EFFECT OF COLD WORK AND AGING ON A COBALT-NICKEL BASED ALLOY

摘要

Cobalt-nickel based MP35N (35Co, 35Ni, 20Cr, lOMo) alloy is characterized by a combination of extremely high strength, high toughness, corrosion resistance and ductility. In this study, experiments were carried out to investigate the influence of cold work and aging treatment on its mechanical properties. An annealed material was cold worked to 30-90% reduction and aged at temperatures from 400 to 700°C for 10 minutes to 16 hours. It is found that this material work hardened rapidly with strength almost doubled after 30% cold work. Aging provides a secondary strengthening, which depends on the aging temperature and previous cold work level. An excellent combination of mechanical properties can be obtained from the material with 75%cw and aged at ~500°C for 2-4 hours, where the Yield Strength (Y.S) larger than 2000MPa, the Ultimate Tensile Strength (UTS) above 2200MPa and the Reduction of Area (RA) -40% can be achieved. TEM observations and synchrotron X-ray diffractions suggest the work hardening is caused by the increased density of dislocations, the development of the <111>and <100>texture and the deformation twins, while the secondary age hardening is associated with the increased number of micro-twins produced during the aging process.