TEM analysis of Cr–Mo–W–B phase in a DS nickel based superalloy

Excerpt

Rene 80 is a precipitation hardened nickel-based superalloy, which is widely used to manufacture components of gas turbine engines for aerospace and power generation applications. It is designed to withstand service temperatures of up to 980 °C [1] and possesses remarkable hot corrosion resistance, long-term microstructural stability, and high-temperature strength produced primarily by precipitation hardening by ordered intermetallic Ni₃(Al,Ti) γ′ precipitates. Directional solidification (DS) processing of the alloy results in further improvement of its elevated temperature properties and permits the use of a higher service temperature, which improves the thermal efficiency of gas turbines [2‐5]. It has been reported that in DS Rene 80, the tensile strength is increased by about 10–15% and the creep rupture life is extended by 2–4 times relative to conventionally cast material [5]. Boron is an essential minor elemental addition to these heat resistant materials primarily to improve their creep rupture properties [3, 4]. Nevertheless, it has been recognized that the mode in which boron exists on grain boundary regions, either in austenitic solid solution form or selectively partitioned into second phase particles, can significantly influence the creep properties of superalloys [6, 7]. Experimental study is crucial in establishing the presence and nature of intergranular borides in multi-component superalloys due to the influence of interfacial elemental segregation that is not generally considered during thermodynamic equilibrium calculations of theoretical models [8]. The objective of this investigation was to perform transmission electron microscopy (TEM) study of heat-treated DS Rene 80 superalloy to understand the nature of boron rich second phase particles present along its grain boundary regions. …