PSI - Issue 43

Zuzana Molčanová et al. / Procedia Structural Integrity 43 (2023) 89– 94 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

91

3

2.2. Microscopic observations Microstructure of the as-prepared sample and after OC1 and OC2 heat treatments were observed by electron microscopy. Because the chemical etching method preferably reveals microstructure of only one of the welded materials, a low-energy Ar+ ion etching was used (Hitachi IM 4000 milling system), which in the end visualizes the microstructure of the two materials. The observation of the ion etched surfaces was performed on scanning electron microscope Hitachi SU 70 operated with electron accelerating voltage of 30 kV. 2.3. Micro X-ray diffraction To determine phase composition and residual stresses of the interface and in surrounding regions, a hard X-ray micro-diffraction experiment was performed at the beamline P07 at the PETRA III, DESY Hamburg Schell et al. (2014). During the experiment, monochromatic synchrotron radiation of photon energy 78 keV (λ = 0.015895 nm) was used. The beam of photons was focused down to the size 2 μm (vertically) x 30 μm (horizontally) and then collimated on the sample. The measurement tilt and rotation angles φ and ψ were fixed to 0º, see figure 1 , while the materials were scanned shot-by-shot equidistantly along a straight path (the yellow line on the sample shown in Fig. 1 left). The interface of the as-prepared material was measured by fine step 1 μm , and the annealed materials were scanned to a larger extent but with a coarser 250 μm step. During each step, the sample was illuminated by highly intense hard X-rays for 8 seconds. The resulting 2D XRD patterns were recorded using the Perkin Elmer 1621 detector. The recorded XRD patterns were radially integrated to I(2θ) space using the Fit2D software Hammersley & IUCr (2016). Internal strain/stress were determined directly from the 2D patterns applying the XRD 2 theory, (He, 2018), implemented in the GSAS II crystallography data analysis software Toby & von Dreele (2013). Later, for the stress calculation, we used material constants listed in Table 1. Table 1. Parameters for X-ray stress determination: distances between crystallographic planes of stress-free samples d 0 , Elastic modulus E, Poisson’s ratio  , and the anisotropic factor A RX Material, Phase, crystallographic planes d 0 [nm] E [MPa]  A RX

Alloy 625, bcc, (222)

0.1019

199 500

0.312

1.52

Ferritic steel P355NH, ferrite, (220)

0.1013

210 000

0.28

1.49

Fig. 1. Orientation of diffraction and sample coordinate systems.