Backside crack radius for MoSiB- and NbSi-base materials at room temperature and 1200 °C.
Pratt & Whitney has been developing a molybdenum-base alloy and GE has been developing a niobium-base alloy under the Integrated High Performance Turbine Engine Technology’s (IHPTET) Revolutionary Blade Material program, which is developing advanced materials to replace today’s superalloys in the hot sections of turbine engines. The IHPTET program had a milestone to compare the status and potential of these materials by July 2002. As one of several criteria used in the evaluation, the NASA Glenn Research Center was asked by the Air Force to perform ballistic impact testing to simulate foreign object damage. The purpose of this work was to examine the ballistic impact response of the two candidate alloys as one of several critical properties needed for engine application.
Ballistic testing of NbSi and MoSiB, as well as of samples of NbSi that had been coated with an oxidation-resistant coating, was performed at room temperature and 1200 °C at a variety of impact energies. The backside crack radius, after impact testing, was measured and plotted as a function of impact energy. At 1200 °C, both silicide materials performed better than they did at room temperature. This is somewhat surprising, because previous research on other intermetallics, NiAl and TiAl, did not show strong temperature dependence. The improvement was quite dramatic for NbSi but more moderate for MoSiB. The plot illustrates that the niobium alloy was clearly more impact resistant than the molybdenum alloy at both room and elevated temperature.
On the basis of these preliminary results, the NbSi material probably has sufficient impact resistance to perform as a high-pressure turbine blade. Its room temperature behavior is adequate, and its high-temperature behavior is very good, far surpassing any other advanced intermetallic or ceramic tested in our labs. A more accurate assessment of NbSi would require more exact knowledge of the actual engine environment and a series of tests to examine thermal history effects and postimpact mechanical performance. However, the current MoSiB alloy is inadequate for rotating parts, even if the improved high-temperature data are taken into account, and the alloy would need further refinement to accommodate potential foreign or domestic impact damage.
Glenn contacts: Susan Draper, 216-433-3257, Susan.L.Draper@nasa.gov
Authors: Susan L. Draper and Dr. Michael V. Nathal
Headquarters program office: OAT
Programs/Projects: HOTPC
Last updated: June 25, 2003
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