The influence of microstructure on creep deformation in near-gamma TiAl alloys. Ph.D. Thesis
The influence of microstructure on creep deformation has been examined in the near-gamma TiAI alloys Ti-49Al-1V and Ti-48Al-1V-0.3C between 760 C and 870 C in the stress range of 50 MPa to 200 MPa. A systematic approach was made to develop methods to control microstructural morphologies and alpha(sub 2) volume fraction has been conducted. By carefully controlling thermo-mechanical processing parameters, the influence of solution temperature, cooling rate, and secondary heat treatment on volume fraction and morphology of alpha(sub 2) has been determined. Microstructure was shown to have a significant influence on the creep behavior of the near-gamma TiAl alloy Ti-49Al-1V, with a fully lamellar having the highest creep resistance. Overall creep resistance was by the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. The decrease in creep resistance of the duplex microstructure, compared to the near-gamma microstructure can be explained by an increase in dislocation mobility within the equiaxed gamma constituent. The high creep resistance of the fully lamellar microstructure is attributed to the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion. The influence of interstitial strengthening and microstructure on creep deformation has been examined in the near-gamma TiAl alloy Ti-48Al-1V-0.3C. Significant improvement in creep resistance was observed in this alloy compared with the Ti-49Al-1V alloy containing low levels of carbon (0.07 at percent). The degree of strengthening resulting from the addition of carbon was greater in the near-gamma and duplex microstructures than in the fully lamellar microstructure. A decrease in stress exponent from 4 to 3 occurs and the formation of sub-boundaries is inhibited with the addition of carbon in both the duplex microstructure and near-gamma microstructures.
- Research Organization:
- Univ. of Michigan, Ann Arbor, MI (United States)
- OSTI ID:
- 102046
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: 1994
- Country of Publication:
- United States
- Language:
- English
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