SBIR-STTR Award

The demand for improvement in the perf ormance and ef f iciency of modern turbines requires the development of advanced materials which retain high strength, creep and oxidation resistance at increasingly elevated temperatures. Many materials meet the high-temperature criteria, for example ceramics, some intermetallic compounds and metallo-ceramics such as MoSi2, but suffer from a lack of toughness, either because of persistent brittleness at high temperatures or because a ductile-brittle transition (DBT) takes place between operating and room temperatures. Critical to the utility of these materials is an understanding of the mechanisms responsible for the DBT and specific indication of how the impact of the DBT can be minimized or avoided. This proposal will focus directly on MOS'21 an MC material which, at high temperatures, combines the strength typical of ceramics with the toughness of metals. The proposed work will use an innovative, inter-disciplinary technique (combining fundamental quantum mechanics with materials science) to evaluate the temperature dependence of dislocation nucleation and mobility and hence determine the origin of the DBT in MOS'2. From this a prescription will be developed for increasing the fracture toughness of MOS'2 by microalloying to eliminate or control the DBT.

Keywords:
Toughness Ductile-Brittle Transition Unstable Stacking Fault Generalized Stacking Fault Toughness

The planned program willuse firest-principles density-functional calculations to determine microalloying additions which will lower the ductile-brittle transition temperature in Molybdenum disilicide and/or other refractory silicides to room temperature. A searchable dataase of refractory silicide properties will be prepared and placed on the market. Selected silicides will be produced in small quanitities; the calculated property modifications will be confirmed by single crystal experiments. Polycrystalline processing methods will be developed and the resulting compacts tested in the laboratory for mechanical properties. The result will be a low-cost, ductile material with exceptional tolerance of high temperatures. A major gas turbine manufacture will provide specifications for a non-critical turbine componenet. Scale-up methods will be developed and prototype components will be produced from one of the lab-tested silicides. The prototype will be subjected to test-bed service evaluation. In the Option Phase, the prototype component will be evaluated in retrofit and new service environments.

Keywords:
Silicides Density Functional Theory Ceramics Ductile-Brittle Transition Microalloying