Per: VINICIUS OLIVEIRA DOS SANTOS (LEBM/HU-UFSC), pATRICIA oRTEGA cUBILLOS (lebm/hu-ufsc), Carlos Rodrigo de Melo Roesler (LEBM/HU-UFSC), Joseph quadri NOVY (LEBM/HU-UFSC)
Abstract:
The microstructure of metallic material influence the mechanical behaviour of the product. However, the standards ISO 5832-4 and ASTM F75, that contain the requirements of Cobalt-Chromium-Molybdenum Alloy Castings for surgical implants, don’t specify the acceptable microstructure. The aim of the current work is evaluating the microstructure influence in the premature failure of a femoral stem manufacturer in cobalt-chromium-molybdenum casting alloy. The stem fractured during the in vitro testing. After this, the stem was sectioned to material characterization and fractography analyze. The material of the stem was accorded with the requirements of ISO 5832-4 and ASTM F75 standard in relation to chemical composition, microstructure and hardness. The fracture occurred by fatigue mechanism, with evidences of micromechanism of fatigue with cleavage in about 50% of the area fractured. Were detected secondary cracks with inclusions close, possible carbides M23C6. The high amount of carbides probably was the cause of failure, due to generate intern stress fields that facilitate the nucleation and propagation of microcracks. The results indicate the need to include, in the associated technical standards, specifications to microstructure of cobalt-chromium-molybdenum casting alloy, aiming to ensure a greater safety of femoral stems.