In order to improve the interface and mechanical properties of aramid fiber (AF)-reinforced epoxy resin (EP) composites (AF/EPs), the surface modification of AF was carried out with atmospheric pressure air plasma, and the effects of plasma treatment time and discharge power on the AF surface and the interface and mechanical properties of AF/EPs were investigated. The results show that, when plasma treatment time was 10 min and discharge power was 400 W, AF showed the best modification effect. Compared to the unmodified material, the total content of active groups on the surface of AF increased by 82.4%; the contact angle between AF and EP decreased by 20%; the interfacial energy and work of adhesion increased by 77.1% and 19.1%, respectively; the loss of AF monofilament tensile strength was controlled at only 8.6%; and the interlaminar shear strength and tensile strength of AF/EPs increased by 45.5% and 10.4%, respectively. The improvement in AF/EP interfacial and mechanical properties is due to the introduction of more active groups on the AF surface with suitable plasma processing parameters, which strengthens the chemical bonding between the AF and EP matrix. At the same time, plasma treatment effectively increases the surface roughness of AF, and the mechanical meshing effect between the AF and EP matrix is improved. The synergistic effect of chemical bonding and mechanical meshing improves the wettability and interfacial bonding strength between the AF and EP matrix, which enables the load to be transferred from the resin to the fiber more efficiently, thereby improving the mechanical properties of the AF/EP.

The TiB₂ reinforced Inconel 718 alloy composite coatings were prepared on carbon steel by laser cladding. The energy input (the ratio of laser power and scanning speed, E) was introduced to investigate the effects of process parameters on geometrical characteristics, microstructure and tribological properties of composite coatings. The results show that the dilution rate decreases and the contact angle increases, respectively, as E decreases from 200.00 J/mm to 80.00 J/mm, which causes the decrease of the boding strength from 1.91 GPa to 0.39 GPa. The composite coatings contain the phases of γ-(Ni, Fe), Laves, TiB₂, TiB, TiC, Ni₃B, CrB₄ and Cr₂₃C₆. As E decreases from 200.00 J/mm to 133.33 J/mm, the primary dendrite arm spacing (PDAS) and the Laves content of the composite coating decrease for the increase of cooling rate, leading to the increase of microhardness, the improvement of tribological properties and the change of wear mechanism from the severe multi-plastic deformation wear, adhesive wear and oxidative wear to the slight abrasive wear. However, as E decreases from 133.33 J/mm to 80.00 J/mm, for the weak Marangoni convection, TiB₂ particles are prone to aggregate in the top of the composite coating which causes the increase of the PDAS and the Laves content, leading to the decrease of the microhardness and the degradation of tribological properties, and the wear mechanism change to the multi-plastic deformation wear and abrasive wear gradually.

The effect of TiB₂ particles content (10–40 wt.%) on the microstructure, mechanical properties and tribological properties of TiB₂-reinforced Inconel 718 alloy composite coatings by laser cladding was investigated. From the perspective of solidification thermodynamics and dynamics, when the TiB₂ particles content increases from 10 to 30 wt.%, the cooling rate increases for the increase in thermal conductivity and thermal diffusion coefficient, leading to the decrease in dendrite size, and the uniformity of TiB₂ particles becomes better for the decrease in the critical capture speed of the solid–liquid interface, causing the improvement of microhardness and tribological properties. However, when the TiB₂ particles content is too high (40 wt.%), the cooling rate decreases for the increase in heat released by solidification, so the dendrite size increases, and the Marangoni convection is too weak to drive the rearrangement of TiB₂ particles, leading to the heterogeneous microstructure, large fluctuation of microhardness and the deterioration of tribological properties. When the TiB₂ particles content is 30 wt.%, the composite coating has the finest and densest dendrites and evenly distributed TiB₂ particles, the bonding strength is as high as 1.714 GPa, the microhardness is up to 844.33 HV_0.2, which is 2.98 times that of Inconel 718 alloy coating, and the friction coefficient and the wear rate are 0.355 and 9.12 × 10⁻⁷ g/(N·m), which are 22.99% and 83.86% lower than those of the Inconel 718 alloy coating.

In order to improve the interfacial properties of graphene oxide (GO) and epoxy resin (EP), hyperbranched polyesters with terminal carboxyl (HBP) non-covalently functionalized graphene oxide (HBP-GO) was achieved by strong π-π coupling between hyperbranched polyesters and GO nanosheets. The effects of non-covalent functionalization of GO on the dispersibility, wettability and interfacial properties were analyzed. The mechanical properties and enhancement mechanism of HBP-GO/EP composites were investigated. The results show that the hyperbranched polyesters is embedded in the GO layer due to its highly branched structure, which forms the steric hindrance effect between the GO nanosheets, effectively prevents the agglomeration of GO nanosheets, and significantly improved the dispersibility of GO. Simultaneously, the contact angle of HBP-GO with EP is reduced, the surface energy, interfacial energy and adhesion work are increased, then the wetting property of HBP-GO is significantly improved. The main toughening mechanism of HBP-GO is microcrack deflection induced by HBP-GO and plastic deformation of the EP matrix. In the microcrack propagation zones, HBP-GO may produce the pinning effect near the microcrack tips and change their stress state, resulting in microcrack deflection and bifurcation. So, the microcrack propagation path is more tortuous, which will consume much more fracture energy. Therefore, the mechanical properties of the HBP-GO/EP composites are greatly improved.