E F was far smaller than one, suggesting its significant segregation behavior. For easy reference, all the k values were summarized in Table 5. The segregation behavior of several key elements in various nickel-based alloys has been reported in many published literatures (Refs. 28–32). DuPont et al. collected and summarized those equilibrium distribution WELDING RESEARCH coefficients in a table (Ref. 33), where one can find that the k values of Ni, Fe, and Cr are larger than one for many nickel-based alloys. The k value of Mo is in a range of 0.71–0.97, but that of Nb is in a range of 0.42–0.58. It is as expected that these metals in the deposited metals investigated in this study, shown in Fig. 8 and Table 5, behaved very similarly to those observed in other nickel-based alloys (Refs. 28–33). The interdendritic precipitates often exhibited in granular forms. Their sizes are mostly less than 1 m — Fig. 9A and B. The grain boundary phases frequently appeared with continuous or discontinuous fashion — Fig. 9A, C, and D. There is no suspense that those precipitates and grain boundary phases are carbides, oxides, and/or their mixtures. Their types could be roughly identified by the EDS analysis as listed in Table 6. The titanium oxides were found in both deposited metals — marked as 3, 4, 7, and 8 in Fig. 9 — while the aluminum oxide was found only in the deposited metal of the TiO2-SiO2-SrO type — marked as 8 in Fig. 9. The titanium and aluminum were introduced from the flux coatings (Table 1). A fact should be emphasized that all the particles investigated by EDS revealed very high niobium and carbon concentrations as shown in Table 6. It was reasonable to believe that they all included NbC. Previous research confirmed that (Nb, Ti) carbides and/or oxides independently nucleated and grew on the surface of the oxides (TiO2 and/or Al2O3) in different orientations, forming a complex compound in which the (Nb, Ti) carbides appeared as a rim around the core oxides (Refs. 34, 35). The grain boundary phases could be speculated to be Nb(Mo, Cr)C according to the EDS results (Table 6) — Fig. 9C—F. Mechanical Properties The tensile properties of the deposited metals of the two types of electrodes at room temperature did not exhibit a substantial difference — Fig. 10A. The two were above the minimum values listed in the standard AWS A5.11 ENiCrFe-9 (where the minimum tensile strength is 650 MPa, and the minimum elongation is 25%). DECEMBER 2016 / WELDING JOURNAL 475-s A C B D Fig. 9 — Intergranular and grain boundary precipitates along with the segregation phenomena across the grain boundary: A, C, and E — CaF2CaOSiO2 type; B, D, and F — TiO2CaF2SiO2 type. Table 5 — Chemical Compositions (wt%) and the Equilibrium Distribution Coefficients Element CaF2CaOSiO2 Type TiO2SiO2SrO Type Co Ccore k Co Ccore k Ni 68.78 69.98 1.02 68.91 70.17 1.02 Cr 14.77 15.64 1.06 14.91 15.97 1.07 Fe 6.60 6.92 1.05 6.44 6.83 1.06 Mo 4.11 3.33 0.81 4.27 3.27 0.78 Mn 3.62 3.22 0.89 3.53 3.01 0.85 Nb 2.12 0.91 0.43 2.04 0.75 0.37
Welding Journal | December 2016
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