Complex Structural Effects in Deformed High-Manganese Steel

The research presented in this paper is part of a larger project concerning deformation behavior, microstructure and mechanical properties of high-manganese steels with different chemical compositions and processed under various conditions. The current investigation deals with the development of microstructure and crystallographic texture of Fe-21.2Mn-2.73Al-2.99Si steel deformed in tension until fracture at ambient temperature. The deformation process of the examined steel turned out to be complex and included not only dislocation slip and twinning but also strain induced phase transformations (g ® e) and (g ® a′). The formation of e-martensite with hexagonal structure was observed within the microstructure of the steel starting from the range of lower strains. With increasing deformation degree, the a′-martensite showing a cubic structure gradually began to form. Attempts have been made to explain the circumstances or conditions for the occurrence of the deformation mechanisms mentioned above and their impact on the mechanical properties. The obtained results indicate that the strength and plastic properties of the steel substantially exceed those of plain carbon steels. Since both, mechanical twinning and the strain-induced phase transformations took place during deformation, it seems that both types of deformation mechanisms contributed to an increase in the mechanical properties of the examined manganese steel.

Rolling Texture of Cu–30%Zn Alloy Using Taylor Model Based on Twinning and Coplanar Slip

A modified Taylor model, hereafter referred to as the MTCS(Mechanical-Twinning-withCoplanar-Slip)-model, is proposed in the present work to predict weak texture components in the shear bands of brass-type fcc metals with a twin–matrix lamellar (TML) structure. The MTCS-model considers two boundary conditions (i.e., twinning does not occur in previously twinned areas and coplanar slip occurs in the TML region) to simulate the rolling texture of Cu–30%Zn. In the first approximation, texture simulation using the MTCS-model revealed brass-type textures, including Y {1 1 1}⟨1 1 2⟩ and Z {1 1 1}⟨1 1 0⟩ components, which correspond to the observed experimental textures. Single orientations of C (1 1 2)[1 ¯ 1 ¯ 1] and S’ (1 2 3)[4¯ 1¯ 2] were applied to the MTCS-model to understand the evolution of Y and Z components. For the Y orientation, the C orientation rotates toward T (5 5 2)[1 1 5] by twinning after 30% reduction and then toward Y (1 1 1)[1 1 2] by coplanar slip after over 30% reduction. For the Z orientation, the S’ orientation rotates toward T’ (3 2 1)[2 1 ¯4¯] by twinning after 30% reduction and then toward Z (1 1 1)[1 0 1¯] by coplanar slip after over 30% reduction.

Hot Deformation Behavior of a Beta Metastable TMZF Alloy: Microstructural and Constitutive Phenomenological Analysis

A metastable beta TMZF alloy was tested by isothermal compression under different conditions of deformation temperature (923 to 1173 K), strain rate (0.172, 1.72, and 17.2 s−1), and a constant strain of 0.8. Stress–strain curves, constitutive constants calculations, and microstructural analysis were performed to understand the alloy’s hot working behavior in regards to the softening and hardening mechanisms operating during deformation. The primary softening mechanism was dynamic recovery, promoting dynamic recrystallization delay during deformation at higher temperatures and low strain rates. Mechanical twinning was an essential deformation mechanism of this alloy, being observed on a nanometric scale. Spinodal decomposition evidence was found to occur during hot deformation. Different models of phenomenological constitutive equations were tested to verify the effectiveness of flow stress prediction. The stress exponent n, derived from the strain-compensated Arrhenius-type constitutive model, presented values that point to the occurrence of internal stress at the beginning of the deformation, related to complex interactions of dislocations and dispersed phases.

Microstructure and Mechanical Properties Change with Cold Rolling of New Ti-13Nb-1.5Ta-3Mo Alloy

In this paper, a new metastable Titanium alloy in the Ti-Nb-Ta-Mo system has been successfully produced using both the d-electron and Moeq concept. The influence of cold rolling on the microstructure and hardness was investigated. The alloy was fabricated by arc melting, cold rolled up to 90% reduction in thickness and characterized using X-ray diffraction (XRD), optical microscope and Vickers microhardness. The XRD peaks depicted both β and α′′ phases in all the cold rolled specimens. The hardness of the alloy increased with increasing cold rolling reduction thickness. An excellent plasticity (≥ 65%) and compressive strength up to (2.9 GPa) was achieved with low Young’s modulus (31 GPa) and no failure or crack on the alloy. Also, the alloy demonstrated a high compressive true strength coefficient (k ≈1426 MPa) along with improved strain hardening index (n ≈ 0.41). Based on the XRD, optical microscope and microhardness indentation micrographs, the deformation mechanism of Ti-13Nb-1.5Ta-3Mo was found to be a combination of stress induced transformation, mechanical twinning and slipping.

