Synergistic Reinforcement of Cu/Ti₃SiC₂/C Nanocomposites with Graphene and MWCNTs: Microstructure and Mechanical Performance

Abstract

Combining one‑dimensional multi‑walled carbon nanotubes (MWCNTs) with two‑dimensional graphene creates a synergistic interface that enhances the dispersion, wettability, and bonding of reinforcement particles in a copper matrix. Using mechanical alloying, vacuum hot‑pressing (VHP), and hot isostatic pressing (HIP), we fabricated Cu/Ti₃SiC₂/C nanocomposites with varying ratios of graphene and MWCNTs. X‑ray diffraction, optical microscopy, SEM, TEM, and EPMA revealed a fine, well‑bonded microstructure. Mechanical testing showed that the optimal composition—0.8 wt % MWCNTs and 0.2 wt % graphene—delivers the highest hardness and tensile strength, owing to grain refinement, load transfer, Orowan strengthening, and interfacial adhesion. These findings confirm that a dual‑phase carbon reinforcement strategy can markedly improve the performance of Cu‑based composites.

Background

Copper–graphite composites combine copper’s excellent conductivity with graphite’s self‑lubricating properties, making them attractive for aerospace, electronics, and automotive applications. Ti₃SiC₂ adds high‑temperature stability, oxidation resistance, and thermal conductivity. However, Cu/Ti₃SiC₂/C composites alone still lag in strength and wear resistance. Introducing nanoscale reinforcements—MWCNTs and graphene—can improve these properties, but challenges such as poor dispersion, limited wettability, and weak interfaces have hindered progress. Recent studies suggest that a hybrid of MWCNTs and graphene can form a high‑contact‑area network, improving load transfer and interfacial bonding.

Methods/Experimental

Raw powders of Cu, Ti₃SiC₂, graphite, MWCNTs, and graphene nanoplatelets were first dispersed by ultrasonic agitation. Surface modifications were performed using Ar–NH₃ plasma and low‑concentration Rutin or Gallic acid solutions to enhance wettability. High‑energy ball milling (Agate media) mixed the powders at a 10:1 mass ratio with tert‑butyl alcohol as a binder. The resulting mixture was dried and then sintered via VHP (950 °C, 20 MPa, 2 h) followed by HIP (900 °C, 100 MPa, 2 h). Relative densities were measured by Archimedes' principle. Microstructure was examined by OM, XRD, SEM/EDS, and TEM. Hardness, compression, and shear tests were conducted on a universal testing machine at 0.5 mm/min. All data were compared across compositions of 0.8 wt % graphene/0.2 wt % MWCNT, 0.5/0.5, and 0.2/0.8.

Results and Discussion

Powder Microstructure and Phase Identification

SEM images confirmed that MWCNTs bridged Cu particles while graphene layers dispersed within the matrix, reducing agglomeration. XRD patterns showed retention of Cu, Ti₃SiC₂, and graphite phases, with no evidence of oxidation or unwanted reactions. Mechanical alloying preserved phase integrity while promoting intimate contact between reinforcements and the copper matrix.

Composite Microstructure

Metallography revealed a continuous Cu matrix interspersed with Ti₃SiC₂ grains and isolated graphite or carbon clusters. Ti₃SiC₂ decomposed at 950 °C to TiC and Si, the latter forming Cu₉Si solid solutions that enhance interfacial bonding. EPMA mapping confirmed uniform distribution of Cu, Ti, Si, C, and La (added for densification).

Phase Transformations During Sintering

Thermodynamic analysis confirmed that Ti₃SiC₂ → 3TiC₂/₃ + Si (ΔG = ‑106.5 kJ mol⁻¹) is spontaneous. Subsequent reactions (Si + 9Cu → Cu₉Si) and (C + Si → SiC) were also exothermic, leading to the observed TiC and Cu₉Si phases in the final microstructure.

Mechanical Properties

Hardness decreased by only ~9 % when increasing graphene from 0.5 wt % to 0.8 wt %, indicating that excessive graphene promotes agglomeration and porosity. Tensile and compressive strengths declined by ~12 % at 0.8 wt % graphene, while shear strength reduced by ~20 %—all consistent with weaker interfacial bonding and increased micro‑crack formation. The optimal 0.8 wt % MWCNT/0.2 wt % graphene composition exhibited the highest densification (≈97 % theoretical) and mechanical performance.

Tensile Fracture Analysis

SEM of fracture surfaces showed typical dimples and cleavage facets, with evidence of graphene pull‑out and MWCNT fragmentation. Agglomerated graphene sheets contributed to micro‑crack initiation, whereas well‑distributed MWCNTs improved load transfer. The balance of these effects determines the overall toughness.

Conclusions

1. Vacuum hot‑pressing and HIP effectively produce Cu/Ti₃SiC₂/C composites reinforced with MWCNTs and graphene.
2. Synergy arises from high compactness, homogeneous dispersion, and strong interfacial bonding.
3. The best mechanical performance is achieved with 0.8 wt % MWCNTs and 0.2 wt % graphene; beyond this, agglomeration degrades properties.
4. Enhancements stem from grain refinement, load‑transfer, Orowan, and interfacial strengthening.