Modeling and characterization of texture evolution in twist extrusion

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Effects of Defect Development During Displacive Austenite Reversion on Strain Hardening and Formability

Martensite that is mechanically induced from metastable austenite can be reversed to austenite upon annealing. The reversion transformation can be either diffusive or displacive, and the defect substructure development, in either case, has mechanical consequences. Here, to better understand the effects of microstructure development during displacive phase transformations, we focus on the influence of the initial plastic deformation on the austenite reversion (α′ → γ) in a transformation-induced plasticity-maraging steel. The phase transformation kinetics and the developing defect structure within the reversed γ phase are characterized by carrying out differential scanning calorimetry measurements, electron-backscattered diffraction, and electron channeling contrast imaging analyses. The resulting mechanical behavior is investigated by uniaxial and biaxial tension experiments. These investigations demonstrate that the defect development during sequential deformation-annealing treatments can help increase the overall strain hardening capacity of the alloy, which in turn increases the accumulative uniform elongation, and the formability. While the necking can be progressively delayed to higher strain levels following such treatments, the local fracture strain apparently cannot be, due to damage accumulation

Strengthening mechanisms in nanostructured Al/SiCp composite manufactured by accumulative press bonding

The strengthening mechanisms in nanostructured Al/SiCp composite deformed to high strain by a novel severe plastic deformation process, accumulative press bonding (APB), were investigated. The composite exhibited yield strength of 148 MPa which was 5 and 1.5 times higher than that of raw aluminum (29 MPa) and aluminum-APB (95 MPa) alloys, respectively. A remarkable increase was also observed in the ultimate tensile strength of Al/SiCp-APB composite, 222 MPa, which was 2.5 and 1.2 times greater than the obtained values for raw aluminum (88 MPa) and aluminum-APB (180 MPa) alloys, respectively. Analytical models well described the contribution of various strengthening mechanisms. The contributions of grain boundary, strain hardening, thermal mismatch, Orowan, elastic mismatch, and load-bearing strengthening mechanisms to the overall strength of the Al/SiCp microcomposite were 64.9, 49, 6.8, 2.4, 5.4, and 1.5 MPa, respectively. Whereas Orowan strengthening mechanism was considered as the most dominating strengthening mechanism in Al/SiCp nanocomposites, it was negligible for strengthening the microcomposite. Al/SiCp nanocomposite showed good agreement with quadratic summation model; however, experimental results exhibited good accordance with arithmetic and compounding summation models in the microcomposite. While average grain size of the composite reached 380 nm, it was less than 100 nm in the vicinity of SiC particles as a result of particle-stimulated nucleation mechanism.The authors acknowledge financial support from CICYT (Spain) under program MAT2012-38962-C03-01 and the Ministry of Science, Research and Technology of Iran