2.2. Microstructural analysis
The morphologies of grains and precipitates in BM, HAZ and WNZ were
investigated. Optical microscopy
(OM) observation was performed using Leica DFC 295 in polar light mode.
Electron backscatter diffraction (EBSD) analyses were performed using
ZEISS Sigma 300 field emission gun
scanning electron microscope with a scanning step size of 0.15 μm. The
EBSD data was analyzed by Channel 5 software to acquire microstructure
statistics information. Boundaries with misorientations less than 15°
were defined as low-angle grain boundary (LAGB) and those with
misorientations greater than 15° were defined as high-angle grain
boundary (HAGB), respectively. The scanning electron microscopy (SEM)
observation of fracture surface were also operated by ZEISS Sigma 300 at
20 KV. Transmission electron microscopy (TEM) and high resolution
transmission electron microscope (HRTEM) observations were carried out
on FEI Tecnai G2 F20.