High cycle fatigue of ARMCO iron severely deformed by ECAP

The high-cycle fatigue behavior of ARMCO iron severely deformed by Equal Channel Angular Pressing (ECAP) at room temperature through route Bc until 8 passes, with an average grain size of ~365 nm, was studied and compared with the same material in the annealed state with an average grain size of ~72 µm. The fatigue limit of the 8 passes ECAPed sample increased with respect to the annealed material by more than 250% rising from 274 MPa to 717 MPa. Striations and dimpled relief were observed on the fracture surfaces of the fatigued ultrafine and coarse grain fatigue samples. The microstructure was characterized by Electron Backscattered Diffraction (EBSD) before and after the fatigue tests and it was observed in both samples an increment in the fraction of Low Angle Grain Boundaries (LAGB) at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was done. This study shown a preferential orientation towards the ¿ fiber for both conditions.Peer ReviewedPostprint (author's final draft

On the microstructure and texture of Cu-Cr-Zr alloy after severe plastic deformation by ECAP

Samples of a commercial Cu-1Cr-0.1Zr (wt.%) alloy were subjected to severe plastic deformation at room temperature using equal-channel angular pressing (ECAP) up to 16 passes via route Bc. The microstructure and texture of the processed samples were analyzed through electron backscatter diffraction (EBSD). Most of the grains were more or less inclined in the direction of shearing (45° from the extrusion direction) and substantially refined. The deformation structure evolved from elongated grains to a duplex equiaxed-elongated microstructure upon straining. The fraction of high angle boundaries gradually increased with the number of passes up to 70%. The texture after ECAP was mainly of ECAP shear type whose components shifted slightly from their ideal positions. A net strengthening and stabilization of the B/View the MathML sourcecomponents were observed.Peer ReviewedPostprint (author's final draft

Microstructural and mechanical study in the plastic zone of ARMCO iron processed by ECAP

Plastic deformation of ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen (i.e., 1, 4, 8, and 16 ECAP passes) following route Bc was investigated by analyzing its microstructure and the stress-strain curves obtained after tensile tests at different levels of deformation. Three values of deformation (two in the plastic region taking into account the modified Crussard-Jaoul analysis and one after failure) were considered. Fractions of LAGB and HAGB, grain size and grain aspect ratio were calculated and compared for the different ECAP passes and tensile deformation levels. The dislocation density evolution calculated by the Bergström model for both the tensile curves and the ECAP curve showed a higher increase in the amount of dislocations during the initial stages of deformation than at higher values of deformation due to higher probabilities of dislocations annihilation. The strain hardening exponents calculated via the Bergström model for each ECAP pass shows that there is a continuous decrease in the strain hardening capacity until the eighth pass where a small increase with a subsequent stabilization was found. The dislocation densities calculated by the Estrin model presented a good correlation with values reported in bibliography for iron especially with those calculated by X-ray diffraction. This latter model predicted well the strain hardening evolution for stages III, IV and V for ARMCO iron processed by ECAP, where the main increments in hardening for stages IV and V were coming from the cell interiors.Preprin

Effect of heat treatments on the mechanical and microstructural behavior of a hypoeutectic Al alloy obtained by laser power bed fusion

Large gains in strength and ductility are of little significance if the material’s anisotropy is high. Therefore, improving the mechanical properties and reducing the anisotropy of Al alloys obtained by additive manufacturing is a topic of growing interest. This manuscript examines the effect of distinct heat treatments on the mechanical, anisotropic, and microstructural behavior of a hypoeutectic, almost eutectic, AlSi11Cu alloy obtained by laser powder bed fusion (L-PBF). The microstructural characterization revealed an Al matrix surrounded by a Si-rich network, forming a coral-like pattern with a heterogeneous combination of columnar and equiaxed grains. The texture indicated that the columnar grains were preferentially oriented towards the building direction with strong Cube and Goss components. Different strength-ductility ratios were obtained following the annealing and solution heat treatments at different temperatures (200 °C–550 °C) with a holding time of 1 h. In terms of grain size and dislocation density, no significant changes were found in the microstructure, suggesting that grain size and dislocation strengthening mechanisms are not highly affected by the heat treatments. In addition, the Si-enriched network remained interconnected until 300 °C. At higher temperatures, this interconnection was lost, giving rise to large Si particles depleting the Si content in solid solution in the Al matrix. Digital image correlation maps revealed that deformation fields were more homogeneous when the cellular structure disappeared. The visco-plastic self-consistent model showed that when applying the load at 30° in the building direction (BD), the largest tensile strength was generated, whereas the lowest strength was obtained when the load was parallel to the BD. Heat treatments for 1 h holding time were found to be efficient in reducing the Lankford coefficients dispersion, suggesting improvements in formability and reducing the alloy’s planar anisotropy. These results revealed that annealing up to 400 °C or higher temperatures followed by water quenching leads to good strength and ductility ratios while reducing anisotropy.Peer ReviewedPostprint (published version

