In the search for versatile and effective weld cladding processes to deposit ultra-wear-resistant Ni-WC MMC (Ni-based tungsten carbide metal matrix composite) overlays for mining applications, there is an increasing interest in exploring advanced low-heat-input cold metal transfer (CMT) method. Depositions of single weld bead tracks of Ni-WC MMCs on steel plates were performed by employing the CMT process; Taguchi's design of experiments was used to plan the experimental investigation. All weld tracks exhibit continuous and uniform bead profile and sound metallurgical bonding to the substrate. Retained WCs are present in the overlay tracks relatively uniformly. The formation of primary WC and secondary carbides is observed depending on the level of dilution. In contrast to standard gas metal arc welding processes, the volume fraction of retained WC, which is negatively correlated with dilution level, is not directly interrelated with heat input for the CMT process and can reach a high level together with improved weld bead appearance at high deposition rate. Deposition rate has a positive correlation with average instantaneous power, which is, in turn, positively correlated with wire feed speed. The addition of oxygen into shielding gas mixtures promotes carbide transfer from cored feed wire to the weld track and increases the volume fraction of retained WC. Analysis of signal-to-noise ratios shows that it is difficult to find a single set of optimized processing parameters, and trade-offs are needed in engineering practice. The present investigation demonstrates that the Taguchi method is a powerful tool in process improvement for weld cladding of Ni-WC MMC overlays.
Keywords: Carbide dissolution; Carbide transfer efficiency; Cold metal transfer (CMT); Retained WC; Taguchi design of experiments; Weld cladding.
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