Evaluate the use of Elgiloy (Co-Cr-Ni alloy) for wave springs in implantable medical devices.

Elgiloy is a cobalt-chromium-nickel-molybdenum alloy that is highly valued for medical implants due to its extreme biocompatibility, high fatigue strength, and excellent corrosion resistance in body fluids. For a wave spring in a prosthetic joint or heart valve, Elgiloy provides a higher 'Elastic Energy Storage' capacity than 316L stainless steel. Its processing involves a combination of cold work and aging (typically 480 C for 5 hours), resulting in a tensile strength exceeding 1900 MPa. Its modulus $E$ remains stable at 200 GPa. Furthermore, it is non-magnetic, which is crucial for patients requiring MRI scans. The primary design challenge is its high cost and the difficulty in coiling the material due to its high work-hardening rate.