Hot Corrosion and Mechanical Performance of Repaired Inconel 718 Components via Laser Additive Manufacturing

Abstract

Hot corrosion is one of the crucial failure modes of Ni-based superalloy components operating at high temperatures, which inevitably affects the subsequent mechanical properties of the alloys. In this research, damaged Inconel 718 alloy components with a pre-made trapezoid groove are repaired using laser additive manufacturing technique, and the change mechanisms of the microstructure and tensile properties of the repaired Inconel 718 alloy due to the hot corrosion in the salt mixture of 87.5 wt.% Na2SO4 + 5 wt.% NaCl + 7.5 wt.% NaNO3 at 650 °C for different durations are investigated. The results show that oxidation and Cr-depletion occur on the repaired components due to the hot corrosion, and the corrosion products are mainly composed of Cr2O3, Fe3O4, and Ni3S2. The tensile strength and elongation of the as-repaired specimens are 736.6 MPa and 12.5%, respectively. After being hot corroded for 50 h, the tensile strength increases to 1022.9 MPa and elongation decreases to 1.7%. However, after being hot corroded for 150 h, both tensile strength and elongation of the repaired specimens drop to 955.8 MPa and 1.2%, respectively. The mechanical performance alteration is highly related to thermal effects instead of the molten salt attack.

Laser Remelting Process Simulation and Optimization for Additive Manufacturing of Nickel-Based Super Alloys

“…Figure 16 c,d shows the cross sections of grooves filled by DMD without and with prior laser remelting. Similar to the findings of Zhang et al [ 25 ], there is a high bonding quality for both conditions, without bonding defects. The specimen with prior laser remelting shows a more regular bonding depth, especially in the inclined wall area.…”

Suitability of Laser Engineered Net Shaping Technology for Inconel 625 Based Parts Repair Process

“…It was found, that the LENS could be successfully applied for the repair process and prevent effectively the phase transformations on the border of the cladding and substrate material resulting from the extremely high temperature. Zhang et al [ 27 ] performed the repair of the Inconel 718 components by means of laser additive manufacturing. In this study, the Inconel 718 was deposited on the substrate of the same material with a trapezoid grove by a fiber-coupled diode laser system (Laserline LDF400–2000, Mülheim-Kärlich, Germany) which was characterized by the wavelength of 980 nm and maximum laser power of 2 kW.…”

“…Additionally, the molybdenum addition transforms the Laves phase morphology and decreases the segregation zone around the Laves phase. Moreover, the research of Zhang et al [ 27 ] presents, that the laser repair technology applied for the Inconel 718 alloy components led to elemental precipitation and the occurrence of the Laves phase. It could be concluded, that the process parameters proposed by the authors in a recent study enable a slight reduction of a phase transformation that occurred due to the high temperature resulting from the relatively high laser power of 900 W.…”

Laser direct energy deposition – the effect of process parameters on inconel 718

“…As previously stated, this phase is detrimental to Inconel 718 mechanical properties as it reduces strengthening phases such as γ" from being formed (Witzel, Stannard, Gasser, & Kelbassa, 2011;Zhang Q. , Zhang, Zhuang, Lu, & Yao, 2020). As Laves formation is promoted by increased Nb and Mo segregation, this can be reduced by using a dwell time between depositing adjacent tracks and subsequent layers.…”

“…To mitigate elemental segregation, and subsequent formation of Laves, it is suggested that process conditions such as heat input, cooling rate and thermal gradients should be controlled (Radhakrishna & Prasad Rao, 1997) The dominant microstructure obtained for DED-L Inconel 718 consists of columnar dendrites elongated in the direction towards the heat sourceessentially consisting of γ-dendrites and interdendritic Laves (Jelvani, Razavi, Barekat, Dehnavi, & Erfanmanesh, 2019;Smith, et al, 2016;Zhao, Chen, Lin, & Huang, 2008;Zhang Q. , Zhang, Zhuang, Lu, & Yao, 2020;Mantri, et al, 2021). Laves forms irregularly, with morphology differing between laser powers (Zhu, Xu, & Gu, 2018).…”