Modeling creep deformation of a two-phase TiAI/Ti 3 Al alloy with a lamellar microstructure
- PDF / 2,193,683 Bytes
- 11 Pages / 598 x 778 pts Page_size
- 70 Downloads / 222 Views
1.
INTRODUCTION
T H E low density and good oxidation resistance of TiA1 and Ti3AI ordered intermetallic alloys make them attractive candidate materials for high-temperature engineering applications, t~,2jHowever, these alloys possess poor ductility at low and intermediate temperatures and are susceptible to rapid fatigue-crack growth. [~] It has been shown by previous investigators that two-phase TiAI/Ti3A1 lamellar alloys exhibit an appreciably improved toughness and fatigue resistance compared to the constituent TiA1 and Ti3AI single-phase alloys, tl,31 Furthermore, Bartholomeusz, Yang, and Wert (BYW) 141 demonstrated that the minimum creep rate of a twophase TiA1/Ti3A1 lamellar alloy (referred to as the lamellar alloy in the present article) is lower than the creep rates of the constituent phases. The creep behavior of the TiA1/Ti3A1 lamellar alloy is not unique; several duplex alloys have been reported to possess lower creep rates than their constituent phases, most notably NiAI/Ni2A1Ti and Y/Y' nickel-base superalloys, tS,6,Tj It has been proposed that this phenomenon is a general one associated with duplex alloys possessing semicoherent interfaces.t5] Polvani et al.tS] suggested that the lower creep rate of the duplex NiA1/Ni2A1Ti alloy with respect to its constituent phases is due to the retardation of dislocation climb at semicoherent interfaces separating the two phases. It is possible that such a mechanism is occurring in the TiA1/Ti3A1 lamellar alloy, but alternate mechanisms could also account for the experimental observations. For example, the phases in the lamellar microstructure may possess lower steady-state creep rates than the corresponding constituent single-phase MICHAEL F. BARTHOLOMEUSZ, formerly with the Department of Materials Science and Engineering, University of Virginia, is Research Scientist, Reynolds Metal Company, Corporate Research and Development, Richmond, VA 23219. JOHN A. WERT, Professor, is with the Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903-2442. Manuscript submitted January l, 1994. METALLURGICALAND MATERIALS TRANSACTIONSA
alloys, as a result of enhanced work hardening. Powerlaw creep can be regarded as a competition between recovery and work hardening, tg,91 When a balance is achieved between these two processes, the material exhibits steady-state creep. Therefore, an increase in the work-hardening rate, or a reduction in the recovery rate, can have the effect of reducing the steady-state creep rate.
In a study of the elevated-temperature deformation characteristics of TiAI and Ti3A1 alloys, Rao and Tangri[~0] found that the alloys with lamellar microstructures exhibit substantially higher work-hardening rates than the single-phase alloys. There are several potential explanations for the higher work-hardening rates of TiAI and Ti3A1 within the lamellar microstructure. First, the interphase interfaces may provide a high density of dislocation sources in the lamellar alloy, as described by Appel et al. tm Second, segreg
Data Loading...