Mechanical and microstructural evolution of a 3D printed AlSi11Cu alloy

Additive manufacturing (AM) processes have attracted a great interest in the scientific community during the last five years. This paper presents the 3D printing of a hypoeutectic Al alloy obtained by the Selective Laser Melting (SLM) technique. The initially printed material presented a cellular Al matrix microstructure with interconnected Si networks. Different tensile behaviors were found depending on the orientation of the specimens for both the initial material and after the annealing heat treatment. The specimens cut in the printing direction recorded lower ductility values, while those from the perpendicular plane and in the radial direction showed higher ductility and strength values.Peer ReviewedPostprint (published version

Microstructure and Mechanical Properties of AA6082-T6 by ECAP Under Warm Processing

An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. Microstructural evolution of the alloy processed by ECAP with different passes were evaluated by using optical microscope, scanning electron microscopy coupled with an electron backscattered diffraction (EBSD) detector and X-ray diffraction. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished due to the presence of concurrent softening phenomena. Calorimetric analysis indicated a slightly increase in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with increasing ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes.Fil: Khelfa, T.. Northwestern Polytechnical University; China. University of Sfax; TúnezFil: Muñoz Bolaños, Jairo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Politécnica de Catalunya; EspañaFil: Li, F.. Northwestern Polytechnical University; ChinaFil: Cabrera -Marrero, J. M.. Universidad Politécnica de Catalunya; EspañaFil: Khitouni, M.. University of Sfax; Túne

Microstructure characterization of metallic materials processed by Equal Channel Angular Pressing (ECAP): an Electron Backscatter Diffraction (EBSD) analysis

This overview article discusses the Equal Channel Angular Pressing (ECAP) processing of different metallic materials. Particular emphasis is given to the microstructural evolution from the coarse grain (CG) to the ultrafine-grained (UFG) states throughout the electron backscattering diffraction (EBSD) technique. Iron-based alloys, such as duplex and 1020 low-carbon steels reached higher hardening with a lower deformation and lower non-ultrafine average grain sizes than the ultrafine pure iron condition due to fast grain fragmentation, i.e., more geometrically necessary dislocation (GND) grouping. Moreover, due to the magnesium adhesion, copper alloys reached superior mechanical properties compared to pure copper even when the initial grain size for as-cast alloys was over 1000 µm. On the other hand, low melting temperature (T MP) materials processed at 250°C, like the ZK60 magnesium and AA6082 aluminum alloys (i.e., homologous temperatures (TH) of 0.38T MP and 0.37T MP, respectively), showed grain refinement without reaching the ultrafine regime and mechanical softening due to the static and dynamic recrystallization phenomena. CP titanium also displayed heterogeneous grain sizes with average values of above 1 µm after four ECAP passes for temperatures ranging between 150°C and 400°C (TH between 0.09T MP ¹ 0.24TMP). The evolution of the GNDs suggested that the initial deformation stages of severe plastic deformation (SPD) by ECAP produced the most notorious density increments from 10 12 m¹2 to 1014 m¹2 , which level up at high deformations (more than four ECAP passes) around 1014 1015 m¹2 , explaining the fast and slow grain size reduction rates, respectively. The ECAP processing on different metallic material systems showed a larger grain fragmentation capacity in high melting points and alloyed materials, giving rise to steep yield strength increases and low ductility. The low ductility and grain size saturation correspond to a low capacity to create new grain boundaries manifested by the GNDs saturation in the UFG range.Peer ReviewedPostprint (published version