Hydrodynamic simulations are performed to study Richtmyer-Meshkov instability (RMI) and material ejection at a metal-vacuum interface using a 2D multi-component elastic-plastic hydrodynamic Eulerian code. Effect of material strength on instability development of roughened surface is analyzed, and relationship between amount of ejected material and saturated bubble amplitude is revealed. Finally, based on RMI theory for elastic-plastic solids, theoretical models to describe critical condition of ejecta formation, total amount and maximum velocity of ejecta from unmelted metals are established.