L. D. Zardiackas, S. Williamson, M. Roach, University of Mississippi Medical Center, Jackson, MS; V. R. Jablokov, H. Freese, ATI Allvac, Monroe, NC
The presence or absence of stress corrosion cracking (SCC) in the failure of titanium implants has been the subject of conjecture and controversy. Research in our laboratories has shown no SCC effects on the fracture surfaces of several titanium alloys tested in distilled/de-ionized water and in Ringer’s solution at physiological body temperature. The purpose of this study was to evaluate the SCC properties of α/β Ti-15Mo and compare them to Ti-6Al-4V ELI (α + β) and β Ti-15Mo. Smooth SCC samples were machined using low stress grind procedures to a gauge length of 10 mm and a gauge diameter of 4 mm. Notched SCC samples were machined with a root notch diameter of 4 mm and a notch width of 1 mm to obtain a Kt of 3.2. Triplicate smooth and notched samples were tested in distilled/de-ionized water (DI) and Ringer’s solution at 37ºC using an MTS servo hydraulic test system. Testing was performed using the slow strain rate method outlined in ASTM G129. Measurements of the fractured samples allowed for calculations of percentage of elongation (PE) and reduction of area (ROA). The percentage of elongation ratio (PER) and reduction of area ratio (ROAR) were calculated by dividing the mean values in Ringer’s solution by the mean values in DI water. SEM was used to examine the fractured surfaces. PER and ROAR ratios less than 0.90 indicate that SCC mechanisms may be present, while ratios closer to 1.00 indicates less susceptibility. The PER and ROAR ratios for all alloys tested were near or greater than 1.00, therefore, SCC mechanisms were not expected. SEM analysis of the fractured surfaces of smooth and notched SCC samples revealed a cup and cone type of fracture with equiaxed ductile dimples and no evidence of SCC mechanisms was observed regardless of test solution.
Summary: The purpose of this study was to evaluate the SCC properties of
a/
b Ti-15Mo and compare them to Ti-6Al-4V ELI (
a +
b) and
b Ti-15Mo. Triplicate smooth and notched samples were tested in distilled/de-ionized water (DI) and Ringer’s solution at 37°C. Testing was performed using the slow strain rate method outlined in ASTM G129. The PER and ROAR ratios for all alloys tested were near or greater than 1.00, therefore, SCC mechanisms were not expected. SEM analysis of the fractured surfaces of smooth and notched SCC samples revealed a cup and cone type of fracture with equiaxed ductile dimples and no evidence of SCC mechanisms was observed regardless of test solution.
