WC-Co cermet materials serving as protective coatings are widely used in many fields. Conventional WC-17Co coatings were formed in high-velocity oxygen-fuel (HVOF), warm spraying (WS), and cold spraying (CS), respectively. Deposition behavior of a single WC-17Co particle, as well as the microstructure, microhardness, fracture toughness, and abrasive wear of WC-17Co coatings formed in various spraying ways were investigated. The results show that the deposition behavior of a single WC-17Co particle was different after it was deposited onto a Q235 steel substrate in various spraying ways. The WC-17Co splat deposited by HVOF showed a center hump and some molten areas, as well as some radial splashes presented at the edge of the splat. The WC-17Co splat deposited by WS presented a flattened morphology with no molten areas. However, the WC-17Co splat deposited by CS remained nearly spherical in shape and embedded into the substrate to a certain depth. All the WC-17Co coatings had the same phase compositions with that of feedstock. The microstructure of all the WC-17Co coatings was dense with no cracks or abscission phenomena between the coatings and substrate. Moreover, fine WC particles were formed in the coatings due to the fracture of coarse WC particles, and the content of fine WC particles in the cold-sprayed coating was significantly more than the other coatings. A stripe structure was formed by the slippage of fine WC particles with a plastic flow of Co binder in the warm-sprayed and cold-sprayed coatings. More fine WC particles, as well as the stripe structure, in the coatings were conducive to improve the microhardness and fracture toughness of the coating. The microhardness and fracture toughness of the cold-sprayed WC-17Co coating were the highest among the coatings. The main wear mechanism of all coatings was the groove and some peel-offs. The cold-sprayed WC-17Co coating with the lowest wear loss presented the highest wear resistance among the coatings.

In this work, 3D printed polylactic acid (PLA)/polycaprolactone (PCL) nanocomposites with favorable thermo-responsive cyclic shape memory effects (SMEs) and crystallization and mechanical properties were fabricated using a two-step method. First, an isocyanate-terminated PCL diol (PCL-NCO) was synthesized through the reaction between isocyanate groups of hexamethylene diisocyanate and active hydroxyl groups of PCL diol, and its physicochemical properties were characterized. A PLA/PCL blend with a PCL content of 50 wt% was fabricated via fused filament fabrication (FFF) 3D printing, and the influence of the PCL-NCO on the SME of the PLA/PCL blend was studied. The results indicated that the PCL-NCO significantly improved the cyclic shape memory performance of 3D printed PLA/PCL blends and was proved to be an effective interface compatibilizer for the blend system. Subsequently, the structure and properties of 3D printed PLA/PCL nanocomposites were investigated in detail by adding cellulose nanocrystal-organic montmorillonite (CNC-OMMT) hybrid nanofillers with different contents. It was found that the hybrid nanofillers greatly enhanced crystallization and mechanical properties of the nanocomposites due to adequate dispersion. The modification of the PLA/PCL blend and the preparation of the 3D printed nanocomposite can not only prolong the service life of a shape memory polymer product, but also broaden its application scope in advanced fields.

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HA composite coatings added reinforcement phases could improve the mechanical properties and bonding strength of the coatings. Cold spraying is a feasible surface technology for preparing HA composite coatings. In order to investigate the influence of cold spraying parameters on the deposition behavior of a single HA/Ti composite particle, numerical and experimental investigation of gas-particle two-phase flow in cold spraying nanostructured HA/Ti composite particle were investigated in this study. The results show that the influence of different temperatures and pressures on static pressure was not significant. The effects of gas pressure on the static temperature were tiny under the same inlet temperature and different pressure conditions; however, the static temperature in the entire spray gun cavity increased as the inlet temperature increased under the same pressure and different inlet temperature conditions. There is little effect of gas pressure on the axial velocity of gas flow in the spray gun cavity; however, the axial velocity of gas flow increased with the increase in gas temperature. Meanwhile, the axial velocity of gas flow gradually increases throughout the spraying process. At a gas temperature of 573 K and 973 K, the maximum axial velocities of a gas flow at gas pressure of 2.2 MPa were 778 m/s and 942 m/s, respectively. There is little effect of gas pressure on the axial velocity of HA/30 wt.% Ti particles under the same gas temperature. The axial velocity of HA/30 wt.% Ti particles increased with the increase in gas temperature under the same gas pressure condition. The axial velocity of composite particles decreased with the increase in the particle size under the same gas pressure and gas temperature. At a gas temperature of 573 K and 973 K, the minimum axial velocity of HA/30 wt.% Ti particles with a particle size of 30 μm at a gas pressure of 2.2 MPa was 435 m/s and 467 m/s, respectively. A certain deformation of splats occurred after impacting the substrate, and the splats adhered to the surface of the Ti6Al4Vsubstrate, clearly presenting a flat shape with a central hump surrounded by a ringy band. At a gas temperature of 973 K, particles generated more severe deformation with more cracks and ejecta phenomenon. The splats attached to the substrate were increased as the gas temperature increased.

The influence of post-process heat treatment on cold-sprayed Zn coatings on the Mg alloy substrate was investigated at different temperatures (150, 250, and 350 °C) and times (2, 8, and 16 h). Phase, microstructure, microhardness, and tensile strength of Zn coatings were analyzed before and after heat treatment. Corrosion properties of Zn coatings after heat treatment were investigated in simulated body fluid by using potentiodynamic polarization and immersion testing. Results show that although the heat treatment presented little effect on phase compositions of Zn coatings, the full width at half maxima of the Zn phase decreased with the heat temperature and time. Zn coatings presented comparable microstructures before and after heat treatment in addition to the inter-diffusion layers, and the inter-diffusion layer was dependent on the heat temperature and time. Both the thickness and the microhardness of inter-diffusion layers were increased with the heat temperature and time, with the largest thickness of 704.1 ± 32.4 μm and the largest microhardness of 323.7 ± 104.1 HV0.025 at 350 °C for 2 h. The microhardness of Zn coating was significantly decreased from 70.8 ± 5.6 HV0.025 to 43.9 ± 12.5 HV0.025, with the heat temperature from the ambient temperature to 350 °C, and was slightly decreased with the heat time at 250 °C. Although the tensile strength of Zn coating was slightly increased by heat treatment, with the highest value of 40.9 ± 3.9 MPa at 150 °C for 2 h, excessive heat temperature and time were detrimental to the tensile strength, with the lowest value of 6.6 ± 1.6 MPa at 350 °C for 2 h. The heat temperature and heat time presented limited effects on the corrosion current and corrosion ratio of the Zn coatings, and Zn coatings before and after heat treatment effectively hindered the simulated body fluid from penetrating into the substrate. The corrosion behavior of Zn coatings was discussed in terms of corrosion products and microstructures after immersion.