SAE AS 5491C-2007 Calculation of Electron Vacancy Number in Superalloys《超耐热合金中电子空位的计算》.pdf

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5、3-10 Superseding AS5491B Calculation of Electron Vacancy Number in Superalloys RATIONALE AS5491C has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE 1.1 Purpose This SAE Aerospace Standard (AS) establishes a uniform procedure for calculation of electron vacancy numbers in su

6、peralloys. 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. 1.2 Application This procedure has been used to estimate the potential for alloy phase instability by calculation

7、 of the density of electrons per atom in nickel-based superalloys. 1.3 Background 1.3.1 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, typica

8、lly 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 (), mu (), or Laves. Their tendency to precipitate from the alloy matrix has been related by researche

9、rs 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, as shown in Equation 1, as follows: g166=n1iiviv)N(mN (Eq. 1) where: Nvis the electron vacancy number for the alloy miis the atomic mass fraction

10、 of the ith element in the alloy composition, and (Nv)iis the electron vacancy number of the ith element. Determination of the electron vacancy concentration requires an understanding of the phases which precipitate in superalloys as well as the sequence in which they form in the gamma matrix. In ge

11、neral, this sequence is (a) the precipitation of borides, (b) the precipitation of carbides, and (c) the formation of gamma prime. When these phase reactions are considered, and adjustments made to the composition to take them into account, the residual matrix composition may be determined. From tha

12、t residual matrix the electron vacancy number is then calculated. 1.3.2 The sequence of precipitation of strengthening phases is addressed as follows: 1.3.2.1 Nickel, chromium, titanium, and molybdenum form a boride as (Mo0.5, Ti0.15, Cr0.25, Ni0.10)3B2. 1.3.2.2 All carbon is assumed to form carbide

13、s of the type MC and M23C6. It is assumed that MC carbides take half the carbon, reacting in sequence with tantalum, columbium, zirconium, titanium, and vanadium. The remaining carbon then reacts with chromium, molybdenum, and tungsten to form Cr21(Mo,W)2C6. 1.3.2.3 Gamma prime is formed from the re

14、maining aluminum, titanium, hafnium, columbium, tantalum, 50 percent of the original amount of vanadium, and 3 percent of the original amount of chromium by combining with three times that total in nickel, i.e., Ni3(Al, Ti, Cb, Hf, Ta, 0.5V, 0.03Cr). 1.3.2.4 The remaining chromium content is adjuste

15、d for that lost due to formation of borides, carbides, and gamma prime. 1.3.2.5 The remaining nickel content is adjusted for that tied up in boride and gamma prime formation. 2. REFERENCES 2.1 W. J. Boesch and J. S. Slaney: Metal Progress, July 1964, Vol. 86, No. 1, pp 109-111. 2.2 L. R. Woodyatt, C

16、. T. Sims and H. J. Beattie, Jr.: Transactions of the Metallurgical Society of AIME, April, 1966, Volume 236, pp 519-527. 3. TECHNICAL REQUIREMENTS 3.1 Calculation of Nv3.1.1 Nvshall be calculated in the following order: 3.1.1.1 Conversion of weight percentage to atomic percentage for each element 3

17、.1.1.2 Calculation of boron and carbide precipitation 3.1.1.3 Calculation of gamma prime precipitation 3.1.1.4 Calculation of the residual gamma matrix composition 3.1.1.5 Determination of electron vacancy number, Nv3.1.2 It may be helpful to set up a matrix similar to Table 1 to facilitate recordin

18、g compositions through the process of electron vacancy number calculation. SAE INTERNATIONAL AS5491C Page 2 of 7_ TABLE 1 - MATRIX FOR CALCULATION OF Nv(ELECTRON VACANCY NUMBER) SAE INTERNATIONAL AS5491C Page 3 of 7_ TABLE 1 (CONTINUED) Sample Calculation based on AMS 5410: Matrix for Calculation of

19、 Nv(Electron Vacancy Number) SAE INTERNATIONAL AS5491C Page 4 of 7_ 3.2 Conversion to Atomic Fraction 3.2.1 Enter in column A the weight percent of the individual elements by row. When the weight percent is unknown, or the element is not found in the alloy, enter zero (0). The weight percent of nick

20、el is determined by adding the percentages of the other elements and subtracting the sum from 100. 3.2.2 Divide the weight percent of each element (the entries in column A) by their respective atomic weights (from column B) and enter this value in column C in the table. Sum the entries in column C;

21、then individually divide the entries for each element in column C by the sum of column C. Enter this value in column D. This is the atomic fraction of that element. 3.3 Calculation of Phase Precipitations For the next series of calculations, reference will be made to cell locations in the table, suc

22、h that D1 refers to the value of the entry in column D, row 1 (for example, the atomic fraction chromium) and E5 is the residual matrix atomic percent of cobalt, adjusted for precipitation of second phases. 3.4 Boride and Carbide Precipitation 3.4.1 Chromium Multiply D1 by 0.97 and subtract the quan

23、tity (0.375)(D6) + (1.75)(D8), where: D1 is the atomic fraction of Cr D6 is the atomic fraction of B D8 is the atomic fraction of C Enter the result in E1. 3.4.2 Molybdenum From D3, subtract the quantity (0.75)(D6) + (0.167)(D8)(D3)/(D3+D14), where: D3 is the atomic fraction of Mo D6 is the atomic f

24、raction of B D8 is the atomic fraction of C D14 is the atomic fraction of W Enter the result in E3. SAE INTERNATIONAL AS5491C Page 5 of 7_ 3.5 Gamma Prime Precipitation 3.5.1 Nickel Add (0.525)(D6) to D19. Subtract from that sum the following quantity: 3(D4)+(0.03)(D1) + D16 + D2 + D15 (0.5)(D8) + (

25、0.5)(D13) + D17, where: D6 is the atomic fraction of B D19 is the atomic fraction of Ni D4 is the atomic fraction of Al D1 is the atomic fraction of Cr D16 is the atomic fraction of Cb D2 is the atomic fraction of Ti D15 is the atomic fraction of Ta D8 is the atomic fraction of C D13 is the atomic f

26、raction of V D17 is the atomic fraction of Hf Enter the result in E19 3.5.2 Vanadium Enter (0.5)(D13) in E13, where D13 is the atomic fraction of V. 3.5.3 Tungsten From D14, subtract the quantity (0.167) (D8)(D14)/(D3+D14), where: D14 is the atomic fraction of W D8 is the atomic fraction of C D3 is

27、the atomic fraction of Mo Enter the result in E14 3.5.4 Enter zero (0) in E2, E4, E6, E8, E15, E16, and E17. 3.5.5 Enter the value found in D5, D7, D9, D10, D11, D12, and D18 in the corresponding rows in column E. 3.6 Calculation of the Residual Matrix Composition 3.6.1 Sum the values in column E, a

28、nd enter at the bottom of column E. 3.6.2 Column F is the matrix atomic fractions. For each row, divide the value in column E by the sum of column E calculated in 3.6.1. 3.7 Calculation of Electron Vacancy Number 3.7.1 Multiply the matrix atomic fraction in column F by the individual elemental elect

29、ron vacancy numbers in column G, and enter the product in the corresponding row in column H. 3.7.2 The electron vacancy number for the alloy is the sum of the entries in column H, rounded to the nearest 0.01 unit. SAE INTERNATIONAL AS5491C Page 6 of 7_ 4. NOTES 4.1 The change bar ( l ) located in th

30、e left margin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document. PREPARED BY AMS COMMITTEE “F” SAE INTERNATIONAL AS5491C Page 7 of 7_