Nanocomposites and nanomaterials

Nanostructured AlNiCoFeCrTi high-entropy coating performed by Cold Spray
Hushchyk D.V., Yurkova  A.I., Chernyavsky V.V., Bilyk I.I., 
Nakonechnyy S.O. 
High-Temperature Materials and Powder MetallurgyDepartment, Igor Sikorsky Kyiv Polytechnic Institute,
Prospect Peremogy, 37, Kyiv-03056, Ukraine. 
E-mail: d.hushchyk@gmail.com 

In this work, solid-state mechanical alloying (MA) and cold spray (CS) [1] processes were applied to fabricate powder AlNiСоFeCrTi high-entropy alloy (HEA) [2] and then to produce HE coatings on steel substrate. 
Shot-time mechanical ball milling for 3 h has been employed to synthesize nanocrystalline equiatomic AlNiCoFeCrTi HEA of metastable supersaturated substitutional solid solution with bcc crystal structure. Although alloying is not complete at this milling time, it goes to completion during thermal annealing to achieve the alloy formation. XRD study on mechanically alloyed high-entropy AlNiCoFeCrTi alloy after thermal annealing at 1200 °C for 1 h revealed the formation of a three phase structure consisting of fcc and bcc solid solutions with fine precipitates of TiC (to 8 %). The alloy retains its nanocrystallinity even after heating. Coatings of 300 μm in thickness were deposited by the CS process using an air with a gun temperature and pressure of 450 °C and 0.9 MPa, respectively.
The coatings were dense (< 1 % porosity), and adherent (no interfacial cracks or debonds). X-ray diffraction and electron microscopy data show that the nanocrystalline powder microstructure is retained in the coating with no grain growth. The main benefit of cold-spraying is that the composite nanocrystalline structure in the interior of heavily deformed particles was believed to be actually the same as that of feedstock powder. The AlFeNiCoCrTi HE coatings exhibit 10.3±0.3 GPa in Vickers hardness. 
The experimental results confirm that CS can be used to produce HE coatings with low porosity. As a low-temperature deposition process, CS completely retained the HEA phase composition and nanostructure in the coating without any phase transformation. 

1.	Klinkov S.V., Kosarev V.F., Rein, M. Cold Spray Deposition, Signifcance of Particle Impact Phenomena // Aerosp. Sci. Technol.-2005.-9.-P. 582–591. 
2.	Murty B.S., Yeh J.W. and S. Ranganathan. High-Entropy Alloys.  Elsevier, 2014, 218 p.