A team of researchers recently published a paper available as a pre-proof in the journal Ceramics International that evaluated the electrical conductivity and mechanical strength of copper-nickel/alumina (Cu-Ni/Al2O3) nanocomposites manufactured using the in situ chemical reaction technique.
Study: Development and performance analysis of novel in situ Cu–Ni/Al2O3 nanocomposites. Image Credit: luchschenF/Shutterstock.com
Cu-Ni alloys are increasingly gaining prominence in different industrial applications owing to their excellent mechanical and physical properties such as corrosion resistance, thermal and electrical conductivity, and tolerance to high heat and stress.
Although several alloying elements such as Ni, zinc (Zn), and aluminum (Al) are commonly used in copper-based alloys, Ni is more suitable compared to the others in terms of solids and liquid temperature.
The characteristics of the Cu-Ni matrix can be improved further by reinforcing the matrix with Al2O3 as nano-scale Al2O3 particles can successfully prevent Cu matrix recrystallization and obstruct the grain boundary movement.
In this study, researchers investigated the effect of the Al2O3 nanoparticles on the thermal and electrical conductivities, thermal expansion, and structure of the synthesized Cu-Ni/Al2O3 nanocomposites.
Water-soluble powders of aluminum nitrate (Al (NO3)3.9H2O), nickel nitrate (Ni (NO3)2.6H2O), and copper nitrate (Cu (NO3)2.3H2O) were mixed in water, and then the mixture was heated for 30 min at 70°C.
Nitrate salt powder precursor particles were obtained using a sprayer on the mixture at 180°C, and those particles were then oxidized for 60 min at 850°C to obtain the Al2O3, nickel oxide (NiO), and copper oxide (CuO) nanocomposite powders.
Subsequently, Ni and Cu nanocomposite powders were prepared by the reduction of CuO and NiO powders for 30 min at 30°C in hydrogen flux, followed by cooling under a high-purity argon atmosphere. 8, 5, and 3 wt.% Al2O3 were added to the Cu-Ni/Al2O3 nanocomposites in order to evaluate the impact of Al2O3 on the nanocomposites at these concentrations.
A hydraulic press at 700 MPa was used to compress the Cu-Ni/Al2O3 nanocomposite powders within a steel mold to create cylindrical-shaped samples.
Subsequently, the samples were sintered for 2 hours at 900°C in a hydrogen environment within a ceramic tubular furnace, with cooling and heating rates of 2 and 5°C/min, respectively.
The nanocomposite powders were analyzed after deoxidization using X-ray diffraction (XRD) at 26 mA and 36 kV, and the X-ray data were obtained with the scanning scope of 20–80° in steps of 0.02° (2θ).
Transmission electron microscopy (TEM) was used to investigate the Al2O3 created from the Cu-Ni/Al2O3 nanocomposite powders, while field emissions scanning electron microscope (FESEM) with energy-dispersive X-ray spectroscopy (EDS) was employed to analyze the microstructure of the synthesized nanocomposites.
The electrical resistivity of the nanocomposites after sintering was determined by a four-probe approach using the Omega CL 8400-micrometer equipment, while the electrical conductivity was measured using a four-terminal ohmmeter.
A Netzsch dilatometer type 402 C pushrod was utilized to measure the coefficient of thermal expansion (CTE) of the nanocomposites after the samples were heated in the open air at a rate of 3 K/min between 25 and 500°C.
The morphology of the synthesized powders after deoxidization with different concentrations of Al2O3 revealed huge particle groups, and the average size of the particles was less than 20 nm.
No morphological changes were observed between the three nanocomposites, and their particle sizes remained identical.
The size of Al2O3 nanoparticles was 20 nm with a spherical shape, and the nanoparticles were uniformly dispersed throughout the Cu-Ni matrix at a scale of 1 µm.
The findings indicated the effectiveness of the in situ method for synthesizing reinforced metal matrix nanocomposites.
XRD analysis demonstrated the effective dissolution of Ni and Cu, indicating the accuracy of the in situ reaction.
No agglomeration was observed in the microstructure of the nanocomposites, indicating that the mechanical properties of nanocomposites primarily rely on their structural homogeneity. A lack of impurities was observed in the EDS of Cu-Ni/8%Al2O3.
The porosity percentage and microhardness of the Cu-Ni/Al2O3 nanocomposites increased with the increasing concentration of Al2O3, while the density decreased.
The porosity percentage increased from 3.7% in the Cu-Ni matrix to 10.8% in the Cu-Ni-8%Al2O3 nanocomposite. Similarly, the microhardness increased from 53.3 HV in the Cu-Ni matrix to 92.7 HV in the Cu-Ni-8%Al2O3 nanocomposites.
The hardness improved due to several strengthening mechanisms triggered by Al2O3 nanoparticles.
The resistivity of the nanocomposites increased and conductivity decreased with the increasing concentration of Al2O3 in the nanocomposites.
The electrical conductivity decreased from 77.45 International Annealed Copper Standard (IACS) in the pure Cu-Ni matrix to 21.04 IACS in the Cu-Ni/8%Al2O3. Similarly, the thermal conductivity also decreased with rising Al2O3 concentration in the nanocomposites.
The CTE of the synthesized Cu-Ni/Al2O3 nanocomposites was lower than the pure Cu-Ni alloy as the CTE of the Al2O3 nanoparticles is lower than the CTE of the Cu.
Taken together, the findings of this study demonstrated that the addition of Al2O3 nanoparticles can significantly improve the mechanical properties of Cu-Ni/Al2O3 nanocomposites while maintaining relatively good thermal and electrical properties.
M. Elmahdy., M. Ali., A.M. Sadoun. et al. (2022) Development and performance analysis of novel in situ Cu–Ni/Al2O3 nanocomposites. Ceramics International. Available at: https://www.sciencedirect.com/science/article/pii/S0272884222003042