Deformation Twinning Induced High Tensile Ductility of a Gradient Nanograined Cu-Based Alloy

We investigated the tensile properties of gradient nanograined Cu and CuAl samples prepared by plastic deformation. Tensile tests showed that the gradient nanograined Cu-4.5Al sample exhibits a uniform elongation of ~22% without any cracks, while the uniform elongation of the gradient nanograined Cu sample is only ~18%. Numerous mechanical twinning retards the softening of the nanograins and accommodates a high tensile ductility in the gradient nanograined Cu-4.5Al sample. This work indicates that mechanical twinning is a potential deformation mechanism to achieve high tensile ductility of nanograined materials.

Surface and Subsurface Analysis of Stainless Steel and Titanium Alloys Exposed to Ultrasonic Pulsating Water Jet

This article deals with the effect of periodically acting liquid droplets on the polished surfaces of AISI 316L stainless steel and Ti6Al4V titanium alloy. These materials were exposed to a pulsating water jet produced using an ultrasonic sonotrode with an oscillation frequency of 21 kHz placed in a pressure chamber. The only variable in the experiments was the time for which the materials were exposed to water droplets, i.e., the number of impingements; the other parameters were kept constant. We chose a low number of impingements to study the incubation stages of the deformation caused by the pulsating water jet. The surfaces of the specimens were studied using (1) confocal microscopy for characterizing the surface profile induced by the water jet, (2) scanning electron microscopy for detailed surface observation, and (3) transmission electron microscopy for detecting the changes in the near-surface microstructure. The surface described by the height of the primary profile of the surface increased with the number of impingements, and was substantially more intense in the austenitic steel than in the Ti alloy. Irregular surface depressions, slip lines, and short cracks were observed in the Ti alloy, whereas pronounced straight slip bands formed in the austenitic steel. The dislocation density near the surface was measured quantitatively, reaching high values of the order of 1014 m−2 in the austenitic steel and even higher values (up to 3 × 1015 m−2) in the Ti alloy. The origins of the mentioned surface features differed in the two materials: an intense dislocation slip on parallel slip planes for the Ti alloy and mechanical twinning combined with dislocation slip for the austenitic steel.

Long-term (7 Ma) strain fluctuations within the Dead Sea transform system from high-resolution U-Pb dating of a calcite vein

The onset of the Dead Sea transform has recently been reevaluated by U-Pb age-strain analyses of fault-related calcite taken from several fault strands along its main 500-km-long sector. The results suggest that the relative motion between Africa and Arabia north of the Red Sea was transferred northward to the Dead Sea transform as early as 20 Ma and along a ∼10-km-wide deformation zone that formed the central rift with contemporaneous bounding sinistral motion. The Gishron fault is the western bounding fault with normal and sinistral fault offsets that placed Proterozoic crystalline rocks and a cover of Cambrian sandstones in fault contact with Cretaceous-Eocene carbonates. Fault-related calcite veins are common in the Gishron fault zone, and we report the results of a detailed study of one sample with nine calcite fillings. Low fluid inclusion entrapment temperatures <50 °C, stable isotopes values of −3.3−0‰ (δ13C) and −15 to −13‰ (δ18O), and low rare earth element (REE) concentrations within the nine calcite fault fillings indicate that a local, meteoric fluid fed the Gishron fault zone over ca. 7 Ma at depths of <2 km. Laser ablation U-Pb ages within the thin section range from 20.37 Ma to 12.89 Ma and allow a detailed fault-filling chronology with the oldest calcite filling in the middle, younging outward with shearing between the oldest eight zones, all of which are finally crosscut by a perpendicular (E-W) vein. All nine calcite fillings have unique mechanical twinning strain results (n = 303 grains). Shortening strain magnitudes (−0.28% to −2.8%) and differential stresses (−339 bars to −415 bars) vary across the sample, as do the orientations of the shortening (ε1) and extension (ε3) axes with no evidence of any twinning strain overprint (low negative expected values). Overall, the tectonic compression and shortening is sub-horizontal and sub-parallel to the Gishron fault (∼N-S) and Dead Sea transform plate boundary. Most strikingly, the 7 m.y. period of vein growth correlates exactly with the timing of fault activity as evident within the 10-km-wide deformation zone in this evolving plate boundary (between 20 Ma and 13 Ma).