Fig.2. Schematic illustration of different positions of X90 bend.
To investigate the microstructure characterizes, small samples were cut
from the pipe part. Standard grinding and polishing technique were
employed to obtain mirror surface. Then, the polished surface was etched
with a solution of 4 vol.% natal to reveal the microstructure via Leica
DMIRM optical microscope (OM) and JSM-5900LV scanning electron
microscopy (SEM). Transmission electron microscopy (TEM) was carried out
to identify the phase composition, and examine the dislocation
distribution. The TEM foils were cut from the samples, mechanical
grinding to about 50 μm thickness. 3 mm disks were punched from the
foils and twin-jet electropolished with a solution of 75% methanol +
25% nitric acid as electrolyte at -30 ℃. Foils were examined with a
JEOL2010 TEM operated at 200 kV.
Electron back-scatter diffraction (EBSD) analysis was performed on a
FEI
NANO SEM 430 field-emission scanning electron micro-scope (FE-SEM) in
order to study the grain boundaries and local misorientation. Local
misorientation was used to evaluate small strain gradients in material.
The data were post-processed with Channel 5 software provided by Oxford
HKL Technology®. The specimens were electrolytically
polished a solution of 650 ml alcohol, 100 ml chlorate, and 50 ml
distilled water at room temperature for 20 s. The EBSD maps were
obtained using a step size of 0.15 μm, area over 60 μm × 60 μm.
Results and discussion