Microhardness and heat-resistance performance of ferromagnetic cobalt-molybdenum nanocrystals electrodeposited from an aqueous solution containing citric acid

Abstract

Using a potentiostatic electrodeposition technique, nanocrystalline cobalt-molybdenum (Co-Mo) superalloys containing molybdenum oxide (MoO _X ) were synthesized from an aqueous solution containing citric acid. Molybdenum content in the alloys was controlled up to approximately 53% by adjusting the cathode potential during the alloy electrodeposition. Based on the XRD profiles and electron diffraction patterns, an amorphous-like nanocrystalline structure was observed in the alloys with high molybdenum content. XPS analysis revealed that the chemical state of electrodeposited molybdenum was almost metallic and the oxide state was also detected partially. According to the magnetization curves, the coercivity of electrodeposited Co-Mo alloys decreased down to approximately 72 Oe with increasing the molybdenum content up to around 53%. The microhardness reached 845 kgf mm ^−2 in the electrodeposited Co-53%Mo alloy and greatly exceeded that of pure cobalt (ca. 250–300 kgf mm ^−2 ). Heat resistance performance of the electrodeposited nanocrystalline Co-53%Mo alloy was improved by the Mo alloying effect because the recrystallization and oxidation behavior were not observed even if the annealing temperature was increased up to 700 °C.

Keywords

• electrodeposition
• cobalt
• molybdenum
• nanocrystal
• microhardness
• heat resistance