Nanocrystalline structure and microhardness of cobalt-chromium alloys electrochemically synthesized using a metal hydroxide coprecipitation technique

Abstract

The effect of glycine as a complexing agent on metal hydroxide formation, such as Co(OH) _2 and Cr(OH) _3 , was investigated based on potential-pH diagrams and titration curves for Co ^2+ -H _2 O and Cr ^3+ −H _2 O systems. Using a potentiostatic electrodeposition technique, Co–Cr alloy-based composite films containing Cr _2 O _3 were synthesized from a non-suspended aqueous solution within an optimized pH range. Chromium content in the composite films was controlled up to 38.9% 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 composite films with high chromium content. The average crystal grain size declined due to Cr _2 O _3 particles and hydrogen evolution during the electrodeposition process. Saturation magnetization of the composite films decreased with an increase in the chromium content. Synergistic contribution of increasing dislocation density and refining crystal grain size improved the microhardness of the composite films. The microhardness reached 624.2 kgf mm ^−2 and greatly exceeded that of pure cobalt (ca. 250–300 kgf mm ^−2 ).

Keywords

• coprecipitation
• electrodeposition
• cobalt
• chromium
• nanocrystal
• microhardness