PSI - Issue 43

Orsolya Molnárová et al. / Procedia Structural Integrity 43 (2023) 166–171 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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al. (2011, 2012) passed the sample through a channel containing two or three shear zones. A very recent technique called high‐pressure tube shearing (HPTS) was developed by Lapovok et al. (2017). In HPTS, the tube wall is thinned by the pass through the form and simultaneously sheared by rotating outer and inner parts of the form. As a result, a gradient ultra-fine-grained microstructure occurs in the final tube. All the above-mentioned ways result in the formation of ultra-fine-grained tubes, however, the starting form of the material is also a tube. In contrast, we focused on the production of the tube from a rod sample and developed the complex shearing of extruded tube (CSET) technique (Molnárová et al. 2020, 2021, 2022). This method is based on extrusion to produce a tube followed by two consecutive ECAP-like passes. Simultaneously, the mandrel rotates thus introducing further twist deformation of the inner wall surface of the tube. In summary, the application of CSET results in one-step production of a tube with an ultra‐fine‐grained and frequently gradient microstructure. As a result, the strength of the product of the 3003 aluminum alloy is extensively enhanced (Molnárová et al. 2020, 2021, 2022). In this contribution, we describe a detailed investigation of the microstructural changes occurring in the sample of an aluminum single crystal in the deformation zone during CSET. 2. Experimental Aluminum (99.5%) single crystal of a diameter of 22 mm and length of 100 mm was grown by seedless Bridgman method in a Granat furnace using graphite crucible having a conus in the bottom part, under argon atmosphere. The growth velocity was 11 mm h – 1 and the crucible rotated at 5 rpm. The billet with a length of 55 mm and a diameter of 10.9 mm with  148  axis orientation (as proven by the X-ray Laue backscattering method) was prepared from the annealed ingot by electro-spark cutting. CSET process was performed at room temperature. The CSET process is schematically shown in Fig. 1a. The plunger was pressing the sample with a velocity of 0.2 mm s – 1 . Simultaneously, the mandrel rotated with a frequency of 12 rpm. The CSET processing resulted in a tube with a wall thickness of 2 mm and an outer diameter of 26 mm. All manufacturing details are described by Molnárová et al. 2020 .

(a) (b) Fig. 1. (a) Principle of the CSET process; (b) detail of the sample with marked points of analysis.

Scanning electron microscopy (SEM; FEI Quanta 3D FEG) was used for the investigation of the microstructure of the CSET processed tube. Besides this observation, electron backscatter diffraction (EBSD) measurements were performed in SEM on samples, which were electrolytically polished at – 20 °C for 120 s with a voltage of 10 V in a 10% solution of HClO 4 in ethanol. The EBSD step size was 50 nm (2  m in the case of the map shown in Fig. 3a). The grain size and orientation were evaluated. Besides, the lattice distortion of the grains was determined using Kernel average misorientation (KAM) maps.