Compared with gasoline, natural gas combustion is cleaner and more efficient, producing about 25% less carbon dioxide, and the cost of refining and processing is also relatively low. Therefore, natural gas powered vehicles are increasingly concerned. However, due to the high combustion temperature of natural gas, the requirements for metal engine parts are much higher.
According to foreign media reports, researchers at the University of Virginia developed a new high temperature resistant low-cost alloy by combining nickel powder and graphene sheet, and applied for a patent. This new metal matrix composite can maintain integrity at 1000 ℃, or it will become a good choice for natural gas automobile engine materials.
Two classical problems in the field of superalloys are first explained. The influence of "active elements" (usually yttrium and zirconium) in superalloys; the role of water vapor in corrosion protection. The researchers showed the relationship between the two factors, and demonstrated how the active elements in the alloy promote the growth of the protective layer of alumina. It is because of these active elements that the protective layer of alumina grows inward, thus promoting the transfer of water vapor from the surrounding environment to the alloy substrate. The interaction between active elements and water promotes the formation of metastable "disordered" nano alumina layer.
When designing materials, researchers draw inspiration from nature, such as mother of pearl shells. "They have layers of structure." Mother of pearl is composed of hexagonal aragonite sheets, and its strength and toughness are very rare in engineering materials. In the manufacture of most composite materials, the combination of the two alloys will lead to the loss of ductility or toughness of most composite materials. However, with the structure similar to aragonite, the strength of graphene and nickel composite can be increased by 73%, and the tensile strength can only be reduced by 28%. The composite can even maintain high hardness at 1000 ℃.
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