A nickel based superalloy reinforced by both Ni3Al and Ni3V ordered-fcc precipitates

Abstract

A nickel based superalloy has been designed where the fcc γ Ni matrix is reinforced by two different ordered-fcc intermetallic compounds, γ L1 2 Ni 3 Al and γ D0 22 Ni 3 V. Primary ageing at 900 − 1000 • C precipitated spherical L1 2 Ni 3 Al, whose volume fraction and size were controlled by altering the ageing temperature and time. Secondary ageing at 700 • C for 1 − 1000 h precipitated D0 22 Ni 3 V laths. The duplex precipitation increased hardness by up to 85 HV, with ∼ 500 MPa compressive proof strength maintained at 800 • C. Electron microscopy studied the Ni 3 Al precipitation and confirmed the form of the secondary Ni 3 V precipitates and their long term stability.Nickel based superalloys are widely used due to their combination of strength, creep, toughness, environmental resistance and microstructural stability in the 650 − 1200 • C interval [1,2]. Such alloys exploit the two-phase field that exists within the Ni-Al binary system to produce microstructures comprising a γ face-centred cubic (fcc) A1 (Strukturbericht designation) matrix, Figure 1a, 5 reinforced with γ L1 2 Ni 3 Al ordered-fcc intermetallic precipitates, Figure 1b. A variety of additional phases are used in multicomponent (∼ 10) commercial superalloys, including other intermetallics as well as carbides and borides. However, there is an additional ordered-fcc D0 22 γ phase, Figure 1c, that can be exploited in superalloys, e.g. Inconel 718 [3], which is also being explored in 10 other alloy systems [4,5,6]. Unfortunately, the D0 22 Ni 3 Nb phase in Inconel 718 is metastable [7,8] decomposing into the δ Ni 3 Nb D0 a orthorhombic P mmn phase [9, 10]. The Ni 3 X type intermetallics adopt a number of stable crystal structures as the X element is changed due to differing formation energies. For Ni 3 X intermetallics with X = Nb, Ta, Mo the stable structure is D0 a , while for 15 X = Ti the D0 24 structure is adopted, and with X = Al and Si the traditional γ * Corresponding

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“…Figure 2 shows the temperature and stress distribution of the DZ125 blade in service are significantly geometry dependent, resulting in the fact that, as shown in Figure 4, the morphologies of the DZ125 blade after service may be quite diverse (Knowles et al, 2019). It should be noted that he evolution of γ′ precipitates is essentially the result of element diffusion which is related to temperature and stress.…”

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Perspective on intermetallics towards efficient electrocatalytic water-splitting

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