Influence of Strain Rate, Microstructure and Chemical and Phase Composition on Mechanical Behavior of Different Titanium Alloys

Taking three titanium commercial alloys: commercial purity titanium (c.p.Ti), Ti-6-4 (Ti-6(wt.%)Al-4V) and TIMETAL-LCB (Ti-1.5Al-4.5Fe-6.8Mo) as program materials, the influence of phase composition, microstructure and strain rate (varied from 8x10(-4) to 1.81x10(-1)) on the mechanical behavior was studied. The size of the matrix phase (alpha- or beta-grains) and size of alpha + beta intragranular mixture were varied. Such parameter such as tensile toughness (TT) was used for analysis of the mechanical behavior of the materials on tension with different rates. It was found that the TT values monotonically decreased with strain rate, except Ti-6-4 alloy with a globular type of microstructure. In single-phase alpha-material (c.p.Ti), tensile deformation led to the formation of voids at the intragranular cell substructure, and merging of these voids caused the formation of main crack. In two-phase alpha + beta materials, the deformation defects were localized upon tension predominantly near the alpha/beta interphase boundaries, and subsequent fracture had different characters: In Ti-6-4 globular condition fracture started by formation of voids at the alpha/beta interphase boundaries, whereas in all other conditions the voids nucleated at the tips of alpha-lamellae/needles.