Lin Xiao

The mechanical behaviors and deformation mechanisms of solution treated and 450°C aged Ti-55531 alloy microsamples are investigated by the micro-compression and micro-bending. The results show that the dislocation slip is a concentrated movement in the solution treated microsamples which containing nanoscale ω phase. Under the tensile and compressive stress, there were serious strain bursts occurred in the plastic deformation of solution treated microsamples. But the dislocation slip is transmit at the phase interface in the 450°C aged microsamples which containing high density of α phase. The deformation behavior exhibits high strength and excellent stability in the micro-compression and micro-bending process. The different mechanical behaviors and deformation mechanisms of Ti-55531 alloy containing different second phase have significant guidance for tailoring the microstructure and mechanical properties.Key words: Titanium, Micro-compression, Micro-bending, Dislocation, Mechanical behavior

With the increase of time, the shrinkage of materials at fixed temperature could enhance the failure of fasteners. We report a potential way to alter the volume/length of alloy automatically through isothermal aging due to pseudospinodal decomposition mechanism. The volume of Ti-10V-2Fe-3Al alloy first shrunk and then expanded during isothermal aging at 550 °C. It can fit tightly and make up for volume loss. Transmission electron microscopy observation exhibits no obvious coarsening of intragranular α phase with the increasing time. However, composition evolution with time shows a gradual change through energy dispersive spectrometer analysis. The result shows that β stabilizers, V and Fe, are prone to diffuse to the β matrix, while α stabilizers, Al, prefer to segregate to the α phase. First principle calculations suggest that the structure transition for β to α cause the first decrease of volume, and the diffusion of V, Fe and Al is the origin of the later abnormal increase of volume.

Excellent stability of plasticity and high strength are acquired in Ti55531 alloy micropillars via introducing a high density of deformable nanoscale α phase into a β matrix. The yield strength of the pillars is as high as 2.26 GPa irrespective of pillar sizes ranging from 6 to 0.3 μm, which is high enough to activate dislocation slip both in ductile α precipitates and the β matrix. The harmony slip model was proposed to interpret slip transmission between the nanoscale α phase and the divided β matrix, and both α and β accommodate their individual plasticity during compression. This results in an excellent combination of high strength and stable plasticity in Ti55531 alloy micron-to submicron pillars. The results highlight the novel strengthening and toughening mechanisms of nanostructured alloys and a specific type of microstructure that exhibits stable plasticity for nano/microdevices.