High-Temperature Oxidation and Corrosion Behavior of Al–Co Alloys Prepared by the Combustion Synthesis Process
摘要
Combustion synthesis is a novel method for rapid, low-cost production of various types of materials such as intermetallic compounds, ceramic materials, and composites. In this paper, the Al–Co alloy was produced via the combustion synthesis technique. Powder mixtures of cobalt and aluminum powders with a 1:1 atomic ratio were pressed to prepare green specimens, which were then ignited by rapid heating, resulting in a highly exothermic reaction between the reactants and formation of cobalt aluminides as the reaction product. Various amounts of boron were added to the initial mixture to investigate the effect of boron on the oxidation and corrosion properties of the alloy. The microstructural evolution and phase changes after exposing the samples to an oxidizing atmosphere at 900 °C to 1100 °C for different were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. Moreover, the effect of boron on the corrosion behavior of samples was studied using potentiodynamic polarization tests and electrochemical impedance spectroscopy. The results showed that by increasing the percentage of boron up to 0.4 pct, the resistance to oxidation increased. With a further increase in the percentage of boron, the resistance to oxidation tends to decrease, which indicates there is an optimal amount for the use of boron in the samples. Furthermore, by analyzing the corrosion of the samples in 3.5 pct NaCl solution, the samples containing boron showed a higher resistance against the aggressive Cl− ions due to the formation of a denser passive layer. The highest corrosion rates were found in the boron-free alloy.