The σ phase is rich in Ta. When the Ta concentration is less than 14%, σ does not interfere with the slip mechanism; when the Ta concentration is more than 15%, σ interferes with the slip mechanism. The coherent α-Co 3Ta phase forms at Ta concentrations of less than 15%, whereas incoherent γ-Co 2Ta forms only at higher Ta concentrations. The interface between σ and the matrix is an important factor in the failure mechanism.
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References
1.
Beattie, H.J., JR., and Hagel, W.C.: Compositional Control of Phases Precipitating in Complex Austenitic Alloys , Trans AIME233: 277, 1965.
2.
Hall, E., and Algie, S.: The Sigma Phase, J Inst Metals11 : 61, 1966.
3.
Silverman, R.; Arbiter, W.; and Hodi, F.: Effect of Sigma Phase on Co-Cr-Mo Base Alloys, Trans ASM49: 805, 1957.
4.
Sims, C.T.: A Contemporary View of Cobalt-Base Alloys, J Metals21: 27-42, 1969.
5.
Boesch, W.J., and Slaney, J.S.: Preventing Sigma Phase Embrittlement in Nickel-Base Superalloys, Metal Progress86: 109, 1964.
