A method includes issuing a state change fluid into an internal passage of an additively manufactured article and causing the state change fluid to change from a first state having a first viscosity to a second state that is either solid or has a second viscosity that is higher than the first viscosity within the internal passage. The method can also include causing the state change fluid to change back from the second state to the first state and flushing the state change fluid from the internal passage to remove residual powder from the additively manufactured article.