1. A mechanical structure comprising: a crystalline superelastic alloy characterized by an average grain size and exhibiting a martensitic phase transformation resulting from a mechanical stress input greater than a characteristic first critical stress; and a martensitic-phase configuration of the superelastic alloy, including a geometric structural feature of the alloy having an extent that is no greater than about 200 micrometers and that is no larger than the average grain size of the alloy, with martensitic domains of the martensitic-phase configuration extending completely across the geometric structural feature extent, the geometric feature undergoing the martensitic phase transformation without intergranular fracture of the geometric feature.