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To identify the size effects on the mechanical behavior of microparts is essential for micro-forming. Here, the size effect on the tensile properties of commercial pure titanium foils with thickness ranging from 5 µm to 200 µm has been investigated. The tensile strength, yield strength and work-hardening rate reach a minimum value at the thickness of 30 µm because the main deformation microstructures including dislocations, twins and deformation induced face-centered cubic titanium (fcc-Ti) are different in different foils. The density of deformation twins decreases as the thickness decreases. However, the density of fcc-Ti increases and reaches a maximum value at the thickness of 30 µm. The dominant deformation mechanism is dislocation slip when the thickness is below 20 µm. The yield strength decreases with the decrease in thickness because of the strengthening effect of fcc-Ti being smaller than that of twins when the thickness is above 30 µm. When the ratio of the thickness to grain size is below 5, the yield strength increases with the decrease in thickness due to the large volume fraction of oxides layer on the surface. Based on these, two kinds of constitutive equations have been well established in consideration of the grain size or the ratio of the thickness to grain size. [ABSTRACT FROM AUTHOR]

To identify the size effects on the mechanical behavior of microparts is essential for micro-forming. Here, the size effect on the tensile properties of commercial pure titanium foils with thickness ranging from 5 µm to 200 µm has been investigated. The tensile strength, yield strength and work-hardening rate reach a minimum value at the thickness of 30 µm because the main deformation microstructures including dislocations, twins and deformation induced face-centered cubic titanium (fcc-Ti) are different in different foils. The density of deformation twins decreases as the thickness decreases. However, the density of fcc-Ti increases and reaches a maximum value at the thickness of 30 µm. The dominant deformation mechanism is dislocation slip when the thickness is below 20 µm. The yield strength decreases with the decrease in thickness because of the strengthening effect of fcc-Ti being smaller than that of twins when the thickness is above 30 µm. When the ratio of the thickness to grain size is below 5, the yield strength increases with the decrease in thickness due to the large volume fraction of oxides layer on the surface. Based on these, two kinds of constitutive equations have been well established in consideration of the grain size or the ratio of the thickness to grain size. [ABSTRACT FROM AUTHOR]

The characteristics of shear bands in cold-rolled Ta-2.5W alloy are systematically investigated at different mechanical reduction levels. With increasing strain, the shear bands can appear as in-grain shear bands, trans-granular shear bands and wavy bands. At low strain the crystallographic planar in-grain shear bands are aligned close to the highly stressed slip planes at low strain. As strain increases, the shear bands rotate around the <110> or <111> direction to smaller inclination angles with respect to the rolling direction (RD). Meanwhile, new groups of shear bands are developed. Two groups of in-grain shear bands with a specific fishbone structure appear in the orientations with larger Taylor factor at medium strain. The trans-granular shear bands are formed when the adjacent grains get the continuity of slip planes. Therefore, the frequency of trans-granular shear bands increases with the enhancing of local texture. The wavy bands appear to be a result of sequential necking in the harder γ-fiber and a cooperative flow in the softer α-fiber. Meanwhile, the formation model of the wavy bands is also proposed based on the laminar composites. [ABSTRACT FROM AUTHOR]