African Fusion June 2017

Welding process % Fe in Layer 1 % Fe in Layer 2 Deposition rate kg/h] GMAW Pulse 18.48 3.40 3.17 CMT 2.38 0.37 4.61 Time Twin 15.69 3.60 10.73 CMT Twin 2.78 0.31 7.50 GTAW Cold wire 12.74 2.26 0.75 GTAW Hotwire 7.37 1.34 1.62 Laser Cladding 16.37 3.96 5.19 Table 2: Fe content in layers 1 and 2.

Figure 2: A welding process diagram for TIG hot wire welding.

Figure 1: The surface of an Inconel 625-clad layer after a high-temperature corrosion test [3]: a) Fe content of 2,5%: b) Fe content of 10%.

deposition rate. The comparison shows that a process that provides a low heat input and therefore a lowFe percentage cannot achieve high deposition rates. On the other hand, high deposition pro- cesses produce the highest percentages of Fe content. GMAW with hot wire The use of the GMAW pulsed welding for cladding was presented in Table 2. The main disadvantage of the process is a high % Fe content in the clad layer. Combined with the limited maximum arc power and associated limited pro- ductivity in terms of deposition rate, GMAWpulsedwelding is applicable only in a few cases. The addition of filler material from outside the GMAW process could offer a significant improvement inproductivity. In addition, the deposition of more filler material with a proportionally small increase in the welding power would have a positive effect on the dilution and, therefore, on the Fe content in the clad layers. The process setup is shown in Figures 4 and 5. The possible deposi- tion rates are comparable with most twin wire GMAW processes. Application The application of the GMAW hot wire process is easy to setup, adjust and maintain. Highest travel speeds and highest deposition rates can be reached when the process is applied with the help of mechanised manipulators. The welding system is put together

pends on two factors: hot wire current, which is adjusted in the hot wire power source; and the electrical resistance of the filler material itself. The positive ef- fect of the preheating compared to cold wire welding is shown in Figure 3. This effect can be also applied to welding processes other than TIG. Other cladding process variants In [5], claddingwith Inconel 625 for vari- ous welding processes is investigated. Measurements of the iron content in the clad layers were taken with EDX line scans. Energy-dispersive X-ray spectros- copy (EDS, EDX, or XEDS) – sometimes called energy dispersive X-ray analysis (EDXA) or energy dispersive X-ray mi- croanalysis (EDXMA) – is an analytical technique used for element analysis or characterisation of a sample. It relies on an interaction of some source of X-ray excitation and a sample. The iron content was measured in steps of 0.5mmstarting fromthe surface of theweld overlay to the basematerial. As a reference value for the dilution of the basemetal, the Fe content was used. Welding processes with high energy density or ones with low welding speed (GTAWwith coldwire and laser cladding) exceed the dilution rate of 5.0% iron con- tent, whilewelding processeswith lower heat input were shown to maintain the Fe content below 5.0%. All samples have in common a steep rise of the iron content when approach- ing the basematerial. Table 2 shows the iron content for the two layers, and the

Figure 3: Deposition rates of cold wire and hot wire welding as a function of arc energy [4].

Figure 4: A process diagram for GMAW hot wire welding.

using standard components: GMAW welding system Phoenix 551 Progress Puls (Figure 6); and an additional wire feed systemwith an integratedTigspeed drive 45 hotwire power source (Figure 7). Figure 5: A photograph of the GMAW arc and the hot wire entering the weld pool.

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June 2017

AFRICAN FUSION