NUST MISIS researchers reported that samples of aluminum composites treated with carbon nanofibers, have shown a 20 percent increase in hardness and significant changes in material structure at the micro level. Their study results were published in the Journal of Nanomaterials.
Aluminum and alloys derived from it are among the key materials in modern industry and technology, experts said. This accessible, lightweight, and versatile metal is essential for transport, construction, electronics, and aerospace spheres.
However, the scientists note that further enhancement in the mechanical properties of aluminum alloys is required to increase the specific weight-to-strength ratio. According to them, bringing the mechanical characteristics and functional properties of the materials in line with the requirements of advanced modern technology is an urgent task of today.
“Generally speaking, there are two main ways to improve the performance properties of an alloy: to create a new composite material with a more complex composition or to treat the surface of the finished products by applying an additional coating. We have combined both approaches and achieved the synergistic effect of several factors in the interaction of micro-sized aluminum oxide and nano-scale carbon fibers”, explained Ivan Pelevin, Researcher at NUST MISIS’ Catalysis Lab.
Researchers have chosen cast and 3D-printed aluminum samples as the basis and increased their surface properties by applying a composite coating using the cold-spray method.
Pelevin explained that the Al-Al2O3-UNV composite coating is based on a powder mixture from the industrial raw material for aluminum production – alumina, or aluminum oxide – with the addition of 30 percent pure metal particles. During the synthesis process, he said, the aluminum particles are crushed as they collide with the harder oxide, filling the voids in its structure. This composition of hard and ductile particles ensures a strong bonding of the coating on the surface of the aluminum detail.
On the other hand, the nano-scale carbon fibers permeate the space already between the metal powder particles, further increasing the density at micro level, dramatically reducing the number of cracks and voids and increasing the hardness and strength of the applied coating, the scientists explained. The introduction of only 1.5 % carbon nanofibers has increased the hardness of the coating by 20 %.
A third active factor, they said, was the high frictional properties of carbon which also contributed to the formation of a dense, defect-free coating structure through “lubrication” during particle impact. Moreover, the carbon addition to the coating potentially improves frictional properties and wear resistance through in-situ lubrication (self-lubrication).
The scientists pointed out that on top of these factors, the correct method of synthesis was also important.
“The synthesis of coatings by other methods raises the problem of phase transitions, which is especially painful for aluminum with its low melting point. The metal particles on the spraying surface melt and solidify again - that is, the structure of the substance is disturbed, and additional stress appears inside the material. That is why we used cold-spray method, and clearly demonstrated the advantages of such a solution,” Ivan Pelevin added.
Researchers are convinced that their study, conducted with support of the Russian Science Foundation, is of great practical importance not only for improving the properties of a particular aluminum alloy but also for many details of various purposes. A particular attention is paid to the processing of the material exactly after 3D-printing, because it is the most actual and demanded scientific task. The research team plans to produce composites with the required microstructure for energy, biomedical, and other purposes in the near future.