Engineered materials for application in severe metallurgical environments: Tantalum-carbon alloy development. Ph.D. Thesis
A suite of investigations has been completed to develop and demonstrate a construction material for use in severely corrosive metallurgical processing environments. The material is a tantalum-base alloy with inclusions of Ta2C. Alloy development work involved multi-step thermal processing to invoke specific microstructural features. The kinetics of carbide formation from supersaturated solid solutions of carbon in tantalum were established. Performance evaluation of the alloy was conducted and the alloy has been demonstrated to outperform any previously studied metallic construction material used in pyrometallurgical processing of plutonium. Specific microstructural features of the alloy have been identified which provide the extreme corrosion resistance. Grain boundary occupancy by the Ta2C phase is associated with the corrosion resistance to liquid metal. Precipitation from the supersaturated condition invokes a microstructure with the most significant grain boundary delineation by carbide inclusions and hence provides the most corrosion resistant attributes. It has been experimentally proven that the precipitate growth rate is not dictated solely by the diffusion rate of the interstitial species and is more complex. The observed growth rate of carbide precipitates involves several competing effects. An expression which describes precipitate growth within the grain boundary is presented: W =((delta)X(0))/((X(b) - X(e)))square root of(t(0.0337 e(exp ({minus}51300/RT)))), where W is the width of the precipitate, delta(X(0)) is the degree of supersaturation, X(b) is the mole fraction carbon in the precipitating phase, and X(e) is the equilibrium carbon mole fraction in the matrix at the aging (precipitation) temperature. The engineered material investigated in this work has exceptional corrosion resistance to liquid metals due to occupancy of grain boundary regions by the extremely refractory phase Ta2C.
- Research Organization:
- Colorado School of Mines, Golden, CO (United States)
- OSTI ID:
- 236783
- Report Number(s):
- N--96-21547; NIPS--96-34629
- Country of Publication:
- United States
- Language:
- English
Similar Records
Role of microstructure in caustic stress corrosion cracking of Alloy 690
Precipitation reactions in Inconel alloy 600 and their effect on corrosion behavior. Paper No. 112