Examination of the distribution of the tensile deformation systems in tension and tension-creep of Ti-6Al-4V (wt.%) at 296 K and 728 K

Abstract

The deformation behaviour of an α + β Ti-6Al-4V (wt.%) alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Tensile experiments were performed at 296 and 728 K (~0.4Tm), while a tensile-creep experiment was performed at 728 K and 310 MPa (σ/σ ys = 0.74). The active deformation systems were identified using electron backscattered diffraction-based slip-trace analysis and SEM images of the specimen surface. The distribution of the active deformation systems varied as a function of temperature. Basal slip deformation played a major role in the tensile deformation behaviour, and the relative activity of basal slip increased with increasing temperature. For the 296 K tension deformation, basal slip was less active than prismatic slip, whereas this was reversed at 728 K. Twinning was observed in both the 296 and 728 K tension experiments; however, no more than 4% of the total deformation systems observed was twins. The tension-creep experiment revealed no slip traces, however grain boundary ledge formation was observed, suggesting that grain boundary sliding was an active deformation mechanism. The results of this work were compared with those from previous studies on commercially pure Ti, Ti-5Al-2.5Sn (wt.%) and Ti-8Al-1Mo-1V (wt.%), and the effects of alloying on the deformation behaviour are discussed. The relative amount of basal slip activity increased with increasing Al content. IntroductionCompared with other structural metallic metals based on iron (Fe), nickel (Ni), aluminium (Al), and magnesium (Mg), titanium (Ti) has advantages of higher specific strength and exceptional corrosion resistance with a low density (ρ) of~4.5 g/cm 3 . Although Mg exhibits a density of~1.8 g/cm 3 , the disadvantages of low corrosion resistance, low melting point (650°C, 923 K) and relatively low yield strength (YS) make it less suitable than Ti for many structural applications. Al (ρ~2.7 g/cm 3 ) also exhibits the drawbacks of a low melting temperature (660°C, 933 K) and a low YS. Fe and Ni can overcome these disadvantages but the densities are nearly twice that of Ti. Thus, Ti and Ti alloys are currently employed in a variety of applications, including armor and

The tensile and tensile-creep deformation behavior of Ti–8Al–1Mo–1V(wt%)

“…Thus, dislocation slip was the dominant deformation mechanism in the tensile-creep test of CP Ti, and when slip occurred, prismatic slip was preferred. In contrast, no slip traces were observed during the 455 o C-310MPa creep test of Ti-6Al-4V [27], and grain boundary sliding was clearly a dominant deformation mechanism to accommodate plastic deformation. In the 455 o C-250MPa creep test of Ti-5Al-2.5Sn [4,26], only ~10% of the total grains exhibited slip traces, where 78% of deformation systems were basal slip and 16% of the deformation systems were prismatic slip.…”

“…deformed at both 25 o C and 455 o C, twinning accounted for no more than 4% of the deformation systems [27]. For Ti-8Al-1Mo-1V no twinning was observed.…”

“…creep deformation of Ti-6Al-4V [27], grain boundary sliding appeared to be the primary deformation mechanism rather than dislocation slip. Although the ratio of the applied creep stress to the YS was similar in CP Ti (0.73), Ti-5Al-2.5Sn (0.76), Ti-8Al-1Mo-1V (0.6), and Ti-6Al-4V (0.74), dislocation slip, rather than grain boundary siding, was the dominant deformation mechanism in CP Ti creep.…”

“…Ti-8Al-1Mo-1V to that for Ti-6Al-4V [27], CP Ti [4,26], and Ti-5Al-2.5Sn [4,26]. During the elevated-temperature tensile-creep tests, the relative activity of dislocation slip and grain boundary sliding varied from material to material.…”

In Situ Scanning Electron Microscopy Observations of Contraction Twinning and Double Twinning in Extruded Mg-1Mn (wt.%)

“…Further details of this in situ testing technique and deformation characterization method can be found elsewhere. [23][24][25][26][27][28][29][30] …”