Sublimation is the transition of a substance from solid to gas without passing through a liquid state. It occurs when the molecules of the solid material escape from the surface and go directly into the gaseous state.  The molecules gain enough energy from heat to break free from the solid state but not enough to enter the liquid state. Cardboard coasters are made of cellulose fibers with low melting and sublimation points. That is why, yes, you can sublimate on cardboard coasters. The print will be transferred to the coaster provided proper airflow and temperature. However, since cardboard is not a flat surface, you might experience some warping of your design.