Development of ODS-Fe{sub 3}Al alloys
- Oak Ridge National Lab., TN (United States)
The overall goal of this program is to develop an oxide dispersion-strengthened (ODS) version of Fe{sub 3}Al that has sufficient creep strength and resistance to oxidation at temperatures in the range 1000 to 1200 C to be suitable for application as heat exchanger tubing in advanced power generation cycles. The main areas being addressed are: (a) alloy processing to achieve the desired alloy grain size and shape, and (b) optimization of the oxidation behavior to provide increased service life compared to semi-commercial ODS-FeCrAl alloys intended for the same applications. The recent studies have focused on mechanically-alloyed powder from a commercial alloy vendor. These starting alloy powders were very clean in terms of oxygen content compared to ORNL-produced powders, but contained similar levels of carbon picked up during the milling process. The specific environment used in milling the powder appears to exert a considerable influence on the post-consolidation recrystallization behavior of the alloy. A milling environment which produced powder particles having a high surface carbon content resulted in a consolidated alloy which readily recrystallized, whereas powder with a low surface carbon level after milling resulted in no recrystallization even at 1380 C. A feature of these alloys was the appearance of voids or porosity after the recrystallization anneal, as had been found with ORNL-produced alloys. Adjustment of the recrystallization parameters did not reveal any range of conditions where recrystallization could be accomplished without the formation of voids. Initial creep tests of specimens of the recrystallized alloys indicated a significant increase in creep strength compared to cast or wrought Fe{sub 3}Al, but the specimens failed prematurely by a mechanism that involved brittle fracture of one of the two grains in the test cross section, followed by ductile fracture of the remaining grain. The reasons for this behavior are not yet understood. The cyclic oxidation kinetics of ODS-Fe{sub 3}Al alloys made from commercially-produced powder indicated a decrease in the tendency for scale spallation at 1100 and 1200 C compared to equivalent ORNL-produced alloys. The overall oxidation rate at 1100 C in terms of total oxygen consumption as a function of time was essentially the same as for a semi-commercial ODS-FeCrAl alloy. Hence, this improvement indicates an increase in the oxidation-limited lifetime compared to both ODS-Fe{sub 3}Al alloys prepared at ORNL, and to the ODS-FeCrAl alloy.
- Research Organization:
- Oak Ridge National Lab., TN (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 330684
- Report Number(s):
- CONF-9705115--PROC.; ORNL/FMP--97/1; ON: DE98007329
- Country of Publication:
- United States
- Language:
- English
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