Process response of Inconel 718 to wire + arc additive manufacturing with cold metal transfer

• Published in: Materials & design 2020-10, Vol.195, p.109031, Article 109031
• Main Authors: Kindermann, Renan Medeiros, Roy, M.J., Morana, R., Prangnell, Philip B.
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Hardness; Heat treatment; Microstructure; Nickel alloys; Process stability
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2020.109031

Wire + arc additive manufacturing (WAAM) with cold metal transfer (CMT) process can reduce cost and lead time during the production of large-scale Ni-based components used in the transportation and energy sector. This paper investigates the effects of processing parameters and heat treatments employed on CMT-WAAM of a precipitation hardenable Ni-based alloy – Inconel 718. The process stability was analysed by electrical transients and melt pool imaging, showing an opposite trend to the measured heat inputs. A 1.2 mm diameter wire permitted deposition widths of 5.92–13.15 mm, but widths larger than ~10 mm decreased the arc stability considerably. Laves length and carbide diameter decreased with travel speed, while the as-deposited hardness increased. These observations permitted a linear wall to be fabricated with a minimal heat input per layer of 181–185 J/mm. An increase in the solution treatment temperature from 980 to 1040 °C reduced microsegregation, Laves and δ phase precipitation. Localised regions with high microhardness were found near interlayer regions due to a local dissolution of Nb-rich eutectic phases. Compared to powder-based additive manufacturing, CMT-WAAM IN718 exhibits a larger melt pool size and lower as-deposited hardness, but has been found to show satisfactory ageing response and similar Laves phase area fraction. [Display omitted] •Effects of processing parameters and heat treatments were investigated on Inconel 718 produced by wire + arc additive manufacturing.•Arc voltage signals and melt pool imaging were used to characterise the metal transfer and improve the process stability.•Average Laves length of 1.68–2.60 μm and NbC carbides diameter of 0.59–0.90 μm were measured by microstructural analysis.•Localised regions with high microhardness were found near interlayer regions after precipitation heat treatment.•An increase in the solution treatment temperature from 980 to 1040 °C reduced microsegregation, Laves and δ phase considerably.