Molybdenum silicides increases high-temperature strength of turbine blades

After investigating the properties of various compositions of molybdenum silicides, with and without additional ternary elements, material scientists at the Kyoto University in Japan found that molybdenum silicides improve turbine blade efficiency in ultrahigh-temperature combustion systems.

The nickel-based gas turbines that are commonly used to generate electricity in power plants today are often exposed to operating temperatures that can exceed 1,600 degrees Celsius. The drawback is these turbine blades melt at temperatures 200 degrees Celsius lower and so requires air-cooling to function at higher temperatures.

Turbine blades made out of materials with higher melting temperatures would require less fuel consumption and lead to lower CO2 emissions.

Previous research showed that fabricating molybdenum silicide-based composites by pressing and heating their powders – known as powder metallurgy – improved their resistance to fracturing at ambient temperatures but lowered their high-temperature strength, due to the development of silicon dioxide layers within the material.

The Kyoto University team fabricated their molybdenum silicide-based materials using a method known as “directional solidification,” in which molten metal progressively solidifies in a certain direction.

The team found that by controlling the solidification rate of the molybdenum silicide-based composite during fabrication and by adjusting the amount of the ternary element added to the composite, they could form a homogeneous material.

This resulting material starts deforming plastically under uniaxial compression above 1,000 degrees Celsius. Also, the material’s high-temperature strength increases through microstructure refinement.

Adding tantalum to the composite is more effective than adding vanadium, niobium or tungsten for improving the strength of the material at temperatures around 1,400 degrees Celsius.

The alloys fabricated by the Kyoto University team are much stronger at high temperatures than modern nickel-based super alloys as well as recently developed ultrahigh-temperature structural materials, the researchers report in their study published in the journal Science and Technology of Advanced Materials.