Microstructural and mechanical characterization of as-cast nickel-based superalloy (IN-713C)
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pyright 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00540-0
Abstract Inconel 713C as-cast test pieces were produced by investment casting. The tensile properties at 25 and 650 C were obtained along with microstructural and microfractographic characterization. The tensile testing results followed the requirements of the AMS 5391D standard. Additionally, stress-rupture testing at 982 C and 152 MPa, and 815 C and 305 MPa was carried. The aged c - c0 microstructures were compared and discussed in
terms of rafting kinetics. The stress-rupture results followed the AMS 5391D requirements. The relationship between the as-cast and aged microstructures and the mechanical properties was discussed.
Introduction
quality and dimensional precision.1–3,6,7 IN-713C cast alloy is popular due to its appropriate castability, good tensile properties and maximum service temperature around 980 C, allied to suitable oxidation and thermal fatigue resistance.4–19 The mechanical properties are mainly controlled by the c - c0 duplex microstructure, and improved stress-rupture life can be obtained by solution heat treatment.4,20–27
Nickel-based superalloys are used at elevated temperatures due to their excellent mechanical properties and oxidation resistance.1–3 Wrought nickel-based superalloys feature superior tensile strength (up to 1600 MPa for Rene 95) and ductility (up to 55%, IN 617) when compared to cast nickel-based superalloys (tensile strength up to 1200 MPa for MAR M432, and ductility up to 14%, for IN-713LC). The microstructure of cast Ni-based superalloys combines the c matrix with a proportion of coherent c0 (Ni3Al) submicron precipitates along with primary carbides and borides.1–3 Inconel 713C (IN-713C) was the first of several cast nickel–chromium-based superalloys developed by the International Nickel Company during the 1940s.4,5 In this sense, some parts of the aircraft turbine present a complex geometry, which does not allow the intensive use of machining processes, favoring the investment casting process. This process’s low cooling rate is suitable for the production of parts with large grain sizes, excellent surface
Received: 28 August 2020 / Accepted: 15 October 2020
International Journal of Metalcasting
Keywords: IN-713C Ni superalloy, Mechanical testing, Microstructure, Thermal exposure, Rafting
Thermodynamic equilibrium calculation (see Figure 1a) shows a solidification sequence of IN-713C alloy taking place in a 75 C interval: L ? L ? c ? L ? c ? MC ? L ? c ? MC ? M3B2. Few studies using thermal analysis reported the formation of the MC carbide (M = Nb, Mo, Zr and Ti, FCC structure) before the c dendrites.13 The thermodynamic modeling of IN-713LC using a Scheil–Gulliver solidification simulation is shown in Figure 1b. This simulation indicated a different solidification sequence taking place in a broader interval (* 200 C): L ? L ? c ? L ? c ? MC ? L ? c ? MC ? M3B2 ? L ? MC ? M3B2 ? c ? c0 . In these conditions, the segregation of C, Mo, Zr, Cr, Nb, B, Al and Ti to the interdendrit
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