Fig. 14 — Composition measurements of a big tungsten carbide particle in cladding No. 9 (Fig. 11) showing W3C2 as well as the previously reported WC and W2C inside partially melted tungsten carbide particles. Points of measurements are superimposed on an SEM image for better contrast between phases. other elements in Table 5, the total contents of all the elements in the weld-pool liquid is now 95.675 wt-% (= 37.88 wt-% W + 0.33 wt-% Si + 0.64 wt-% B + 55.45 wt-% Ni + 1.035 wt-% C + 0.34 wt-% Fe). Since the total should be 100%, each alloying content should be multiplied by a factor of 1.045 (= 100 / 95.675). Thus, the composition of the liquid in the weld pool is as follows: 39.58 wt-% W, 0.34 wt-% Si, 0.67 wt-% B, 57.95 wt-% Ni, 1.08 wt-% C, and 0.36 wt-% Fe or just Ni- 39.58W-1.08C-0.67B-0.36Fe-0.34Si by wt-%. Figure 20A shows the solidification path of the liquid metal in the weld pool based on the composition of Ni- 39.58W-1.08C-0.67B-0.36Fe-0.34Si. The solidification path is the curve of temperature T vs. fraction of total solid fS during solidification. The curve was calculated using thermodynamic software Pandat (Ref. 24) and Ni-alloy database PanNickel (Ref. 25) of CompuTherm, LLC. The arrowheads indicate the points at which solid phases start to form from the liquid during cooling. A B As shown, before -Ni starts to form at about 1380°C, WC forms from the liquid at about 1650°C. This WC formation probably occurs on the unmelted portions of the tungsten carbide particles, that is, by epitaxial growth as “halos” around the unmelted portions of the particles. Epitaxial growth is much easier since WC does not have to nucleate from the melt. Figure 20A shows -Ni starts to form just below 1400°C. So, in Fig. 20B the big hump in the WC curve just below 1400°C indicates WC forming while -Ni dendrites grow, and this WC is likely to exist in the interdendritic areas. At about 1300°C M2B boride begins to form, where M contains Ni, Fe and W. At about 1060°C, Ni3B boride begins to form in the form of eutectic Ni-Ni3B. Figure 20B shows the fractions of solid phases during solidification. The Ni-rich phase -Ni, which has a much higher fraction than all other solid phases, is not included in order to show other solid phases WELDING RESEARCH 462-s WELDING JOURNAL / DECEMBER 2016, VOL. 95 Fig. 15 — Composition measurements in interdendritic area in cladding No. 9 (Fig. 11).
Welding Journal | December 2016
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