Cobalt-Base Superalloy Coating Using GTAW Process

Abstract

In harsh operational conditions, the low-alloy steels need to be protected from the environment. Thus, against corrosion and wear, an ordinary choice is metallic cladding. In this sense, the present study aimed to evaluate the properties of cobalt base superalloy coating deposited by gas tungsten welding process (GTAW) on steel SAE 4140. A circumferential weld was chosen due to its critical restraint. Four coating conditions were studied varying the welding currents. A microstructural evaluation was done using optical and scanning electron microscopy. The physical properties of coatings were additionally evaluated by microhardness measurement and dilution quantification. The results obtained indicated, for all conditions, a uniformity of layers. However, the deposited weld characteristics are strongly dependent on welding parameters. For the welding parameters studied, the maximum dilution of 60.8% was observed in coatings with austenitic and dendrite microstructures welded with 110 A current. Moreover, the metallographic analysis and microhardness tests showed, for some cases, the presence of partially diluted zone, a microstructural layer in the transition region of base metal and coating. The welding performed with current of 90 A showed the best combination of microhardness and dilution aspects, without defects in coating.