Scientists at Japan's Kyoto University have tested various compositions of molybdenum silicides for use at turbine blades, improving the strength of the material at temperatures around 1,400 degrees Celsius. Research shows that adding tantalum to the composite helps boost material resilience.
Nickel-based turbine blades, used in such combustion systems, already melt at temperatures 200 degrees Celsius lower and hence require air-cooling. Yet, operating temperatures of gas turbine combustion systems can occasionally exceed 1,600 degrees Celsius.
Researchers at Kyoto University found out that fabricating molybdenum silicide-based composite - by pressing and heating their powders (powder metallurgy) - improves resistance to fracturing at ambient temperatures. However, this process also lowers the material’s high-temperature strength, owing to the inclusion of silicon dioxide layers within the material.
Using ‘directional solidification’, the team managed to fabricate their molybdenum silicide-based materials. The team found that a homogeneous material could be formed by controlling the solidification rate of the composite during fabrication, and by adjusting ternary elements added to the composite.
Tantalum increases material strength
“The new material only starts to deform plastically under uniaxial compression above 1,000 degrees Celsius,” researchers said, adding 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 1400 degrees Celsius,” they pointed out.
In a report, published in the Journal Science and Technology of Advanced Materials, the researchers pointed out that alloys fabricated at Kyoto University are “much stronger at high temperatures than modern nickel-based superalloys as well as recently developed ultrahigh-temperature structural materials.”