High-temperature failure and microstructural investigation of wire-arc additive manufactured Rene 41

Abstract

In developing a wire-arc plasma direct energy deposition process for creep-resistant alloys used in high-speed flight applications, structures were built from nickel-based superalloy Rene 41. Samples of additive manufacturing (AM) material were analysed for their microstructural and mechanical properties, in both as-deposited (AD) and heat-treated (HT) conditions. Tensile specimens were tested at room temperature, 538, 760, and 1000 °C. Macroscopically, large columnar grains made up of a typical dendritic structure were observed. Microscopically, significant segregation of heavier elements, grain boundary precipitates, and secondary phases were observed, with key differences observed in HT material. There was a clear distinction between failure modes at different testing temperatures and between AD and HT variants. A fractographic investigation found a progressive move from brittle to ductile fracture with increasing testing temperature in both AD and HT conditions, as well as microstructural features which support this observation.

A performance comparison of additive manufactured creep-resistant superalloys

“…Which separates them from potential Laves phases in area A which is Mo rich. Similar features were also observed by James et al in RE41 [13].…”

“…Similar grain boundary locations in both the as deposited and heat-treated conditions are presented in Figure S-4. The observed structures are similar in appearance with a directionally solidified grain structured consisting of long dendrites extending through the height of the samples in the BD axis, which was also observed by James et al [13]. A thicker dendritic structure and grain boundaries are seen in heat-treated samples.…”

“…The best overall performance, as anticipated from the literature, is RE41 followed by IN718 and H188. In RE41 and also in IN718, as-deposited performance was seen to increase at the 760°C test compared to the 538°C performance, the same phenomenon was previously seen by James et al in RE41 [13]. The worse performing alloy compared with maximum stated values from literature is as-dep IN718 which achieved on average 47.8% of the maximum values, followed by RE41 58.8% and the closest performance H188 achieving 63.7% of the stated maximum.…”

“…Following this the suitability of these WAAM built alloys for high-speed flight was discussed. The study shown here is a continuation on the previous work of James et al into the room-temperature properties of the same alloys [11][12][13].…”

“…δ phases are not seen generally due to Cr and Mo being tied up in the carbides. Laves phase can form where C is less than 0.05% and Al less than 1% at 815°C [13,22]. The main carbides are M 6 C (Mo,Co) 6 C and/or M 23 C 6 (Cr 23 C 6 ), which form at higher temperatures due to higher Mo and W content [23][24][25].…”