Influence of crystallisation an amorphous Co77Si11.5B11.5 alloy on corrosion behavior

Purpose: This paper describes crystallization kinetics and its influence on changes of electrochemical behavior of amorphous, amorphous relaxed and nanocrystalline Co77Si11,5B11,5 alloy. Design/methodology/approach: The following experimental techniques were used: structural research - X-ray diffraction (XRD) and electrochemical investigations were carried out by means of an electrochemical impedance spectroscopy method. Findings: Heat treatment of amorphous Co77Si11,5B11,5 alloy leads to the formation of the hexagonal alpha-Co phase in an amorphous matrix at the temperature T = 798 K and this is the first stage of the crystallization process. At the temperature T = 873 K appearance of boride phase Co2B, Co3B and silicates phase Co2Si was state. It is the second stage of crystallization. The existence of boride phases was confirmed by after annealing in the temperature range from 730 K up to 873 K. The secondary crystallization is known to cause grain coarsening of phases and the electrochemical properties. The analysis leads to the conclusion that in view of data obtained from electrochemical tests in 3% NaCl solution, the crystallization process begins at lower temperatures than resulting from XRD data Co77Si11,5B11,5 alloy. Practical implications: The attractive properties of Co-Si-B alloy are of special interest for basic research on the materials as well as for their potential applications. Due to their numerous potential application nanocrystalline cobalt based alloys could be work in a wet industrial and marine atmosphere containing sulphide and chloride ions. Electrochemical corrosion can changes structure and magnetic properties of Co-based alloys. Originality/value: It has been shown that thermal annealing at temperature lower than the crystallization temperature leads to a significant changes of the initial electrochemical behaviour in 3% NaCl solution.