Effect of chromium and molybdenum increment on the crystal structure, nanoindentation and corrosion properties of cobalt based alloys

This study investigates the influence of chromium and molybdenum content (Cr: 20-35 wt%; Mo: 5 and 10 wt%) in a cobalt-chromium-molybdenum alloy system on the phases present in the microstructure, the nanomechanical, and electrochemical behavior of the alloys. A linear increase in the hardness is found in relation to the increasing chromium content for both 5 and 10 wt% Mo contents, whereas reduced modulus demonstrates an inflection at 30 wt% Cr, which is influenced by the molybdenum content. The open-circuit potential, polarization resistivity, and linear sweep voltammetry disclose that passivity of Co-Cr-Mo alloys improves in line with increasing Cr until 30 wt%, with any further increase causing a depreciation in the corrosion properties. X-Ray diffraction and optical metallographic analysis confirm that as the chromium content transitions through the 25-30 wt% range, the sigma (sigma) phase begins to develop within the combined matrix of hexagonal close pack martensite (epsilon) and face-centered cubic austenite (gamma) phase.