Official Answer
Answer
Medical implants (e.g., prosthetic joints) require materials that are both biocompatible and exhibit high fatigue strength in corrosive body fluids. Elgiloy (a Co-Cr-Ni-Mo alloy) and MP35N offer exceptional corrosion resistance and high modulus. They are often processed to a high tensile strength ($>250 ksi$) through cold work and aging. Unlike 300-series stainless, they are non-magnetic, which is crucial for MRI compatibility. The design must account for the higher density $\rho \approx 8.4 g/cm^3$ and the slightly higher $E$ ($235 GPa$ vs $190 GPa$ for 17-7PH) when calculating spring rates for precision surgical instruments.
