Effect of Heat Treatment on the Corrosion Resistance in a Co–28Cr–6Mo Alloy Casting for Surgical Implants

摘要

AbstractCorrosion resistance in a Co–28Cr–6Mo alloy casting and its effect before and after a heat treatment (HT) have been studied in this work. The corrosion behavior was evaluated with a potentiodynamic polarization test, and the electrolyte solution employed consisted of a Hank’s solution at 37?°C. The heat treatments were achieved by holding at 1150, 1200 and 1230?°C for 4 and 5?h followed by quenching. Microstructural analyses were carried out by optical and scanning electron microscopy. The as-cast Co–28Cr–6Mo alloy reveals a large amount of blocky carbides at the grain boundaries and at interdendritic zones. A corrosion rate of 0.3608?mpy was obtained, and the observed microstructure is associated with an intergranular corrosion mechanism. After heat treatment, carbides got smaller, being mostly globular. Corrosion rates of 0.2552 and 0.1669?mpy were obtained on heat-treated samples at 1150?°C for 5?h and 1230?°C for 4?h, respectively. The microstructures observed on heat-treated samples are also associated with an intergranular corrosion mechanism. The potentiodynamic polarization tests indicate that for all cases, the corrosion rate decreased applying a heat treatment. The corrosion rate was minimized with a heat treatment at 1230?°C for 4?h.]]>