Evolution of structural, mechanical and tribological properties of Ni-P/MWCNT coatings as a function of annealing temperature

Collaborative research project Hardalt (Grant No. 606110) funded by the EU's seventh framework programme

Ready-to-Use Recycled Carbon Fibres Decorated with Magnetic Nanoparticles: Functionalization after Recycling Process Using Supercritical Fluid Chemistry

An innovative simultaneous process, using supercritical fluid (SCF) chemistry, was used to recycle uncured prepregs and to functionalize the recovered carbon fibres with Fe3O4 magnetic nanoparticles (MNPs), to produce a new type of secondary raw material suitable for composite applications. This specific functionalization allows the fibres to be heated by induction through a hysteresis loss mechanism characteristic for nanoparticle susceptor-embedded systems, for triggered healing properties and a potentially easy route for CF reclamation. Using SCF and hydrothermal conditions for recycling, functionalization of fibres can be performed in the same reactor, resulting in the creation of ready-to-use fibres and limiting the use organic solvent. After cutting the uncured prepreg to the desired length to fit in future applications, supercritical CO2 extraction is performed to partially remove some components of the uncured prepreg matrix (step 1). Then, the recycled carbon fibres (rCFs), still embedded inside the remaining organic matrix, are brought into contact with reactants for the functionalization step (step 2). Two possibilities were studied: the direct synthesis of MNPs coated with PAA in hydrothermal conditions, and the deposition of already synthesized MNPs assisted by supercritical CO2-acetone. No CF surface activation is needed thanks to the presence of functional groups due to the remaining matrix. After functionalization, ready-to-use material with homogeneous depositions of MNPs at the surface of rCF is produced, with a strong magnetic behaviour and without observed degradation of the fibres

3D printed CFRPs and micro-composite products by design from recycled resources

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Inductive Thermal Effect on Thermoplastic Nanocomposites with Magnetic Nanoparticles for Induced-Healing, Bonding and Debonding On-Demand Applications

In this study, the heating capacity of nanocomposite materials enhanced with magnetic nanoparticles was investigated through induction heating. Thermoplastic (TP) matrices of polypropylene (PP), thermoplastic polyurethane (TPU), polyamide (PA12), and polyetherketoneketone (PEKK) were compounded with 2.5–10 wt.% iron oxide-based magnetic nanoparticles (MNPs) using a twin-screw extrusion system. Disk-shape specimens were prepared by 3D printing and injection molding. The heating capacity was examined as a function of exposure time, frequency, and power using a radio frequency (RF) generator with a solenoid inductor coil. All nanocomposite materials presented a temperature increase proportional to the MNPs’ concentration as a function of the exposure time in the magnetic field. The nanocomposites with a higher concentration of MNPs presented a rapid increase in temperature, resulting in polymer matrix melting in most of the trials. The operational parameters of the RF generator, such as the input power and the frequency, significantly affect the heating capacity of the specimens, higher input power, and higher frequencies and promote the rapid increase in temperature for all assessed nanocomposites, enabling induced-healing and bonding/debonding on-demand applications

Effect of annealing temperature on microstructure, mechanical and tribological properties of nano-SiC reinforced Ni-P coatings

The tribological properties of Ni-P/SiC nanocomposite coatings annealed at different temperatures (350–500 °C) were investigated in order to determine the optimal temperature needed to enhance their wear resistance as well as to reveal the underlying wear mechanisms. With increasing annealing temperature, the hardness of the annealed coatings gradually decreased from 8.2±0.5 to 7.1±0.6 GPa as a result of the Hall-Petch effect, nevertheless these values obtained were constantly higher than that of the as-plated coating (6.3±0.3 GPa) due to the formation of a hard Ni3P phase. Regarding to tribological properties, the Ni-P/SiC coating annealed at 350 °C presented a poorer wear resistance (6.1×10-5 mm3/Nm) compared to the as-plated coating (3.9×10-5 mm3/Nm) owing to a rougher original contact surface and the subsequent generation of nickel and iron oxides on the wear track. In contrast, coatings annealed at temperatures ranging between 400–500 °C exhibited the improved wear resistance (4.3×10-5 – 7.8×10-6 mm3/Nm) attributable to their smoother surfaces and to the lubrication effect of H3PO4 arising from the tribochemical reaction between Ni3P and the environment. Overall, the Ni-P/SiC coating annealed at 500 °C containing the largest amount of Ni3P exhibited the lowest friction coefficient (0.51) and wear rate (7.8×10-6 mm3/Nm)

Evolution of structural, mechanical and tribological properties of Ni–P/MWCNT coatings as a function of annealing temperature

The structural, mechanical and tribological properties of Ni–P/MWCNT coatings annealed at various temperatures (350–500 °C) were investigated using XRD, SEM, nanoindentation and tribometer to determine the optimal annealing temperature for their enhanced tribological properties. The results showed that the annealed coatings comprised a hard Ni3P phase, and consequently presented a higher hardness (from 7.0 ± 0.3 to 8.2 ± 1.4 GPa) than the as-plated sample (6.0 ± 0.9 GPa). With the annealing temperature increasing from 350 °C to 500 °C, the crystallinity of coating was enhanced with larger crystal grains of Ni and Ni3P, which led to a decline in hardness (from 8.2 to 7.0 GPa) due to the Hall-Petch effect. Owing to the lubrication effect of H3PO4 arising from the tribochemical reaction of Ni3P with ambient environment, the annealed samples exhibited lower friction coefficients (0.71 ~ 0.86) compared to the as-plated coating (0.87). A combination of low surface roughness and the reduction of oxides on wear track contributed to the lowest friction coefficient of Ni–P/MWCNT annealed at 400 °C. However, the decomposition of amorphous carbon in MWCNT over 380 °C produced less dense coatings (for annealing temperatures 400–500 °C), and their incompact structure led to a higher wear rate (2.9–3.0 × 10? 5 mm3/Nm) compared to the as-plated sample (2.4 × 10? 5 mm3/Nm). In contrast, Ni–P/MWCNT coating annealed at 350 °C (< 380 °C) exhibited a better wear resistance (4.3 × 10? 6 mm3/Nm). Thus, 350 °C was found to be the optimal annealing temperature to lower the friction coefficient and enhance the wear resistance of Ni–P/MWCNT coating