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In this work, Vickers microhardness and spherical nanoindentation (NI) experiments—with hemispherical radii, R, of 13.5, 5, and 1.4 μm—were used to explore the room temperature deformation behavior of poled barium titanate (BaTiO3) single crystals with two orientations: (001) and (110). At 209±11 and 193±11 GPa, Young’s moduli of the (001) and (110) surfaces, respectively, were comparable. The (001) surface deforms elastically, before a pop-in event, followed by a strain-hardening regime. The pop-in stresses are stochastic in nature and can be described by Weibull statistics. The (110) surface deforms elastically, then plastically at lower stresses, before cracks are initiated, beyond which the strain-hardening regime is almost identical to that of the (001) surface. This three-regime behavior of the (110) surface was confirmed by postindentation scanning electron microscope micrographs. This work confirms that the room temperature deformation of single crystal BaTiO3 occurs by glide on the {110} slip planes that are also the cleavage planes. Furthermore fully reversible reproducible stress/strain loops were observed and attributed to the formation and annihilation of fully reversible dislocation loops, whose threshold stresses were a function of the domain size that forms under the various indenters. The domain sizes appear to scale with R and are believed to be responsible for the NI size effect observed. [ABSTRACT FROM AUTHOR]

Tensile ductility of the Ti-based composites, which consist of a β-Ti phase surrounded by ultrafine structured intermetallics, is tunable through the control of intermetallics. The two Ti-based alloys studied exhibit similar compressive yield strength (about 1000MPa) and strain (about 35%-40%) but show a distinct difference in their tensile plasticity. The alloy Ti71.8Nb14.1Ni7.4Al6.7 fractures at the yield stress while the alloy Ti71.8Nb14.1Co7.4Al6.7 exhibits about 4.5% of tensile plastic deformation. To clarify the effect of microstructure on the deformation behavior of these alloys, tensile tests were carried out in the scanning electron microscope. It is shown that the distribution as well as the type of intermetallics affects the tensile ductility of the alloys. [ABSTRACT FROM AUTHOR]

The recent interest in size-dependent deformation of micro- and nanoscale materials has paralleled both technological miniaturization and advancements in imaging and small-scale mechanical testing methods. Here we describe a quantitative in situ nanomechanical testing approach adapted to a dual-beam focused ion beam and scanning electron microscope. A transducer based on a three-plate capacitor system is used for high-fidelity force and displacement measurements. Specimen manipulation, transfer, and alignment are performed using a manipulator, independently controlled positioners, and the focused ion beam. Gripping of specimens is achieved using electron-beam assisted Pt-organic deposition. Local strain measurements are obtained using digital image correlation of electron images taken during testing. Examples showing results for tensile testing of single-crystalline metallic nanowires and compression of nanoporous Au pillars will be presented in the context of size effects on mechanical behavior and highlight some of the challenges of conducting nanomechanical testing in vacuum environments. [ABSTRACT FROM AUTHOR]

A general nano-mechanical test platform capable of performing variable temperature and variable strain rate testing in situ in the scanning electron microscope is described. A variety of test geometries are possible in combination with focused ion beam machining or other fabrication techniques: indentation, micro-compression, cantilever bending, and scratch testing. The system is intrinsically displacement-controlled, which allows it to function directly as a micro-scale thermomechanical test frame. Stable, elevated temperature indentation/micro-compression requires the indenter tip and the sample to be in thermal equilibrium to prevent thermal displacement drift due to thermal expansion. This is achieved through independent heating and temperature monitoring of both the indenter tip and sample. Furthermore, the apex temperature of the indenter tip is calibrated, which allows it to act as a referenced surface temperature probe during contact. A full description of the system is provided, and the effects of indenter geometry and of radiation on imaging conditions are discussed. The stabilization time and temperature distribution throughout the system as a function of temperature is characterized. The advantages of temperature monitoring and thermal calibration of the indenter tip are illustrated, which include the possibility of local thermal conductivity measurement. Finally, validation results using nanoindentation on fused silica and micro-compression of <100> silicon micro-pillars as a function of temperature up to 500 °C are presented, and procedures and considerations taken for these measurements are discussed. A brittle to ductile transition from fracture to splitting then plastic deformation is directly observed in the SEM for silicon as a function of temperature. [ABSTRACT FROM AUTHOR]