Pulse laser energy deposition of Inconel 625 alloy: Effects on microstructure and high-temperature oxidation resistance

Abstract

Despite the laser energy deposition technology has been applied in the field of surface modification and repair of Ni-based high-temperature alloys. However, the utilization of this technology to improve the high-temperature oxidation resistance of nickel-based alloys is still an important topic that needs to be solved urgently. In this study, a processing strategy involving modulation of the laser heat source output was adopted, utilizing five different pulsed laser waveforms—pulse, continuous, triangle, declining, and rising—to tailor the microstructure and elemental distribution of the coating, thereby enhancing the high-temperature oxidation performance of Inconel 625. Under all five waveforms, the coating phases showed no significant differences and consisted primarily of the γ phase with an FCC structure. In addition, waveforms with periodic oscillation characteristics (pulse and decline) effectively reduced pore volume and refined the microstructure. Among these, the pulse waveform yielded the lowest porosity of 0.131 %, compared to 1.176 % for the conventional continuous wave. Conversely, the triangle laser output form was smooth and produced a slow cooling rate that provided an optimal ratio of cooling gradient (G) to solidification rate (R) conducive to continuous growth of dendritic structures. The results of oxidation weight gain curve analysis showed that the pulsed-wave and falling-wave coatings had less mass gain after 100 h of oxidation at 900°C, demonstrating superior high-temperature oxidation resistance, which was mainly benefited from the cellular grain boundaries that provided more channels for the diffusion of elemental Cr after the grain refinement, and increased the concentration of elemental Cr at the edges. The reaction with O formed a denser Cr₂O₃ oxide layer, which inhibited the external diffusion of Ni ions and thus reduced the oxide defects. This study confirmed that modulating the laser output waveform was also an effective method to enhancing the high-temperature oxidation resistance of Ni-based alloys, which effectively saved the cost of the laser processing compared with methods such as adding mixed powders in the laser energy deposition process.