RESUMEN
The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m-2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m-2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD.
RESUMEN
The microstructure and texture of the intermetallics in Al/Mg/Al multi-layer composite fabricated by Accumulative Roll Bonding (ARB) at 400 °C up to 6 cycles were investigated using Electron BackScatter Diffraction (EBSD) and Synchrotron X-ray Diffraction (SXRD). EBSD and SXRD analysis have shown that ARB processing leads to the formation of Al3Mg2 and Mg17Al12 intermetallics soon after the second ARB cycle with a global thickness of 12 (N = 2) to 22 µm (N = 6). The polycrystalline intermetallics plates growth was columnar and normal to the bonding interface. A constitutional liquefaction region was depicted ahead of the plates with an unusual rugged migration front. The Al3Mg2 and Mg17Al12 intermetallic compounds which formed after 2 ARB cycles have approximately the same average grain size (1.0 µm) at this cycle. After 4 ARB cycles, the grain refinement of Al3Mg2 is more than 4 times higher than in Mg17Al12. The average grain size of Al3Mg2 and Mg17Al12 reach 0.2 and 0.9 µm, respectively. After 6 cycles of ARB, the average grain size of both Al3Mg2 and Mg17Al12 increased to 1.5 µm and 2.8 µm, respectively. The dislocation density obeyed a ρAl3Mg2 > ρAZ31 > ρAl 1050 â¼ ρMg17Al12 hierarchy after N = 4 and 6 ARB cycles and the Al3Mg2 was shown to store more dislocations. Through the ARB processing, a usual strong basal (0002) texture was depicted in AZ31 layers and a weak rolling texture was shown in Al 1050 layers with a dominant Rotated Cube (001) 110 > component that vanished after upon increasing ARB cycles. The Al3Mg2 and Mg17Al12 intermetallics were characterized by a random texture.
RESUMEN
In this paper, the traceability of copper from the anode to the cathode and then the wire rod has been studied in terms of impurity content, microstructure, texture, recrystallization kinetics, and ductility. These characterizations were obtained based on secondary ion mass spectrometry, differential scanning calorimetry (DSC), X-ray diffraction, HV hardness, and electron backscattered diffraction. It is shown that the recrystallization was delayed by the total amount of impurities. From tensile tests performed on cold drawn and subsequently annealed wires for a given time, a simplified model has been developed to link tensile elongation to the chemical composition. This model allowed quantification of the contribution of some additional elements, present in small quantity, on the recrystallization kinetics. The proposed model adjusted for the cold-drawn wires was also validated on both the cathode and wire rod used for the study of traceability.
RESUMEN
The microstructural evolution of a cold drawn copper wire (reduction area of 38%) during primary recrystallization and grain growth was observed in situ by electron backscatter diffraction. Two thermal treatments were performed, and successive scans were acquired on samples undergoing heating from ambient temperature to a steady state of 200°C or 215°C. During a third in situ annealing, the temperature was continuously increased up to 600°C. Nuclei were observed to grow at the expense of the deformed microstructure. This growth was enhanced by the high stored energy difference between the nuclei and their neighbors (driving energy in recrystallization) and by the presence of high-angle grain boundaries of high mobility. In the early stages of growth, the nuclei twin and the newly created orientations continue to grow to the detriment of the strained copper. At high temperatures, the disappearance of some twins was evidenced by the migration of the incoherent twin boundaries. Thermal grooving of grain boundaries is observed at these high temperatures and affects the high mobile boundaries but tends to preserve the twin boundaries of lower energy. Thus, grooving may contribute to the twin vanishing.