Abstract
The stress-corrosion cracking (SCC) behavior of two surgical implant materials, 316L stainless steel and Ti-6Al-4V ELI, has been examined in various Cl containing environments. Tests have been conducted using fracture mechanics type samples in boiling 44% MgCl2 (154 °C) and two solutions at 37°C -5% HCl and a physiological saline solution. Data has been acquired with respect to incubation time, crack propagation velocity, and threshold stress intensity. Cracking has been observed in all environments tested. The results generally indicate that the titanium alloy examined is more resistant to crack initiation than is 316L, but that a crack, once formed, propagates more readily in Ti-6Al-4V ELI. For 316L, experiments were conducted regarding the influence of applied polarization on the stress-corrosion crack initiation and growth kinetics. Effects can be observed for all of the parameters mentioned above, but the most important result for implant alloys appears to be a lowering of incubation time with applied polarization. In a separate study of the potentiodynamic polarization behavior of stressed alloys, alterations in the passive layer were still evident one week after stress application. The importance of these findings for the surgical implant field and comparisons with other studies of implant SCC are discussed.
