Electrochemical study of aluminum–cubic boron nitride composites synthesized via spark plasma sintering for engineering applications

Herein, aluminum−cubic boron nitride (Al−BN) composites with different reinforcement sizes (20, 40, and 60 µm) were developed via spark plasma sintering while maintaining a constant weight percentage (10 wt%; reinforcement). The powder materials were sintered at a temperature of 550 °C and constant uniaxial pressure of 50 MPa with a heating rate of 100 °C/min. Field-emission scanning electron microscopy analysis of the developed composites revealed a uniform dispersion in the Al matrix. X-ray diffraction analysis indicated the presence of aluminum and cubic boron nitride major and minor phases, respectively. Evidence of chemical reactions and the presence of an interfacial phase were not observed at 550 °C in the Al−cBN composite. The mechanical and electrochemical properties of the composites were investigated as a function of the cBN particle size. The results demonstrated that the composite with a cBN particle size of 20 µm (i.e., more particles in the Al matrix than other compositions) strengthens the matrix owing to the better stress drive in the matrix and exhibits the highest average hardness (1.78 GPa), elastic modulus (76.1 GPa), and percentage of densification (98.1%) compared to the other tested composites. The corrosion behavior and resistance against pitting corrosion of pure Al and cBN-based composites were investigated in a 3.5 wt% NaCl solution using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization analyses. Electrochemical studies revealed that among the analyzed samples, the composite with 20 µm cBN particles exhibits an excellent polarization resistance, in addition to the lowest corrosion rate (∼5 mills per year) and a very high resistance to pit formation in a corrosive environment.