Nanograin Fe(Al) solid solution alloy coating was firstly produced through cold-spraying technology using mechanically alloyed powder. Then, the above-mentioned coating was annealed at different temperatures to explore its influence on the phase constitution, microstructure, microhardness and dry sliding wear property of the coatings. Results exhibited that an FeAl phase appeared in the coatings after 500 °C treatment and remained stable with increasing annealing temperature. The annealing temperature had a considerable effect on the microstructure, microhardness and wear behavior of the FeAl coating. The existing laminated structure in the as-sprayed coating gradually faded away with increasing temperature and finally obtained a dense coating microstructure with no particle interface when annealed above 950 °C. Nanograin began to evidently grow at temperatures over 800 °C. The microhardness of the FeAl coating stayed at 400 Hv₀.₁ at temperatures below 800 °C, then it quickly dropped to 300 Hv₀.₁ at 950 °C and remained nearly unchangeable up to 1100 °C. The dry sliding wear mechanism of the FeAl coating annealed at low temperatures below 700 °C was mainly delamination of the oxide layer and showed a high wear rate within the order of magnitude range of 10⁻⁴, whereas FeAl coatings annealed at high temperatures above 950 °C were worn by microploughing and little oxidation and exhibited very low wear rates within the order of magnitude range of 10⁻⁶.

In the present study, a nanostructured FeAl coating was prepared by cold spraying of ball milled powder. Annealing treatment was applied to the coating to investigate its effect on the microstructure, phase structure and microhardness of the cold-sprayed nanostructured FeAl coating. The results showed that the FeAl phase was kept unchangeable when the coating annealed at the temperature above 500oC. Annealing temperature significantly influenced the microstructure and microhardness of cold-sprayed FeAl coating. With raising annealing temperature, the lamellar structure in the as-sprayed coating disappeared and a dense coating microstructure with fully bonding of deposited particles at their interfaces was achieved after annealing at 950oC. Nanograin growth of the FeAl phase occurred at an annealing temperature higher than 800oC. The microhardness of cold-sprayed FeAl coating remained about 400 Hv0.1 at the annealing temperature below 800oC and decreased to 300 Hv0.1 at 1100oC.

The study aims to enhance the corrosion resistance and bioactivity of Mg alloy substrates through the development of a zinc/hydroxyapatite multi-layer (Zn/HA-ML) coating. The Zn/HA-ML coating was prepared by depositing a cold-sprayed (CS) Zn underlayer and a high-velocity suspension flame sprayed (HVSFS) Zn/HA multi-layer and was compared with the CS Zn coating and the Zn/HA dual-layer (Zn/HA-DL) coating. Phase, microstructure, and bonding strength were examined, respectively, by X-ray diffraction, scanning electron microscopy, and tensile bonding testing. Corrosion behavior and bioactivity were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion testing. Results show that the HVSFS Zn/HA composite layers were mainly composed of Zn, HA, and ZnO and were well bonded to the substrate. The HVSFS HA upper layer on the CS Zn underlayer in the Zn/HA-DL coating exhibited microcracks due to their mismatched thermal expansion coefficient (CTE). The Zn/HA-ML coating exhibited good bonding within different layers and showed a higher bonding strength of 27.3 ± 2.3 MPa than the Zn/HA-DL coating of 20.4 ± 2.7 MPa. The CS Zn coating, Zn/HA-DL coating, and Zn/HA-ML coating decreased the corrosion current density of the Mg alloy substrate by around two–fourfold from 3.12 ± 0.75 mA/cm² to 1.41 ± 0.82mA/cm², 1.06 ± 0.31 mA/cm², and 0.88 ± 0.27 mA/cm², respectively. The Zn/HA-ML coating showed a sixfold decrease in the corrosion current density and more improvements in the corrosion resistance by twofold after an immersion time of 14 days, which was mainly attributed to newly formed apatite and corrosion by-products of Zn particles. The Zn/HA-ML coating effectively combined the advantages of the corrosion resistance of CS Zn underlayer and the bioactivity of HVSFS Zn/HA multi-layers, which proposed a low-temperature strategy for improving corrosion resistance and bioactivity for implant metals.