High-pressure torsion of Ti: synchrotron characterization of phase volume fraction and domain sizes

Rods of grade 2 Ti were processed by Equal-Channel Angular Pressing (ECAP) (phi = 120° at 573 K) employing 2, 4 and 6 passes. The same billets were further deformed by High- Pressure Torsion (HPT) at room temperature, varying both the hydrostatic pressure (1 and 6 GPa) and the number of rotations (n = 1 and 5). The ECAP and HPT samples were studied by synchrotron radiation at DESY-Petra III GEMS line. On the ECAP samples, textures were thus determined while for both ECAP and HPT samples the measurements were further analyzed by MAUD. Domain sizes and phase volume fractions were determined as a function of the radial direction of the samples. Alpha and Omega phases were detected in different amounts depending mostly on hydrostatic pressure and shear deformation. These transition phases can be pressure-induced during HPT processing and the results of Vickers microhardness measurements were related to the processing parameters and to the amounts of these phase

Equal-channel angular pressing: influence of die design on pressure forces, strain homogeneity, and corner gap formation

The results of experiments directed to the optimization of Equal-channel angular pressing (ECAP) die design can be affected by the material response to deformation, thus making difficult to isolate the die performance, particularly with respect to the assessment of strain homogeneity. In the present work, a completely ‘‘inert’’ material was employed for the physical simulation of the ECAP deformation, thus permitting an unequivocal analysis of the die performance. Such material is the Pb–62 %Sn alloy, of which absence of strain hardening, that is,full recrystallization during or after equal-channel angular pressing, was here ascertained. As a consequence, the corner gap effect, a phenomenon known to decrease strain homogeneity, will depend only on die geometry. The study was extended to the case in which the strain distribution depends on both outer (R) and inner (r) curvature radii. Results show that the size of the corner gap is related to the deformation homogeneity of the billet, and the pressing forces are reduced for large outer radii. Emphasis was given to the quantitative measurement of the corner gap size, its relationship with the von Mises strain, and itsdistribution within the ECAP-processed billet, for different R–r combinations

High-Pressure Torsion of Ti: Synchrotron characterization of phase volume fraction and domain sizes

Rods of grade 2 Ti were processed by Equal-Channel Angular Pressing (ECAP) (phi = 120° at 573 K) employing 2, 4 and 6 passes. The same billets were further deformed by High- Pressure Torsion (HPT) at room temperature, varying both the hydrostatic pressure (1 and 6 GPa) and the number of rotations (n = 1 and 5). The ECAP and HPT samples were studied by synchrotron radiation at DESY-Petra III GEMS line. On the ECAP samples, textures were thus determined while for both ECAP and HPT samples the measurements were further analyzed by MAUD. Domain sizes and phase volume fractions were determined as a function of the radial direction of the samples. Alpha and Omega phases were detected in different amounts depending mostly on hydrostatic pressure and shear deformation. These transition phases can be pressure-induced during HPT processing and the results of Vickers microhardness measurements were related to the processing parameters and to the amounts of these phase

Implications of drainage rearrangement for passive margin escarpment evolution in southern Brazil

International audienceAlthough several authors have pointed out the importance of earth surface process to passive margin escarpments relief evolution and even drainage rearrangements, the dynamics of a consolidated capture area (after a drainage network erodes the escarpment, as the one from the Itajai-Acu River) remain poorly understood. Here, results are presented from radar elevation and aerial imagery data coupled with in-situ-produced 1 Be concentrations measured in sand-sized river-born sediments from the Serra Geral escarpment, southern Brazil. The Studied area's relief evolution is captained by the drainage network: while the Itajai-Acu watershed relief is the most dissected and lowest in elevation, it is significantly less dissected in the intermediate elevation Iguacu catchment, an important Parana River tributary. These less dissected and topographically higher areas belong to the Uruguai River catchment. These differences are conditioned by (i) different lithology compositions, structures and genesis; (ii) different morphological configurations, notably slope, range, relief; and (iii) different regional base levels. Along the Serra Geral escarpment, drainage features such as elbows, underfitted valleys, river profile anomalies, and contrasts in mapped chi-values are evidence of the rearrangement process, mainly beheading, where ocean-facing tributaries of the Itajai-Acu River capture the inland catchments (Iguacu and Uruguai). The Be-10 derived denudation rates reinforced such processes: while samples from the Cacador and Araucarias Plateaus yield weighted means of 3.1 +/- 0.2 and 6.5 +/- 0.4 m/Ma respectively, samples from along the escarpment yield a weighted mean of 46.8 +/- 3.6 m/Ma, almost 8 times higher. Such significant denudation rate differences are explained by base-level control, relief characteristics, and the geology framework. The main regional morphological evolutionary mechanism is headward denudation and piracy by the Itajal-Acu River tributaries, As the escarpment moves from east to west, Itajal-Acu River tributaries develop, leading to regional relief lowering and area losses within the Iguacu and Uruguai catchments. Such processes were accelerated since Itajai-Acu tributaries reached into sedimentary and volcanic rocks. From this moment on, Serra Geral became the main hydrographic divide between the ocean- and inland facing-catchments in the area

Microstructure and tensile strength of grade 2 titanium processed by equal-channel angular pressing and by rolling

Commercially pure titanium strengthened by severe plastic deformation constitutes an alternative to the use of complex Ti alloys in many medical or industrial applications. In this research, rods of grade 2 Ti were processed by up to six passes using Equal-channel angular pressing (ECAP) at 573 K followed by cold rolling at room or subzero temperatures. After four passes of ECAP, the grain size was refined down to the submicrometer scale and subsequent rolling led to further refinement. The microstructure was characterized by taking Vickers microhardness measurements and tensile testing was performed both at room temperature and in the temperature range of 573–773 K. The results show that at all temperatures the tensile strength is significantly improved by means of these processing techniques. At room temperature, the ultimate tensile strength of pure Ti after ECAP plus subzero rolling is close to that of the traditional Ti-6Al-4V alloy while maintaining adequate levels of elongation to failure.<br/