Superplastic behavior of fine-grained Al-Mg-Li alloy

The superplastic behavior of fine-grained 1420 Al-Mg-Li alloy was investigated using a modern electron microscopy technique based on automatic analysis of electron backscattered diffraction patterns (EBSD analysis

The influence of defect structures on the mechanical properties of Ti-6Al-4V alloys deformed by high-pressure torsion at ambient temperature

© 2016 Elsevier B.V.The high-pressure torsion method was employed to deform Ti-6Al-4V (TC4) alloy. The ambient temperature and high pressure were used to restrain the grain growth. Clear images showing the microstructure evolution of the deformed TC4 alloys were obtained using SEM, TEM and HRTEM. It was found that the HPT-deformed TC4 alloys contain a high density of dislocations and many defect structures. These dislocations were found to be generated on one or both sides of the elongated grains, and the dislocation lines were able to move across the elongated grains (mostly at ~60°) to form an uncondensed dislocation wall. Although deformation twins did not appear in the alloys deformed at intermediate strains (γ≤23.1), quantities of (10−12) tensile twins containing prismatic stacking faults were observed in the specimens deformed at a much larger plastic strain (γ≥157). The hardness-strain behaviors of the TC4 alloys were similar to those of pure Ti, which have a maximum hardness followed by a strain softening at large strains. In addition, the formation of the omega phase was suppressed due to the dissolution of substitutional Al and V. The alloy that received the highest levels of strain (γ~357) was found to have a nanoscale structure (~49.41 nm) with non-equilibrium GBs, as well as an increased microhardness (~424 HV) and yield strength (σS~960 MPa). The effects of these defect-structures on the mechanical behaviors of a TC4 alloy are mainly determined by their structures’ sizes according to Hall–Petch relationship. However, the effect of this mechanism reduces at large strains due to the existing high-dense dislocations and non-equilibrium grain boundaries

Martensite-to-austenite reversion and recrystallization in cryogenically-rolled type 321 metastable austenitic steel

The annealing behavior of cryogenically-rolled type 321 metastable austenitic steel was established. Cryogenic deformation gave rise to martensitic transformation which developed preferentially within deformation bands. Subsequent annealing in the range of 600 C to 700 C resulted in reversion of the strain-induced martensite to austenite. At 800 C, the reversion was followed by static recrystallization. At relatively-low temperatures, the reversion was characterized by a very strong variant selection, which led to the restoration of the crystallographic orientation of the coarse parent austenite grains. An increase in the annealing temperature relaxed the variant-selection tendency and provided subsequent recrystallization thus leading to significant grain refinement. Nevertheless, a significant portion of the original coarse grains was found to be untransformed and therefore the fine-grain structure was fairly heterogeneous

Grain structure evolution during cryogenic rolling of alpha brass

High-resolution electron backscatter diffraction (EBSD) was used to study grain structure development during cryogenic rolling of Cu-29.5Zn brass. Microstructure evolution was found to be broadly similar to that occurring during rolling at room temperature. Specifically, favorably-oriented grains (Copper {112} and S {123}) experienced profuse deformation twinning followed by extensive shear banding. This eventually produced an ultrafine structure with a mean grain size of ~0.2 m. On the other hand, grains with crystallographic orientations close to Brass {110} and Goss {110} were found to be stable against twinning/shear banding and thus showed no significant grain refinement. As a result, the final structure developed in heavily-rolled material was distinctly inhomogeneous consisting of mm-scale remnants of original grains with poorly developed substructure and ultra-fine grain domains

The influence of defect structures on the mechanical properties of Ti-6Al-4V alloys deformed by high-pressure torsion at ambient temperature

© 2016 Elsevier B.V.The high-pressure torsion method was employed to deform Ti-6Al-4V (TC4) alloy. The ambient temperature and high pressure were used to restrain the grain growth. Clear images showing the microstructure evolution of the deformed TC4 alloys were obtained using SEM, TEM and HRTEM. It was found that the HPT-deformed TC4 alloys contain a high density of dislocations and many defect structures. These dislocations were found to be generated on one or both sides of the elongated grains, and the dislocation lines were able to move across the elongated grains (mostly at ~60°) to form an uncondensed dislocation wall. Although deformation twins did not appear in the alloys deformed at intermediate strains (γ≤23.1), quantities of (10−12) tensile twins containing prismatic stacking faults were observed in the specimens deformed at a much larger plastic strain (γ≥157). The hardness-strain behaviors of the TC4 alloys were similar to those of pure Ti, which have a maximum hardness followed by a strain softening at large strains. In addition, the formation of the omega phase was suppressed due to the dissolution of substitutional Al and V. The alloy that received the highest levels of strain (γ~357) was found to have a nanoscale structure (~49.41 nm) with non-equilibrium GBs, as well as an increased microhardness (~424 HV) and yield strength (σS~960 MPa). The effects of these defect-structures on the mechanical behaviors of a TC4 alloy are mainly determined by their structures’ sizes according to Hall–Petch relationship. However, the effect of this mechanism reduces at large strains due to the existing high-dense dislocations and non-equilibrium grain boundaries

Effect of cryogenic temperature and change of strain path on grain refinement during rolling of Cu-30Zn brass

The effect of cryogenic temperature and change of strain path on grain refinement during the rolling of Cu–30Zn brass was determined. To this end, the material was unidirectionally rolled or cross-rolled to 90% thickness reduction at either ambient or liquid-nitrogen temperatures, and the resulting grain structures and crystallographic textures were determined via electron backscatter diffraction (EBSD) technique. In all cases, grain refinement was found to be governed primarily by twinning and shear banding. Lowering of the rolling temperature to the cryogenic range was found to provide only a minor effect. Cryogenic rolling was thus concluded to impart no practical benefit with regard to grain refinement or property improvement for this material. In contrast, a change of strain path via cross rolling was shown to enhance twinning and shear banding and thus to promote the formation of a relatively homogeneous ultrafine-grain microstructure

Annealing behavior of cryogenically-rolled Cu-30Zn brass

The static-annealing behavior of cryogenically-rolled Cu–30Zn brass over a wide range of temperature (100–900 °C) was established. Between 300 and 400 °C, microstructure and texture evolution were dominated by discontinuous recrystallization. At temperatures of 500 °C and higher, annealing was interpreted in terms of normal grain growth. The recrystallized microstructure developed at 400 °C was ultrafine with a mean grain size of 0.8 μm, fraction of high-angle boundaries of 90 pct., and a weak crystallographic texture