hitherto unknown long-range mass transport mechanism exists [1]. To study the mechanisms on the mesoscale, a computational phase field model for moving interfaces is indicated, which should include stress and concentration driven diffusion through bulk and surfaces, as well as the growth of new lattice. In the early stages of sintering, the gas flows out of the domain, while in the later stages, when pores cease to percolate, the gas is compressed in closed pores. Modeling of solids with diffusion requires formulation of lattice continuum [2], whereby the material is represented by lattice sites (as opposed to the traditional mass continuum where the material is identified with mass). Traditional solid mechanic theories (elasticity and plasticity) are, in fact, lattice continua, although this is not emphasized – in the absence of diffusion, mass and lattice motions are indistinguishable. With gas represented by mass continuum, we are faced with the problem of formulating the phase field model which encompasses heterologous continua. Specifically, the unique continuous velocity/displacement fields that characterize the phase field formulation must undergo rapid transitions at (diffuse) interfaces. These transitions account for lattice growth rates of grains which are diffusion-controlled and defined relative to the lattice velocity. These issues occur at interfaces between both heterologous and homologous (lattice-lattice) continua. Here, we address the following questions: Do the standard balance laws assure that the computational model satisfies the interface conditions, or, is the explicit enforcement needed? How are such conditions to be enforced in a computational setting? We present preliminary computational results and theoretical analysis. REFERENCES [1] Ritchie, S., Kovacevic, S., Deshmukh, P., Mesarovic, S.Dj., Panat, R. 2023 Shape distortion in sintering results from nonhomogeneous temperature activating a long-range mass transport. Nature Communications 14, 2667. [2] Mesarovic, S.Dj. 2016 Lattice continuum and diffusional creep. Proc. R. Soc. A 472, 20160039.