PSI - Issue 60

Behrooz Tafazzolimoghaddam et al. / Procedia Structural Integrity 60 (2024) 575–581 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3. Results and discussion 3.1. Residual stress A map of residual stress in the direction perpendicular to the cut surface is shown in Figure 3. The data near the two pilot holes are distorted due to cutting induced artifacts and are discarded.

σ 33 (MPa)

Weld Stop

Y

X

Figure 3 Contour residual stress (MPa) perpendicular to the cut surface. The specimen was cut in the direction of the weld deposition

The contour stress map shows the highest tensile region at the centre of the cross section with leniency towards the weld stop. Although a more distinct high stress region was expected toward the last weld pass, the short travel distance for each weld bead and the slow cooldown of the previously deposited weld (since it is being reheated by the next weld pass) might have relaxed and re-distributed the stresses more evenly. The clad does not have high tensile stresses and in some areas has compressive stress which is favourable in terms of resistance to crack initiaion resulting from the missmatch is thermal expansion between austentitic stainless steel and Nickel. The process parameters such as powder feed rate, oscilation width, deposition speed, deposition geometry, and the energy input have direct infuence on the residual stress formation since they control the heat input and the melting / solidification. Characterizing these effecs are the next step in this ongoing study and a numerical simulatin of the deposition process is currenly underway. 3.2. Microstructure The microstructure of the weld cross section is shown in Figure 4. The weld passes are clearly visible and marked. Figure 4a & b show high resolution images of the weld and substrate interface with grain boundaries in the substrate made visible in Figure 4a and the dendritic region of the deposited 75Ni13.5Cr2.7B-3.5 Si is visible in Figure 4b. The interface is visible as a band with approximately 10 µ m width typical for dissimlar material deposition. The boundary between the two regions does not have a smooth transition and are separated by a distinct feature visible as a dark line in Figure 4a.

b

a

Figure 4 The micrographs of the deposited Colmonoy on steel substrate. a) weld zoom-in with visible grains in the substrate b) weld zoom-in adjusted for the dendritic phase visibility