In-situ dual wire arc additive manufacturing of NiTi-coating on Ti6Al4V alloys: Microstructure characterization and mechanical properties

In this study, the wire arc additive manufacturing (WAAM) technique was utilized to deposit a protective NiTi layer on a Ti6Al4V substrate through in-situ alloying of separate pure Ni and Ti wires to enhance the surface mechanical properties. The influence of arc current on the microstructure, phase formation, microhardness transition and dry-wear characteristics of the coatings were systematically analyzed. Crack-free and dense composite coatings, consisting of major NiTi2 phase with minor coarse NiTi dendrites or with fine α Ti dendrites, depending on the arc current, were obtained. The maximum average microhardness value of 818 HV0.2 was achieved with applied current of 60 A, which is 2.4 times more than that of the uncovered substrate. Sliding wear results revealed that the NiTi coatings exhibited superior wear resistance to the substrate and the coefficient of friction was considerably lower than that of the uncoated substrate. The best wear resistance, according to the lowest wear rate and friction coefficient, was obtained by the coating processed with 60 A. This study proves that the application of in-situ dual wire arc additive manufacturing of surface coatings for improved wear-resistant properties is feasible and promising in terms of time and cost savings.