Nanostructured AlNiCoFeCrTi high-entropy coating performed by cold spray

In this work, solid-state mechanical alloying (MA) and cold spraying (CS) processes were applied to fabricate powder AlNiCoFeCrTi high-entropy alloy (HEA) and then to produce HE coatings on steel substrate. Shot-time MA for 3 h has been employed to synthesize nanostructured equiatomic AlNiCoFeCrTi HEA of metastable supersaturated substitutional solid solution with bcc crystal structure. Although alloying is not complete at this shot 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 degrees C for 1 h revealed the formation of a three-phase structure consisting of ordered bcc phase with fine precipitates of intermetallic sigma-phase (FeCr) and titanium carbide TiC. The powder agglomerates resulted from annealing were grinded in a ball mill for 1 h. Nanostructured disordered bcc solid solution, TiC and sigma-phases are noticed after milling. Coatings of 450 mu m in mean thickness were deposited by the CS process using an air like a working gas, temperature and pressure of 450 degrees C and 0.9 MPa, respectively. The experimental results confirm that CS process 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. The AlFeNiCoCrTi HE coatings exhibit 10.3 +/- 0.3 GPa in Vickers hardness.