Fiber-reinforced composite component with improved interfacial adhesion through hybrid nanocoating

Abstract

A fiber-reinforced composite component consisting of a carbon fiber and a matrix material, wherein the carbon fiber is provided with a hybrid nanocoating consisting of an inner layer of carbon nanotubes that adhere directly to the fiber surface and an outer layer of pyrolytic carbon that conformally covers the carbon nanotubes.

Description

AREA OF INVENTION

[0001] The invention relates to a fiber-reinforced composite component with a particular focus on improved interfacial load transfer and durability in structures that use carbon fibers with advanced surface modification. BACKGROUND OF THE INVENTION

[0002] Fiber-reinforced composites, particularly those with carbon fibers, are crucial in the aerospace, civil engineering, and automotive industries due to their exceptional strength-to-weight ratio. However, a significant limitation to fully exploiting the potential of these materials lies in the weak bond between the reinforcing fiber and the surrounding polymer matrix. Commercial carbon fibers are typically coated with a polymer that exhibits poor chemical and mechanical compatibility with high-performance matrices. This weak fiber-matrix interface significantly compromises the overall mechanical integrity, load-transfer efficiency, and long-term durability of the finished composite component.Existing surface treatments often involve complex, multi-stage processes or fail to achieve comprehensive improvements in both mechanical adhesion and environmental resistance across various matrix systems. Therefore, there is a persistent need for an improved, scalable carbon fiber surface architecture that robustly enhances interfacial adhesion and protects the underlying fiber, thereby maximizing composite performance. SUMMARY OF THE INVENTION

[0003] A fiber-reinforced composite material is disclosed, comprising a matrix material and an embedded carbon fiber, wherein the carbon fiber features a novel, two-layer hybrid nanocoating structure deposited on its outer surface. This crucial structure consists of an inner layer of carbon nanotubes (CNTs) grown directly onto the prepared carbon fiber surface and a thin, conformal outer layer of pyrolytic carbon (PyC) deposited over the entire CNT network. This specific arrangement fundamentally alters the fiber-matrix interface, resulting in a transition from a weak adhesive bond to a robust, large-surface-area mechanical and chemical interweaving, thereby significantly enhancing interfacial shear strength (IFSS) and fiber pull-out resistance.

[0004] The inner CNT layer provides exceptional surface roughness and a three-dimensional interlocking mechanism that mechanically bonds the coating to the fiber and increases the contact area. Simultaneously, the subsequent outer PyC layer acts as a rigid, chemically inert, and highly compatible intermediate layer that effectively fixes the CNT structure and provides a clean, reactive carbon surface for optimal chemical bonding with the surrounding polymer matrix. This integrated hybrid nanocoating thus significantly improves the crucial mechanical properties of the composite, including enhanced load transfer and high resistance to crack propagation and environmental influences. This enables the production of lighter, stronger, and more reliable composite components suitable for demanding structural applications. DETAILED DESCRIPTION

[0005] This invention describes a fiber-reinforced composite component characterized by a carbon fiber filament with an integrated hybrid nanocoating system for improving interfacial adhesion. After post-treatment, the carbon fiber itself serves as the primary reinforcing element, embedded in a structural matrix. The first crucial feature of the component is the substrate: a commercially available carbon fiber that has undergone a cleaning step to remove the commercial polymer sizing. This preparation ensures that the subsequent nanocoating layers bond directly and chemically to the untreated carbon surface, thus maximizing the stability and effectiveness of the entire coating system.

[0006] The first active layer of the hybrid nanocoating system consists of an inner layer of high-density carbon nanotubes (CNTs). These CNTs are aligned vertically or semi-vertically on the purified carbon fiber surface. The function of this layer is to drastically increase the effective surface area of ​​the fiber and create a highly rough, three-dimensional topography, which is essential for the mechanical interlocking mechanism within the composite material.

[0007] A specific precursor state is required for the formation of the inner CNT layer. In an intermediate step, the purified fiber can be saturated with a catalyst precursor (e.g., a salt solution of iron, nickel, or cobalt). This precursor is thermally decomposed, resulting in nanoscale catalytic metal islands. These serve as nucleation sites from which the CNTs grow directly, thus ensuring a strong physical bond to the carbon fiber.

[0008] The second and final active layer is a thin, dense, and conformal layer of pyrolytic carbon (PyC) that is deposited directly onto the existing CNT structure. This PyC layer fulfills a dual function: it fills the micro-gaps within the CNT structure, fixes the nanotubes, and simultaneously forms a continuous, highly stiff, and structurally homogeneous carbon interface.

[0009] The PyC layer serves as an important buffer for interfacial tensions and as a chemical bridging element. By providing a clean, low-reactivity, and structurally compatible carbon surface, PyC promotes superior chemical affinity and robust adhesion—whether through covalent or strong secondary bonds—with various matrix materials such as epoxy, vinyl ester, or thermoplastic polymers.

[0010] The final component consists of a polymer, ceramic, or metal matrix material that completely encapsulates the hybrid-coated carbon fiber. The combination of the highly robust PyC surface and the underlying CNT structure promotes superior mechanical interlocking and chemical affinity—a significant improvement over the smooth surface of conventionally dimensioned or uncoated fibers.

[0011] The two-layer nanocoating fundamentally alters the stress distribution at the fiber-matrix interface. The CNT / PyC architecture enables more uniform load transfer, thus reducing the stress concentrations typical of conventional interfaces. This results in a composite component with significantly improved mechanical reliability.

[0012] The component system thus exhibits superior mechanical properties, manifested in significantly higher interfacial shear strength and improved resistance to fatigue and microcracking. This structural enhancement directly translates into a longer service life and higher operating limits for composite materials used in highly stressed applications.

Claims

[1] A fiber-reinforced composite component consisting of a carbon fiber and a matrix material, wherein the carbon fiber is provided with a hybrid nanocoating consisting of an inner layer of carbon nanotubes that adhere directly to the fiber surface and an outer layer of pyrolytic carbon that conformally covers the carbon nanotubes. [2] Component according to claim 1, wherein the outer layer of pyrolytic carbon completely encloses the inner layer of carbon nanotubes, thus forming a continuous, highly rigid carbon interface for chemical bonding with the matrix material. [3] Component according to claim 1, wherein the inner layer of carbon nanotubes provides a three-dimensional physical interlocking mechanism and significantly increases the effective surface area of ​​the fiber. [4] Component according to claim 1, characterized bythat the hybrid nanocoating structure significantly increases the interfacial shear strength and improves resistance to microcracks compared to a composite component with carbon fibers without hybrid nanocoating.