Room-Temperature Plastic Deformation Behavior of Hard and Brittle Intermetallic Compounds Investigated by Micropillar Compression

Hard materials including carbides, borides, oxides, and intermetallic compounds with complicated crystal structures, have been considered as important strengthening phases in improving mechanical properties of various conventional structural materials by utilizing mainly their extremely high strength. In order to make the best use of the attractive mechanical properties of these hard materials, it is essential to clarify fundamental mechanical properties such as operative deformation modes and their critical resolved shear stress. However, detailed deformation mechanisms of these hard materials are largely unknown mainly because of their extreme brittleness at low temperatures.<br/>Recently, micropillar compression method has been found to be useful in investigating deformation behavior of brittle materials such as Si, GaAs at temperatures far below their ductile to brittle transition temperatures observed for bulk-sized specimens. In our research group, the micropillar compression method has been applied systematically to various hard and brittle materials including transition-metal silicides, Laves phase, mu-phase, sigma phase, transition-metal carbides and so on. We have successfully confirmed that most of them are plastically deformable by the activation of dislocation slip even at room temperature in the micropillar form. In addition to conventional dislocations, atomic-scale scanning transmission electron microscopy (STEM) investigation of dislocation structures developed in plastically deformed micropillar specimens confirmed that non-conventional dislocations of zonal-type and synchroshear-type are activated in sigma-phase and mu-phase at room temperature, respectively. These results clearly indicate the great advantages of the micropillar compression method in investigating inherent deformation behavior of hard and brittle materials with lesser ambiguity.<br/>In the presentation, recent results on plastic deformation mechanisms of various hard and brittle materials including sigma-phase, mu-phase and some carbides investigated by the micropillar compression tests together with the atomic resolution STEM analysis and first-principles calculations of generalized stacking fault energy will be reviewed.