Comments on Steady-state creep deformation of investment cast near-gamma titanium aluminide
- Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain)
- Univ. of California, Irvine (United States)
In a recent article, the creep behavior of a near-gamma Ti-48Al-2Nb-2Cr (at.%) cast alloy was investigated. The results and analyses are criticized as follows: Firstly, it is difficult to measure strain rates slower than 10[sup [minus]8]s[sup [minus]1] by conducting creep tests for only' 100 hours, since this corresponds to strains below 0.0036. Secondly, the activation energies for creep at 103 and 172 MPa calculated by the authors are incorrect. At 103 MPa, the activation energy for creep is [approximately]240 kJmol[sup [minus]1] rather than 300 kJmol[sup [minus]1] (data from Fig. 2). At 172 MPa, the stress exponents are clearly different from each other at the three temperatures; hence, an activation energy for creep associated with a single deformation mechanism cannot be determined. Thirdly, the authors claim that in the region where the stress exponent, n, is equal to three, dislocation pipe diffusion is controlling a stress-assisted diffusional creep mechanism...'. This is most likely incorrect since, when a diffusional creep mechanism (Nabarro-Herring/Coble) is dominating the deformation behavior, no dislocation motion is expected; as a consequence, the dislocation density should remain constant with applied stress in the low applied stress regime. In conclusion, it is difficult to determine the creep mechanism(s) of this alloy based on the data presented.
- OSTI ID:
- 6520722
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 28:7; ISSN SCRMEX; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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