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SAE AS5491 Revision C, November 1, 2007
Calculation of Electron Vacancy Number in Superalloys
Description / Abstract:
Purpose
This SAE Aerospace Standard (AS) establishes a uniform procedure for calculation of electron vacancy numbers in superalloys. It is intended for use by suppliers of raw materials and parts, typically castings, for which control of electron vacancy number is required by the raw material specification.
Application
This procedure has been used to estimate the potential for alloy phase instability by calculation of the density of electrons per atom in nickel-based superalloys.
Background
Complex, highly alloyed superalloys have been observed, for some alloy chemistries and under certain conditions, to form precipitated phases which can adversely affect strength and ductility. These phases, typically of a crystalline structure known as topologically close-packed, or TCP, appear after extended exposure at temperatures in the range from 1300 to 1650 °F (704 to 899 °C). Such phases include sigma (σ), mu (μ), or Laves. Their tendency to precipitate from the alloy matrix has been related by researchers such as Boesch and Slaney (see 2.1) and Woodyatt, et al. (see 2.2) to the density of electrons per atom as expressed by the electron vacancy number Nv.
This SAE Aerospace Standard (AS) establishes a uniform procedure for calculation of electron vacancy numbers in superalloys. It is intended for use by suppliers of raw materials and parts, typically castings, for which control of electron vacancy number is required by the raw material specification.
Application
This procedure has been used to estimate the potential for alloy phase instability by calculation of the density of electrons per atom in nickel-based superalloys.
Background
Complex, highly alloyed superalloys have been observed, for some alloy chemistries and under certain conditions, to form precipitated phases which can adversely affect strength and ductility. These phases, typically of a crystalline structure known as topologically close-packed, or TCP, appear after extended exposure at temperatures in the range from 1300 to 1650 °F (704 to 899 °C). Such phases include sigma (σ), mu (μ), or Laves. Their tendency to precipitate from the alloy matrix has been related by researchers such as Boesch and Slaney (see 2.1) and Woodyatt, et al. (see 2.2) to the density of electrons per atom as expressed by the electron vacancy number Nv.
SAE AS5491 Revision C, November 1, 2007
Calculation of Electron Vacancy Number in Superalloys