Transformation of the nickel aluminide alloy structure through the application of a heat-resistant coating using oscillation electrode surfacing

Abstract

This study considers the formation of an alloyed nickel aluminide structure through automatic electric arc surfacing employing an oscillating electrode composed of composite wire. The arc transversely traverses the weld pool surface at a frequency denoted as f. In comparison to conventional surfacing techniques, this process either displaces the crystallization front alongside the weld pool (at f  = 1.3 Hz) or stabilizes it (at f  ≥ 2 Hz) throughout the cross-sectional area of the coating layer. We have conducted an investigation into the evolution of alloy structures resulting from surfacing. Notably, we have observed that the regions with concentrations of eutectic nickel-aluminum are particularly susceptible to structural alterations. The formation of particle clusters, which is contingent upon heat dissipation conditions near the crystallization front, leads to the development of layered texture regions. Our findings reveal that following 50 thermal cycles (heating to 1100 °C, cooling to 25 °C), the alloy's hardness becomes independent of subsequent thermal cycles, consistently maintaining a level 34–35 HRC. The highest resistance of the surfaced metal to thermal fatigue cracks is achieved when its structure exhibits an optimal  γ-solid solution (relatively ductile) to nickel-aluminum cooling martensite ratio, corresponding to the Ni2Al phase. The thermal conditions necessary for producing such a structure are elucidated by the gradual cooling of the crystallized metal from elevated temperatures when f  ≥ 2.8 Hz. An analysis of changes in oxidative wear, estimated by mass loss, during thermal fatigue tests conducted at a metal heating temperature of 1100 °C revealed the superiority of the studied alloy over industrial alloys based on nickel and cobalt.