Corrosion Behavior of Experimental Cast Ti-Au Alloys

Objective: This study examined the electrochemical behavior of a series of binary Ti-Au alloys. Methods: Alloys (5, 10, 20, 30, and 40 mass% Au) were prepared in an argon-arc melting furnace. Each alloy was cast into a magnesia mold (Selevest CB, Selec, Japan) using a two-compartment/pressure casting unit (Castmatic-S, Iwatani, Japan). The hardened surface layer (300 µm) was removed from the cast surfaces prior to the corrosion test, producing specimens measuring 8 mm x 8 mm x 2 mm. Anodic polarization information (n = 4) for the alloys was obtained in a deaerated 0.9% NaCl solution at 37°C. Alloy structures and phases were examined with an optical microscope, SEM/EDS, and XRD. XRD revealed the existence of Ti₃Au in the alloy with Au ³ 30%. Data from the anodic polarization, primary passivation potential (Epp), passive current densities (ipassive), and breakdown potential (Eb) were pooled and analyzed by a non-parametric method (a = 0.05) and compared with data for CP Ti (control). Results: The Epp of all alloys was near -0.1(V vs. SCE), whereas the ipassive ranged form 1.5 to 2.0 (µA/cm²). There were no significant differences in these parameters (p ³ 0.20). The Eb (V vs. SCE) of the alloys with Au ³ 20% was significantly different (p £ 0.03) from that of CP Ti.

Metal	5%Au	10%Au	20%Au	30%Au	40%Au	CP
Mean	2.12a	2.06a	1.81b	1.22b	0.63c	2.24a
SD	0.07	0.06	0.10	0.62	0.02	0.25

Identical letters indicate no statistical differences (p > 0.05).

The microstructures of the corroded surfaces of the alloys with Au ³ 20% showed the deterioration of precipitated Ti₃Au along the grain boundaries of the equiaxed alpha titanium grains. Conclusion: The reduced Eb of the high Au alloys was the result of the preferential dissolution of Ti₃Au in the structure. Partially supported by NIH/NIDCR grant DE11787.