Thermodynamics of the superalloys
- PDF / 670,037 Bytes
- 7 Pages / 594 x 774 pts Page_size
- 24 Downloads / 253 Views
I.
INTRODUCTION
O V E R the past 40 years a host of alloys have been developed for service under extreme conditions of temperature and stress. These alloys are collectively known as the superalloys. Without doubt the development of this class of alloys represents the crowning metallurgical achievement. Not only has this development involved alloys having a dozen components but it also required considerable development in all phases of processing and fabrication. The program has been very expensive in terms of manpower, materials, and facilities. Three related developments in the field of thermodynamics will have a major impact on developing and understanding complex alloys, including the superalloys. First, the analytical representations that have been shown to be adequate for binary systems have also been shown to represent higher order systems adequately. Second, considerable effort has been expended in deriving sets of parameters for binary systems that are components of this complex class of alloys. And third, computer programs are being developed that can carry out the required calculations. Many people have been involved in this effort in thermodynamics. The reader's attention is directed to the new international journal, CALPHAD, which is devoted solely to this effort and which reports most of the work. The specific effort reported here is the product of a computer program that-we have written to characterize the liquid and the body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp) solid solutions composed of combinations of C, A1, Si, Ti, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, and W by using parameters derived by Kaufman and Nesor. 1-7 The parameters for the four solutions for each binary pair are not all presently available, but, as we will show, the data base is sufficiently complete to permit useful calculations on complex alloys. Specifically, we report free energy values for the fcc superalloy matrices containing A1, Ti, Cr, Fe, Co, Ni, Mo, and W. This information is useful in predicting the interaction of such alloys with external media as well as predicting what phases can form during internal equilibration. R . O . WILLIAMS is with Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830. Manuscript submitted August 6, 1981.
METALLURGICAL TRANSACTIONS A
Many calculations have been reported on ternary systems and occasionally quaternary systems having components of the superalloys, but these are the first calculations using a substantially larger number of components. With an increasing number of components the complexities increase because the number of terms increases, but no additional principles are involved. The program we used is presently limited to 13 components by the availability of parameters. The program has also been expanded on a limited basis for calculating the equilibrium between any two of the four solution phases, but such results are not part of the present report. When adequate thermodynamic models of the intermediate phases ar
Data Loading...
