This image shows the unique 'cross-lamellar microstructure' that can be developed in the niobium disilicide/molybdenum disilicide two-phase alloy by adding minute amounts of chromium and iridium. Image: Osaka University.Modern aircraft and power generation turbines rely on precision-machined parts that can withstand harsh mechanical forces in high-temperature environments. Especially as, in many cases, higher operating temperatures lead to more efficient performance. This motivates the search for new ultrahigh-temperature metal alloys that can maintain their shape and strength at temperatures where ordinary steel would melt.
Building on their research into a promising mixed alloy, a team of researchers at Osaka University in Japan have made a new breakthrough by adding two further metals to generate a unique structure that shows exceptional performance. They report their breakthrough in a paper in Scientific Reports.
"Our previous alloy was a blend of different transition metal disilicides, which were arranged in a lamellar structure," explains lead author Koji Hagihara. "Although the alloy's performance was good, it did not meet requirements for room temperature toughness and still showed some deformation at very high temperatures."
Transition metal disilicides are lightweight alloys with good high temperature resistance, ideally suited for ultrahigh-temperature applications. The Osaka team had previously combined two different transition metal disilicides – niobium disilicide and molybdenum disilicide – to form a microscopic structure with alternating layers of the different metal crystals. This ‘lamellar’ arrangement improved the alloy’s strength, but some problems remained because the strength was still low along the direction parallel to the two-phase interface.
Now, the team has added two new metals – chromium and iridium – to the alloy mixture to form a ‘cross-lamellar microstructure’. The new metals cause the growth of new crystals, which penetrate the crystal layer structure, similar to staples piercing a stack of paper. This effect prevents deformation parallel to the lamellar interface, considerably improving the mechanical performance of the alloy.
"Other researchers should take note of this unique cross-lamellar microstructure as a way of improving high-temperature creep strength and fracture toughness in ultrahigh temperature alloys," says group leader Takayoshi Nakano. "The performance of our alloy is now closer to meeting the demands of practical engineering applications. The efficiency gains from using ultrahigh temperature materials in gas turbines and jet engines could have a real impact on carbon dioxide emissions and global warming."
This story is adapted from material from Osaka University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.