Deformation behavior and the mechanism of micro-scale Ti-10V-2Fe-3Al pillars in compression

Ti and its alloys have potential application in micro-electromechanical systems (MEMS) for its excellent mechanical properties. The strength of micro-and nano-scale Ti and its alloys has been proven significantly increased as the sample size decreased, which is known as the "size effect", when dislocation and twinning are dominant plastic deformation modes. Martensitic transformation is an important plastic deformation mode in the Ti alloys. However, there is a limited research on the martensitic transformation in small-scale. Therefore, the study on mechanical behavior and deformation mechanism of [011]-oriented Ti-10V-2Fe-3Al (Ti1023) single crystal micropillars in a size range of 0.3~2.0 μm were investigated under uniaxial compression. The results show that Ti1023 micropillars exhibit smooth stress-strain curves in the regime of plastic deformation without a conventional strain burst phenomenon in the submicron pillars. It means continuous plastic strain hardening. The relationship between the yield stress (σ_0.2), the stress for stress-induced martensite phase (SIM) transformation (σ_cm) and the sample size can be expressed in the forms of σ_0.2∝d_-0.18 and σ_cm∝d_-0.28, respectively. Strain hardening exponent (n) in-creases with decreasing micropillar size. SEM examination together with crystallography analysis show that {112}<111> slip predominates plastic deformation mode in the Ti1023 micropillars. Transmission electron microscopy (TEM) observation of microstructures in the deformed and undeformed micropillars indicate that both nanoscale athermal ω particles and SIM phase α″ impede dislocation movement, and prohibit the formation of tangled dislocations in a collective, avalanche-like way resulting in strain bursts.